Configuration Manual

version 3.0-dev4-2

2024/02/23

This document covers the configuration language as implemented in the version
specified above. It does not provide any hints, examples, or advice. For such
documentation, please refer to the Reference Manual or the Architecture Manual.
The summary below is meant to help you find sections by name and navigate
through the document.

Note to documentation contributors :
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    please update the summary below for easier searching.
1. Quick reminder about HTTP
1.1.
1.2.
1.3.
1.3.1.
1.3.2.
1.4.
1.4.1.
1.4.2.

2.

Configuring HAProxy
2.1.
2.2.
2.3.
2.4.
2.5.
2.6.
2.7.
2.8.

3.

Global parameters
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
3.7.
3.8.
3.9.
3.10.
3.11.

4.

Proxies
4.1.
4.2.
4.3.
4.4.

5.

Bind and server options
5.1.
5.2.
5.3.
5.3.1.
5.3.2.

6.

Cache
6.1.
6.2.
6.2.1.
6.2.2.

7.

Using ACLs and fetching samples
7.1.
7.1.1.
7.1.2.
7.1.3.
7.1.4.
7.1.5.
7.1.6.
7.2.
7.3.
7.3.1.
7.3.2.
7.3.3.
7.3.4.
7.3.5.
7.3.6.
7.3.7.
7.4.

8.

Logging
8.1.
8.2.
8.2.1.
8.2.2.
8.2.3.
8.2.4.
8.2.5.
8.2.6.
8.3.
8.3.1.
8.3.2.
8.3.3.
8.3.4.
8.4.
8.5.
8.6.
8.7.
8.8.
8.9.

9.

Supported filters
9.1.
9.2.
9.3.
9.4.
9.5.
9.6.
9.7.

10.

FastCGI applications
10.1.
10.1.1.
10.1.2.
10.1.3.
10.2.
10.3.

11.

Address formats
11.1.
11.2.
11.3.
When HAProxy is running in HTTP mode, both the request and the response are
fully analyzed and indexed, thus it becomes possible to build matching criteria
on almost anything found in the contents.

However, it is important to understand how HTTP requests and responses are
formed, and how HAProxy decomposes them. It will then become easier to write
correct rules and to debug existing configurations.

First, HTTP is standardized by a series of RFC that HAProxy follows as closely
as possible:
  - RFC 9110: HTTP Semantics (explains the meaning of protocol elements)
  - RFC 9111: HTTP Caching (explains the rules to follow for an HTTP cache)
  - RFC 9112: HTTP/1.1 (representation, interoperability rules, security)
  - RFC 9113: HTTP/2   (representation, interoperability rules, security)
  - RFC 9114: HTTP/3   (representation, interoperability rules, security)

In addition to these, RFC 8999 to 9002 specify the QUIC transport layer used by
the HTTP/3 protocol.

1.1. The HTTP transaction model

The HTTP protocol is transaction-driven. This means that each request will lead
to one and only one response. Originally, with version 1.0 of the protocol,
there was a single request per connection: a TCP connection is established from
the client to the server, a request is sent by the client over the connection,
the server responds, and the connection is closed. A new request then involves
a new connection :

  [CON1] [REQ1] ... [RESP1] [CLO1] [CON2] [REQ2] ... [RESP2] [CLO2] ...

In this mode, often called the "HTTP close" mode, there are as many connection
establishments as there are HTTP transactions. Since the connection is closed
by the server after the response, the client does not need to know the content
length, it considers that the response is complete when the connection closes.
This also means that if some responses are truncated due to network errors, the
client could mistakenly think a response was complete, and this used to cause
truncated images to be rendered on screen sometimes.

Due to the transactional nature of the protocol, it was possible to improve it
to avoid closing a connection between two subsequent transactions. In this mode
however, it is mandatory that the server indicates the content length for each
response so that the client does not wait indefinitely. For this, a special
header is used: "Content-length". This mode is called the "keep-alive" mode,
and arrived with HTTP/1.1 (some HTTP/1.0 agents support it), and connections
that are reused between requests are called "persistent connections":

  [CON] [REQ1] ... [RESP1] [REQ2] ... [RESP2] [CLO] ...

Its advantages are a reduced latency between transactions, less processing
power required on the server side, and the ability to detect a truncated
response. It is generally faster than the close mode, but not always because
some clients often limit their concurrent connections to a smaller value, and
this compensates less for poor network connectivity. Also, some servers have to
keep the connection alive for a long time waiting for a possible new request
and may experience a high memory usage due to the high number of connections,
and closing too fast may break some requests that arrived at the moment the
connection was closed.

In this mode, the response size needs to be known upfront so that's not always
possible with dynamically generated or compressed contents. For this reason
another mode was implemented, the "chunked mode", where instead of announcing
the size of the whole size at once, the sender only advertises the size of the
next "chunk" of response it already has in a buffer, and can terminate at any
moment with a zero-sized chunk. In this mode, the Content-Length header is not
used.

Another improvement in the communications is the pipelining mode. It still uses
keep-alive, but the client does not wait for the first response to send the
second request. This is useful for fetching large number of images composing a
page :

  [CON] [REQ1] [REQ2] ... [RESP1] [RESP2] [CLO] ...

This can obviously have a tremendous benefit on performance because the network
latency is eliminated between subsequent requests. Many HTTP agents do not
correctly support pipelining since there is no way to associate a response with
the corresponding request in HTTP. For this reason, it is mandatory for the
server to reply in the exact same order as the requests were received. In
practice, after several attempts by various clients to deploy it, it has been
totally abandoned for its lack of reliability on certain servers. But it is
mandatory for servers to support it.

The next improvement is the multiplexed mode, as implemented in HTTP/2 and
HTTP/3. In this mode, multiple transactions (i.e. request-response pairs) are
transmitted in parallel over a single connection, and they all progress at
their own speed, independent from each other. With multiplexed protocols, a new
notion of "stream" was introduced, to represent these parallel communications
happening over the same connection. Each stream is generally assigned a unique
identifier for a given connection, that is used by both endpoints to know where
to deliver the data. It is fairly common for clients to start many (up to 100,
sometimes more) streams in parallel over a same connection, and let the server
sort them out and respond in any order depending on what response is available.
The main benefit of the multiplexed mode is that it significantly reduces the
number of round trips, and speeds up page loading time over high latency
networks. It is sometimes visible on sites using many images, where all images
appear to load in parallel.

These protocols have also improved their efficiency by adopting some mechanisms
to compress header fields in order to reduce the number of bytes on the wire,
so that without the appropriate tools, they are not realistically manipulable
by hand nor readable to the naked eye like HTTP/1 was. For this reason, various
examples of HTTP messages continue to be represented in literature (including
this document) using the HTTP/1 syntax even for newer versions of the protocol.

HTTP/2 suffers from some design limitations, such as packet losses affecting
all streams at once, and if a client takes too much time to retrieve an object
(e.g. needs to store it on disk), it may slow down its retrieval and make it
impossible during this time to access the data that is pending behind it. This
is called "head of line blocking" or "HoL blocking" or sometimes just "HoL".

HTTP/3 is implemented over QUIC, itself implemented over UDP. QUIC solves the
head of line blocking at the transport level by means of independently handled
streams. Indeed, when experiencing loss, an impacted stream does not affect the
other streams, and all of them can be accessed in parallel.

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and the
start of a new request. When it receives HTTP/2 connections from a client, it
processes all the requests in parallel and leaves the connection idling,
waiting for new requests, just as if it was a keep-alive HTTP connection.

HAProxy essentially supports 3 connection modes :
  - keep alive    : all requests and responses are processed, and the client
                    facing and server facing connections are kept alive for new
                    requests. This is the default and suits the modern web and
                    modern protocols (HTTP/2 and HTTP/3).

  - server close  : the server-facing connection is closed after the response.

  - close         : the connection is actively closed after end of response on
                    both sides.

In addition to this, by default, the server-facing connection is reusable by
any request from any client, as mandated by the HTTP protocol specification, so
any information pertaining to a specific client has to be passed along with
each request if needed (e.g. client's source address etc). When HTTP/2 is used
with a server, by default HAProxy will dedicate this connection to the same
client to avoid the risk of head of line blocking between clients.

1.2. Terminology

Inside HAProxy, the terminology has evolved a bit over the ages to follow the
evolutions of the HTTP protocol and its usages. While originally there was no
significant difference between a connection, a session, a stream or a
transaction, these ones clarified over time to match closely what exists in the
modern versions of the HTTP protocol, though some terms remain visible in the
configuration or the command line interface for the purpose of historical
compatibility.

Here are some definitions that apply to the current version of HAProxy:

  - connection: a connection is a single, bidiractional communication channel
    between a remote agent (client or server) and haproxy, at the lowest level
    possible. Usually it corresponds to a TCP socket established between a pair
    of IP and ports. On the client-facing side, connections are the very first
    entities that are instantiated when a client connects to haproxy, and rules
    applying at the connection level are the earliest ones that apply.

  - session: a session adds some context information associated with a
    connection. This includes and information specific to the transport layer
    (e.g. TLS keys etc), or variables. This term has long been used inside
    HAProxy to denote end-to-end HTTP/1.0 communications between two ends, and
    as such it remains visible in the name of certain CLI commands or
    statistics, despite representing streams nowadays, but the help messages
    and descriptions try to make this unambiguous. It is still valid when it
    comes to network-level terminology (e.g. TCP sessions inside the operating
    systems, or TCP sessions across a firewall), or for non-HTTP user-level
    applications (e.g. a telnet session or an SSH session). It must not be
    confused with "application sessions" that are used to store a full user
    context in a cookie and require to be sent to the same server.

  - stream: a stream exactly corresponds to an end-to-end bidirectional
    communication at the application level, where analysis and transformations
    may be applied. In HTTP, it contains a single request and its associated
    response, and is instantiated by the arrival of the request and is finished
    with the end of delivery of the response. In this context there is a 1:1
    relation between such a stream and the stream of a multiplexed protocol. In
    TCP communications there is a single stream per connection.

  - transaction: a transaction is only a pair of a request and the associated
    response. The term was used in conjunction with sessions before the streams
    but nowadays there is a 1:1 relation between a transaction and a stream. It
    is essentially visible in the variables' scope "txn" which is valid during
    the whole transaction, hence the stream.

  - request: it designates the traffic flowing from the client to the server.
    It is mainly used for HTTP to indicate where operations are performed. This
    term also exists for TCP operations to indicate where data are processed.
    Requests often appear in counters as a unit of traffic or activity. They do
    not always imply a response (e.g. due to errors), but since there is no
    spontaneous responses without requests, requests remain a relevant metric
    of the overall activity. In TCP there are as many requests as connections.

  - response: this designates the traffic flowing from the server to the
    client, or sometimes from HAProxy to the client, when HAProxy produces the
    response itself (e.g. an HTTP redirect).

  - service: this generally indicates some internal processing in HAProxy that
    does not require a server, such as the stats page, the cache, or some Lua
    code to implement a small application. A service usually reads a request,
    performs some operations and produces a response.

1.3. HTTP request

First, let's consider this HTTP request :

  Line     Contents
  number
     1     GET /serv/login.php?lang=en&profile=2 HTTP/1.1
     2     Host: www.mydomain.com
     3     User-agent: my small browser
     4     Accept: image/jpeg, image/gif
     5     Accept: image/png

1.3.1. The Request line

Line 1 is the "request line". It is always composed of 3 fields :

  - a METHOD      : GET
  - a URI         : /serv/login.php?lang=en&profile=2
  - a version tag : HTTP/1.1

All of them are delimited by what the standard calls LWS (linear white spaces),
which are commonly spaces, but can also be tabs or line feeds/carriage returns
followed by spaces/tabs. The method itself cannot contain any colon (':') and
is limited to alphabetic letters. All those various combinations make it
desirable that HAProxy performs the splitting itself rather than leaving it to
the user to write a complex or inaccurate regular expression.

The URI itself can have several forms :

  - A "relative URI" :

      /serv/login.php?lang=en&profile=2

    It is a complete URL without the host part. This is generally what is
    received by servers, reverse proxies and transparent proxies.

  - An "absolute URI", also called a "URL" :

      http://192.168.0.12:8080/serv/login.php?lang=en&profile=2

    It is composed of a "scheme" (the protocol name followed by '://'), a host
    name or address, optionally a colon (':') followed by a port number, then
    a relative URI beginning at the first slash ('/') after the address part.
    This is generally what proxies receive, but a server supporting HTTP/1.1
    must accept this form too.

  - a star ('*') : this form is only accepted in association with the OPTIONS
    method and is not relayable. It is used to inquiry a next hop's
    capabilities.

  - an address:port combination : 192.168.0.12:80
    This is used with the CONNECT method, which is used to establish TCP
    tunnels through HTTP proxies, generally for HTTPS, but sometimes for
    other protocols too.

In a relative URI, two sub-parts are identified. The part before the question
mark is called the "path". It is typically the relative path to static objects
on the server. The part after the question mark is called the "query string".
It is mostly used with GET requests sent to dynamic scripts and is very
specific to the language, framework or application in use.

HTTP/3 and HTTP/3 do not convey a version information with the request, so the
version is assumed to be the same as the one of the underlying protocol (i.e.
"HTTP/2"). In addition, these protocols do not send a request line as one part,
but split it into individual fields called "pseudo-headers", whose name start
with a colon, and which are conveniently reassembled by HAProxy into an
equivalent request line. For this reason, request lines found in logs may
slightly differ between HTTP/1.x and HTTP/2 or HTTP/3.

1.3.2. The request headers

The headers start at the second line. They are composed of a name at the
beginning of the line, immediately followed by a colon (':'). Traditionally,
an LWS is added after the colon but that's not required. Then come the values.
Multiple identical headers may be folded into one single line, delimiting the
values with commas, provided that their order is respected. This is commonly
encountered in the "Cookie:" field. A header may span over multiple lines if
the subsequent lines begin with an LWS. In the example in 1.3, lines 4 and 5
define a total of 3 values for the "Accept:" header. Finally, all LWS at the
beginning or at the end of a header are ignored and are not part of the value,
as per the specification.

Contrary to a common misconception, header names are not case-sensitive, and
their values are not either if they refer to other header names (such as the
"Connection:" header). In HTTP/2 and HTTP/3, header names are always sent in
lower case, as can be seen when running in debug mode. Internally, all header
names are normalized to lower case so that HTTP/1.x and HTTP/2 or HTTP/3 use
the exact same representation, and they are sent as-is on the other side. This
explains why an HTTP/1.x request typed with camel case is delivered in lower
case.

The end of the headers is indicated by the first empty line. People often say
that it's a double line feed, which is not exact, even if a double line feed
is one valid form of empty line.

Fortunately, HAProxy takes care of all these complex combinations when indexing
headers, checking values and counting them, so there is no reason to worry
about the way they could be written, but it is important not to accuse an
application of being buggy if it does unusual, valid things.

Important note:
   As suggested by RFC7231, HAProxy normalizes headers by replacing line breaks
   in the middle of headers by LWS in order to join multi-line headers. This
   is necessary for proper analysis and helps less capable HTTP parsers to work
   correctly and not to be fooled by such complex constructs.

1.4. HTTP response

An HTTP response looks very much like an HTTP request. Both are called HTTP
messages. Let's consider this HTTP response :

  Line     Contents
  number
     1     HTTP/1.1 200 OK
     2     Content-length: 350
     3     Content-Type: text/html

As a special case, HTTP supports so called "Informational responses" as status
codes 1xx. These messages are special in that they don't convey any part of the
response, they're just used as sort of a signaling message to ask a client to
continue to post its request for instance. In the case of a status 100 response
the requested information will be carried by the next non-100 response message
following the informational one. This implies that multiple responses may be
sent to a single request, and that this only works when keep-alive is enabled
(1xx messages appeared in HTTP/1.1). HAProxy handles these messages and is able
to correctly forward and skip them, and only process the next non-100 response.
As such, these messages are neither logged nor transformed, unless explicitly
state otherwise. Status 101 messages indicate that the protocol is changing
over the same connection and that HAProxy must switch to tunnel mode, just as
if a CONNECT had occurred. Then the Upgrade header would contain additional
information about the type of protocol the connection is switching to.

1.4.1. The response line

Line 1 is the "response line". It is always composed of 3 fields :

  - a version tag : HTTP/1.1
  - a status code : 200
  - a reason      : OK

The status code is always 3-digit. The first digit indicates a general status :
 - 1xx = informational message to be skipped (e.g. 100, 101)
 - 2xx = OK, content is following   (e.g. 200, 206)
 - 3xx = OK, no content following   (e.g. 302, 304)
 - 4xx = error caused by the client (e.g. 401, 403, 404)
 - 5xx = error caused by the server (e.g. 500, 502, 503)

Status codes greater than 599 must not be emitted in communications, though
certain agents may produce them in logs to report their internal statuses.
Please refer to RFC9110 for the detailed meaning of all such codes. HTTP/2 and
above do not have a version tag and use the ":status" pseudo-header to report
the status code.

The "reason" field is just a hint, but is not parsed by clients. Anything can
be found there, but it's a common practice to respect the well-established
messages. It can be composed of one or multiple words, such as "OK", "Found",
or "Authentication Required". It does not exist in HTTP/2 and above and is
not emitted there. When a response from HTTP/2 or above is transmitted to an
HTTP/1 client, HAProxy will produce such a common reason field that matches
the status code.

HAProxy may emit the following status codes by itself :

  Code  When / reason
   200  access to stats page, and when replying to monitoring requests
   301  when performing a redirection, depending on the configured code
   302  when performing a redirection, depending on the configured code
   303  when performing a redirection, depending on the configured code
   307  when performing a redirection, depending on the configured code
   308  when performing a redirection, depending on the configured code
   400  for an invalid or too large request
   401  when an authentication is required to perform the action (when
        accessing the stats page)
   403  when a request is forbidden by a "http-request deny" rule
   404  when the requested resource could not be found
   408  when the request timeout strikes before the request is complete
   410  when the requested resource is no longer available and will not
        be available again
   500  when HAProxy encounters an unrecoverable internal error, such as a
        memory allocation failure, which should never happen
   501 when HAProxy is unable to satisfy a client request because of an
       unsupported feature
   502  when the server returns an empty, invalid or incomplete response, or
        when an "http-response deny" rule blocks the response.
   503  when no server was available to handle the request, or in response to
        monitoring requests which match the "monitor fail" condition
   504  when the response timeout strikes before the server responds

The error 4xx and 5xx codes above may be customized (see "errorloc" in section
4.2). Other status codes can be emitted on purpose by specific actions (see the
"deny", "return" and "redirect" actions in section 4.3 for example).

1.4.2. The response headers

Response headers work exactly like request headers, and as such, HAProxy uses
the same parsing function for both. Please refer to paragraph 1.3.2 for more
details.

2.1. Configuration file format

HAProxy's configuration process involves 3 major sources of parameters :

  - the arguments from the command-line, which always take precedence
  - the configuration file(s), whose format is described here
  - the running process's environment, in case some environment variables are
    explicitly referenced

The configuration file follows a fairly simple hierarchical format which obey
a few basic rules:

  1. a configuration file is an ordered sequence of statements

  2. a statement is a single non-empty line before any unprotected "#" (hash)

  3. a line is a series of tokens or "words" delimited by unprotected spaces or
     tab characters

  4. the first word or sequence of words of a line is one of the keywords or
     keyword sequences listed in this document

  5. all other words are all arguments of the first one, some being well-known
     keywords listed in this document, others being values, references to other
     parts of the configuration, or expressions

  6. certain keywords delimit a section inside which only a subset of keywords
     are supported

  7. a section ends at the end of a file or on a special keyword starting a new
     section

This is all that is needed to know to write a simple but reliable configuration
generator, but this is not enough to reliably parse any configuration nor to
figure how to deal with certain corner cases.

First, there are a few consequences of the rules above. Rule 6 and 7 imply that
the keywords used to define a new section are valid everywhere and cannot have
a different meaning in a specific section. These keywords are always a single
word (as opposed to a sequence of words), and traditionally the section that
follows them is designated using the same name. For example when speaking about
the "global section", it designates the section of configuration that follows
the "global" keyword. This usage is used a lot in error messages to help locate
the parts that need to be addressed.

A number of sections create an internal object or configuration space, which
requires to be distinguished from other ones. In this case they will take an
extra word which will set the name of this particular section. For some of them
the section name is mandatory. For example "frontend foo" will create a new
section of type "frontend" named "foo". Usually a name is specific to its
section and two sections of different types may use the same name, but this is
not recommended as it tends to complexify configuration management.

A direct consequence of rule 7 is that when multiple files are read at once,
each of them must start with a new section, and the end of each file will end
a section. A file cannot contain sub-sections nor end an existing section and
start a new one.

Rule 1 mentioned that ordering matters. Indeed, some keywords create directives
that can be repeated multiple times to create ordered sequences of rules to be
applied in a certain order. For example "tcp-request" can be used to alternate
"accept" and "reject" rules on varying criteria. As such, a configuration file
processor must always preserve a section's ordering when editing a file. The
ordering of sections usually does not matter except for the global section
which must be placed before other sections, but it may be repeated if needed.
In addition, some automatic identifiers may automatically be assigned to some
of the created objects (e.g. proxies), and by reordering sections, their
identifiers will change. These ones appear in the statistics for example. As
such, the configuration below will assign "foo" ID number 1 and "bar" ID number
2, which will be swapped if the two sections are reversed:

     listen foo
         bind :80

     listen bar
         bind :81

Another important point is that according to rules 2 and 3 above, empty lines,
spaces, tabs, and comments following and unprotected "#" character are not part
of the configuration as they are just used as delimiters. This implies that the
following configurations are strictly equivalent:

         global#this is the global section
     daemon#daemonize
         frontend         foo
     mode             http   # or tcp

and:

     global
         daemon

     # this is the public web frontend
     frontend foo
         mode http

The common practice is to align to the left only the keyword that initiates a
new section, and indent (i.e. prepend a tab character or a few spaces) all
other keywords so that it's instantly visible that they belong to the same
section (as done in the second example above). Placing comments before a new
section helps the reader decide if it's the desired one. Leaving a blank line
at the end of a section also visually helps spotting the end when editing it.

Tabs are very convenient for indent but they do not copy-paste well. If spaces
are used instead, it is recommended to avoid placing too many (2 to 4) so that
editing in field doesn't become a burden with limited editors that do not
support automatic indent.

In the early days it used to be common to see arguments split at fixed tab
positions because most keywords would not take more than two arguments. With
modern versions featuring complex expressions this practice does not stand
anymore, and is not recommended.

2.2. Quoting and escaping

In modern configurations, some arguments require the use of some characters
that were previously considered as pure delimiters. In order to make this
possible, HAProxy supports character escaping by prepending a backslash ('\')
in front of the character to be escaped, weak quoting within double quotes
('"') and strong quoting within single quotes ("'").

This is pretty similar to what is done in a number of programming languages and
very close to what is commonly encountered in Bourne shell. The principle is
the following: while the configuration parser cuts the lines into words, it
also takes care of quotes and backslashes to decide whether a character is a
delimiter or is the raw representation of this character within the current
word. The escape character is then removed, the quotes are removed, and the
remaining word is used as-is as a keyword or argument for example.

If a backslash is needed in a word, it must either be escaped using itself
(i.e. double backslash) or be strongly quoted.

Escaping outside quotes is achieved by preceding a special character by a
backslash ('\'):

  \    to mark a space and differentiate it from a delimiter
  \#   to mark a hash and differentiate it from a comment
  \\   to use a backslash
  \'   to use a single quote and differentiate it from strong quoting
  \"   to use a double quote and differentiate it from weak quoting

In addition, a few non-printable characters may be emitted using their usual
C-language representation:

  \n   to insert a line feed (LF, character \x0a or ASCII 10 decimal)
  \r   to insert a carriage return (CR, character \x0d or ASCII 13 decimal)
  \t   to insert a tab (character \x09 or ASCII 9 decimal)
  \xNN to insert character having ASCII code hex NN (e.g \x0a for LF).

Weak quoting is achieved by surrounding double quotes ("") around the character
or sequence of characters to protect. Weak quoting prevents the interpretation
of:

       space or tab as a word separator
  '    single quote as a strong quoting delimiter
  #    hash as a comment start

Weak quoting permits the interpretation of environment variables (which are not
evaluated outside of quotes) by preceding them with a dollar sign ('$'). If a
dollar character is needed inside double quotes, it must be escaped using a
backslash.

Strong quoting is achieved by surrounding single quotes ('') around the
character or sequence of characters to protect. Inside single quotes, nothing
is interpreted, it's the efficient way to quote regular expressions.

As a result, here is the matrix indicating how special characters can be
entered in different contexts (unprintable characters are replaced with their
name within angle brackets). Note that some characters that may only be
represented escaped have no possible representation inside single quotes,
hence its absence there:
CharacterUnquotedWeakly quotedStrongly quoted
<TAB>\<TAB>, \x09"<TAB>", "\<TAB>", "\x09"'<TAB>'
<LF>\n, \x0a"\n", "\x0a"
<CR>\r, \x0d"\r", "\x0d"
<SPC>\<SPC>, \x20"<SPC>", "\<SPC>", "\x20"'<SPC>'
"\", \x22"\"", "\x22"'"'
#\#, \x23"#", "\#", "\x23"'#'
$$, \$, \x24"\$", "\x24"'$'
'\', \x27"'", "\'", "\x27"
\\\, \x5c"\\", "\x5c"'\'
Example:
# those are all strictly equivalent:
log-format %{+Q}o\ %t\ %s\ %{-Q}r
log-format "%{+Q}o %t %s %{-Q}r"
log-format '%{+Q}o %t %s %{-Q}r'
log-format "%{+Q}o %t"' %s %{-Q}r'
log-format "%{+Q}o %t"' %s'\ %{-Q}r
There is one particular case where a second level of quoting or escaping may be
necessary. Some keywords take arguments within parenthesis, sometimes delimited
by commas. These arguments are commonly integers or predefined words, but when
they are arbitrary strings, it may be required to perform a separate level of
escaping to disambiguate the characters that belong to the argument from the
characters that are used to delimit the arguments themselves. A pretty common
case is the "regsub" converter. It takes a regular expression in argument, and
if a closing parenthesis is needed inside, this one will require to have its
own quotes.

The keyword argument parser is exactly the same as the top-level one regarding
quotes, except that the \#, \$, and \xNN escapes are not processed. But what is
not always obvious is that the delimiters used inside must first be escaped or
quoted so that they are not resolved at the top level.

Let's take this example making use of the "regsub" converter which takes 3
arguments, one regular expression, one replacement string and one set of flags:

    # replace all occurrences of "foo" with "blah" in the path:
    http-request set-path %[path,regsub(foo,blah,g)]

Here no special quoting was necessary. But if now we want to replace either
"foo" or "bar" with "blah", we'll need the regular expression "(foo|bar)". We
cannot write:

    http-request set-path %[path,regsub((foo|bar),blah,g)]

because we would like the string to cut like this:

    http-request set-path %[path,regsub((foo|bar),blah,g)]
                                       |---------|----|-|
                                 arg1 _/         /    /
                                 arg2 __________/    /
                                 arg3 ______________/

but actually what is passed is a string between the opening and closing
parenthesis then garbage:

    http-request set-path %[path,regsub((foo|bar),blah,g)]
                                       |--------|--------|
                        arg1=(foo|bar _/        /
                    trailing garbage  _________/

The obvious solution here seems to be that the closing parenthesis needs to be
quoted, but alone this will not work, because as mentioned above, quotes are
processed by the top-level parser which will resolve them before processing
this word:

    http-request set-path %[path,regsub("(foo|bar)",blah,g)]
    ------------ -------- ----------------------------------
       word1       word2    word3=%[path,regsub((foo|bar),blah,g)]

So we didn't change anything for the argument parser at the second level which
still sees a truncated regular expression as the only argument, and garbage at
the end of the string. By escaping the quotes they will be passed unmodified to
the second level:

    http-request set-path %[path,regsub(\"(foo|bar)\",blah,g)]
    ------------ -------- ------------------------------------
       word1       word2    word3=%[path,regsub("(foo|bar)",blah,g)]
                                                |---------||----|-|
                                arg1=(foo|bar) _/          /    /
                                    arg2=blah  ___________/    /
                                        arg3=g _______________/

Another approach consists in using single quotes outside the whole string and
double quotes inside (so that the double quotes are not stripped again):

    http-request set-path '%[path,regsub("(foo|bar)",blah,g)]'
    ------------ --------  ----------------------------------
       word1       word2    word3=%[path,regsub("(foo|bar)",blah,g)]
                                                |---------||----|-|
                                arg1=(foo|bar) _/          /    /
                                          arg2 ___________/    /
                                          arg3 _______________/

When using regular expressions, it can happen that the dollar ('$') character
appears in the expression or that a backslash ('\') is used in the replacement
string. In this case these ones will also be processed inside the double quotes
thus single quotes are preferred (or double escaping). Example:

    http-request set-path '%[path,regsub("^/(here)(/|$)","my/\1",g)]'
    ------------ --------  -----------------------------------------
       word1       word2    word3=%[path,regsub("^/(here)(/|$)","my/\1",g)]
                                                |-------------| |-----||-|
                              arg1=(here)(/|$) _/               /      /
                                    arg2=my/\1 ________________/      /
                                          arg3 ______________________/

Remember that backslashes are not escape characters within single quotes and
that the whole word above is already protected against them using the single
quotes. Conversely, if double quotes had been used around the whole expression,
single the dollar character and the backslashes would have been resolved at top
level, breaking the argument contents at the second level.

Unfortunately, since single quotes can't be escaped inside of strong quoting,
if you need to include single quotes in your argument, you will need to escape
or quote them twice. There are a few ways to do this:

    http-request set-var(txn.foo) str("\\'foo\\'")
    http-request set-var(txn.foo) str(\"\'foo\'\")
    http-request set-var(txn.foo) str(\\\'foo\\\')

When in doubt, simply do not use quotes anywhere, and start to place single or
double quotes around arguments that require a comma or a closing parenthesis,
and think about escaping these quotes using a backslash if the string contains
a dollar or a backslash. Again, this is pretty similar to what is used under
a Bourne shell when double-escaping a command passed to "eval". For API writers
the best is probably to place escaped quotes around each and every argument,
regardless of their contents. Users will probably find that using single quotes
around the whole expression and double quotes around each argument provides
more readable configurations.

2.3. Environment variables

HAProxy's configuration supports environment variables. Those variables are
interpreted only within double quotes. Variables are expanded during the
configuration parsing. Variable names must be preceded by a dollar ("$") and
optionally enclosed with braces ("{}") similarly to what is done in Bourne
shell. Variable names can contain alphanumerical characters or the character
underscore ("_") but should not start with a digit. If the variable contains a
list of several values separated by spaces, it can be expanded as individual
arguments by enclosing the variable with braces and appending the suffix '[*]'
before the closing brace. It is also possible to specify a default value to
use when the variable is not set, by appending that value after a dash '-'
next to the variable name. Note that the default value only replaces non
existing variables, not empty ones.
Example:
bind "fd@${FD_APP1}"

log "${LOCAL_SYSLOG-127.0.0.1}:514" local0 notice  # send to local server

user "$HAPROXY_USER"
Some variables are defined by HAProxy, they can be used in the configuration
file, or could be inherited by a program (See 3.7. Programs):

* HAPROXY_LOCALPEER: defined at the startup of the process which contains the
  name of the local peer. (See "-L" in the management guide.)

* HAPROXY_CFGFILES: list of the configuration files loaded by HAProxy,
  separated by semicolons. Can be useful in the case you specified a
  directory.

* HAPROXY_HTTP_LOG_FMT: contains the value of the default HTTP log format as
  defined in section 8.2.3 "HTTP log format". It can be used to override the
  default log format without having to copy the whole original definition.
Example:
# Add the rule that gave the final verdict to the log
log-format "${HAPROXY_TCP_LOG_FMT} lr=last_rule_file:last_rule_line"
* HAPROXY_HTTPS_LOG_FMT: similar to HAPROXY_HTTP_LOG_FMT but for HTTPS log
  format as defined in section 8.2.4 "HTTPS log format".

* HAPROXY_TCP_LOG_FMT: similar to HAPROXY_HTTP_LOG_FMT but for TCP log format
  as defined in section 8.2.2 "TCP log format".

* HAPROXY_MWORKER: In master-worker mode, this variable is set to 1.

* HAPROXY_CLI: configured listeners addresses of the stats socket for every
  processes, separated by semicolons.

* HAPROXY_MASTER_CLI: In master-worker mode, listeners addresses of the master
  CLI, separated by semicolons.

* HAPROXY_STARTUP_VERSION: contains the version used to start, in master-worker
  mode this is the version which was used to start the master, even after
  updating the binary and reloading.

* HAPROXY_BRANCH: contains the HAProxy branch version (such as "2.8"). It does
  not contain the full version number. It can be useful in case of migration
  if resources (such as maps or certificates) are in a path containing the
  branch number.

In addition, some pseudo-variables are internally resolved and may be used as
regular variables. Pseudo-variables always start with a dot ('.'), and are the
only ones where the dot is permitted. The current list of pseudo-variables is:

* .FILE: the name of the configuration file currently being parsed.

* .LINE: the line number of the configuration file currently being parsed,
  starting at one.

* .SECTION: the name of the section currently being parsed, or its type if the
  section doesn't have a name (e.g. "global"), or an empty string before the
  first section.

These variables are resolved at the location where they are parsed. For example
if a ".LINE" variable is used in a "log-format" directive located in a defaults
section, its line number will be resolved before parsing and compiling the
"log-format" directive, so this same line number will be reused by subsequent
proxies.

This way it is possible to emit information to help locate a rule in variables,
logs, error statuses, health checks, header values, or even to use line numbers
to name some config objects like servers for example.

See also "external-check command" for other variables.

2.4. Conditional blocks

It may sometimes be convenient to be able to conditionally enable or disable
some arbitrary parts of the configuration, for example to enable/disable SSL or
ciphers, enable or disable some pre-production listeners without modifying the
configuration, or adjust the configuration's syntax to support two distinct
versions of HAProxy during a migration.. HAProxy brings a set of nestable
preprocessor-like directives which allow to integrate or ignore some blocks of
text. These directives must be placed on their own line and they act on the
lines that follow them. Two of them support an expression, the other ones only
switch to an alternate block or end a current level. The 4 following directives
are defined to form conditional blocks:

  - .if <condition>
  - .elif <condition>
  - .else
  - .endif

The ".if" directive nests a new level, ".elif" stays at the same level, ".else"
as well, and ".endif" closes a level. Each ".if" must be terminated by a
matching ".endif". The ".elif" may only be placed after ".if" or ".elif", and
there is no limit to the number of ".elif" that may be chained. There may be
only one ".else" per ".if" and it must always be after the ".if" or the last
".elif" of a block.

Comments may be placed on the same line if needed after a '#', they will be
ignored. The directives are tokenized like other configuration directives, and
as such it is possible to use environment variables in conditions.

Conditions can also be evaluated on startup with the -cc parameter.
See "3. Starting HAProxy" in the management doc.

The conditions are either an empty string (which then returns false), or an
expression made of any combination of:

  - the integer zero ('0'), always returns "false"
  - a non-nul integer (e.g. '1'), always returns "true".
  - a predicate optionally followed by argument(s) in parenthesis.
  - a condition placed between a pair of parenthesis '(' and ')'
  - an exclamation mark ('!') preceding any of the non-empty elements above,
    and which will negate its status.
  - expressions combined with a logical AND ('&&'), which will be evaluated
    from left to right until one returns false
  - expressions combined with a logical OR ('||'), which will be evaluated
    from right to left until one returns true

Note that like in other languages, the AND operator has precedence over the OR
operator, so that "A && B || C && D" evalues as "(A && B) || (C && D)".

The list of currently supported predicates is the following:

  - defined(<name>)       : returns true if an environment variable <name>
                            exists, regardless of its contents

  - feature(<name>)       : returns true if feature <name> is listed as present
                            in the features list reported by "haproxy -vv"
                            (which means a <name> appears after a '+')

  - streq(<str1>,<str2>)  : returns true only if the two strings are equal
  - strneq(<str1>,<str2>) : returns true only if the two strings differ
  - strstr(<str1>,<str2>) : returns true only if the second string is found in the first one

  - version_atleast(<ver>): returns true if the current haproxy version is
                            at least as recent as <ver> otherwise false. The
                            version syntax is the same as shown by "haproxy -v"
                            and missing components are assumed as being zero.

  - version_before(<ver>) : returns true if the current haproxy version is
                            strictly older than <ver> otherwise false. The
                            version syntax is the same as shown by "haproxy -v"
                            and missing components are assumed as being zero.

  - enabled(<opt>)        : returns true if the option <opt> is enabled at
                            run-time. Only a subset of options are supported:
                                POLL, EPOLL, KQUEUE, EVPORTS, SPLICE,
                                GETADDRINFO, REUSEPORT, FAST-FORWARD,
                                SERVER-SSL-VERIFY-NONE
Example:
.if defined(HAPROXY_MWORKER)
    listen mwcli_px
       bind :1111
       ...
.endif

.if strneq("$SSL_ONLY",yes)
       bind :80
.endif

.if streq("$WITH_SSL",yes)
  .if feature(OPENSSL)
       bind :443 ssl crt ...
  .endif
.endif

.if feature(OPENSSL) && (streq("$WITH_SSL",yes) || streq("$SSL_ONLY",yes))
       bind :443 ssl crt ...
.endif

.if version_atleast(2.4-dev19)
    profiling.memory on
.endif

.if !feature(OPENSSL)
    .alert "SSL support is mandatory"
.endif
Four other directives are provided to report some status:

  - .diag "message"    : emit this message only when in diagnostic mode (-dD)
  - .notice "message"  : emit this message at level NOTICE
  - .warning "message" : emit this message at level WARNING
  - .alert "message"   : emit this message at level ALERT

Messages emitted at level WARNING may cause the process to fail to start if the
"strict-mode" is enabled. Messages emitted at level ALERT will always cause a
fatal error. These can be used to detect some inappropriate conditions and
provide advice to the user.
Example:
.if "${A}"
  .if "${B}"
     .notice "A=1, B=1"
  .elif "${C}"
     .notice "A=1, B=0, C=1"
  .elif "${D}"
     .warning "A=1, B=0, C=0, D=1"
  .else
     .alert "A=1, B=0, C=0, D=0"
  .endif
.else
     .notice "A=0"
.endif

.diag "WTA/2021-05-07: replace 'redirect' with 'return' after switch to 2.4"
      http-request redirect location /goaway if ABUSE

2.5. Time format

Some parameters involve values representing time, such as timeouts. These
values are generally expressed in milliseconds (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are :

  - us : microseconds. 1 microsecond = 1/1000000 second
  - ms : milliseconds. 1 millisecond = 1/1000 second. This is the default.
  - s  : seconds. 1s = 1000ms
  - m  : minutes. 1m = 60s = 60000ms
  - h  : hours.   1h = 60m = 3600s = 3600000ms
  - d  : days.    1d = 24h = 1440m = 86400s = 86400000ms

2.6. Size format

Some parameters involve values representing size, such as bandwidth limits.
These values are generally expressed in bytes (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are case insensitive :

  - k : kilobytes. 1 kilobyte = 1024 bytes
  - m : megabytes. 1 megabyte = 1048576 bytes
  - g : gigabytes. 1 gigabyte = 1073741824 bytes

Both time and size formats require integers, decimal notation is not allowed.

2.7. Name format for maps and ACLs

It is possible to use a list of pattern for maps or ACLs. A list of pattern is
identified by its name and may be used at different places in the
configuration. List of pattern are split on three categories depending on
the name format:

  * Lists of pattern based on regular files: It is the default case. The
    filename, absolute or relative, is used as name. The file must exist
    otherwise an error is triggered. But it may be empty. The "file@" prefix
    may also be specified but it is not part of the name identifying the
    list. A filename, with or without the prefix, references the same list of
    pattern.

  * Lists of pattern based on optional files: The filename must be preceded by
    "opt@" prefix. The file existence is optional. If the file exists, its
    content is loaded but no error is reported if not. The prefix is not part
    of the name identifying the list. It means, for a given filename, Optional
    files and regular files reference the same list of pattern.

  * Lists of pattern based on virtual files: The name is just an identified. It
    is not a reference to any file. "virt@" prefix must be used. It is part of
    the name. Thus it cannot be mixed with other kind of lists.

Virtual files are useful when patterns are fully dynamically managed with no
patterns on startup and on reload. Optional files may be used under the same
conditions. But patterns can be dumped in the file, via an external script based
on the "show map" CLI command for instance. This way, it is possible to keep
patterns on reload.

Note: Even if it is unlikely, it means no regular file starting with "file@",
      "opt@" or "virt@" can be loaded, except by adding "./" explicitly in
      front of the filename (for instance "file@./virt@map").

2.8. Examples

    # Simple configuration for an HTTP proxy listening on port 80 on all
    # interfaces and forwarding requests to a single backend "servers" with a
    # single server "server1" listening on 127.0.0.1:8000
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    frontend http-in
        bind *:80
        default_backend servers

    backend servers
        server server1 127.0.0.1:8000 maxconn 32


    # The same configuration defined with a single listen block. Shorter but
    # less expressive, especially in HTTP mode.
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    listen http-in
        bind *:80
        server server1 127.0.0.1:8000 maxconn 32


Assuming haproxy is in $PATH, test these configurations in a shell with:

    $ sudo haproxy -f configuration.conf -c
Parameters in the "global" section are process-wide and often OS-specific. They
are generally set once for all and do not need being changed once correct. Some
of them have command-line equivalents.

The following keywords are supported in the "global" section :

 * Process management and security
   - 51degrees-allow-unmatched
   - 51degrees-cache-size
   - 51degrees-data-file
   - 51degrees-difference
   - 51degrees-drift
   - 51degrees-property-name-list
   - 51degrees-property-separator
   - 51degrees-use-performance-graph
   - 51degrees-use-predictive-graph
   - ca-base
   - chroot
   - cluster-secret
   - cpu-map
   - crt-base
   - daemon
   - default-path
   - description
   - deviceatlas-json-file
   - deviceatlas-log-level
   - deviceatlas-properties-cookie
   - deviceatlas-separator
   - expose-experimental-directives
   - external-check
   - fd-hard-limit
   - gid
   - grace
   - group
   - h1-accept-payload-with-any-method
   - h1-case-adjust
   - h1-case-adjust-file
   - h2-workaround-bogus-websocket-clients
   - hard-stop-after
   - insecure-fork-wanted
   - insecure-setuid-wanted
   - issuers-chain-path
   - localpeer
   - log
   - log-send-hostname
   - log-tag
   - lua-load
   - lua-load-per-thread
   - lua-prepend-path
   - mworker-max-reloads
   - nbthread
   - node
   - numa-cpu-mapping
   - pidfile
   - pp2-never-send-local
   - presetenv
   - prealloc-fd
   - resetenv
   - set-dumpable
   - set-var
   - setenv
   - ssl-default-bind-ciphers
   - ssl-default-bind-ciphersuites
   - ssl-default-bind-client-sigalgs
   - ssl-default-bind-curves
   - ssl-default-bind-options
   - ssl-default-bind-sigalgs
   - ssl-default-server-ciphers
   - ssl-default-server-ciphersuites
   - ssl-default-server-client-sigalgs
   - ssl-default-server-curves
   - ssl-default-server-options
   - ssl-default-server-sigalgs
   - ssl-dh-param-file
   - ssl-propquery
   - ssl-provider
   - ssl-provider-path
   - ssl-server-verify
   - ssl-skip-self-issued-ca
   - stats
   - strict-limits
   - uid
   - ulimit-n
   - unix-bind
   - unsetenv
   - user
   - wurfl-cache-size
   - wurfl-data-file
   - wurfl-information-list
   - wurfl-information-list-separator

 * Performance tuning
   - busy-polling
   - max-spread-checks
   - maxcompcpuusage
   - maxcomprate
   - maxconn
   - maxconnrate
   - maxpipes
   - maxsessrate
   - maxsslconn
   - maxsslrate
   - maxzlibmem
   - no-memory-trimming
   - noepoll
   - noevports
   - nogetaddrinfo
   - nokqueue
   - nopoll
   - noreuseport
   - nosplice
   - profiling.tasks
   - server-state-base
   - server-state-file
   - spread-checks
   - ssl-engine
   - ssl-mode-async
   - tune.applet.zero-copy-forwarding
   - tune.buffers.limit
   - tune.buffers.reserve
   - tune.bufsize
   - tune.comp.maxlevel
   - tune.disable-fast-forward
   - tune.disable-zero-copy-forwarding
   - tune.events.max-events-at-once
   - tune.fail-alloc
   - tune.fd.edge-triggered
   - tune.h1.zero-copy-fwd-recv
   - tune.h1.zero-copy-fwd-send
   - tune.h2.be.initial-window-size
   - tune.h2.be.max-concurrent-streams
   - tune.h2.fe.initial-window-size
   - tune.h2.fe.max-concurrent-streams
   - tune.h2.fe.max-total-streams
   - tune.h2.header-table-size
   - tune.h2.initial-window-size
   - tune.h2.max-concurrent-streams
   - tune.h2.max-frame-size
   - tune.h2.zero-copy-fwd-send
   - tune.http.cookielen
   - tune.http.logurilen
   - tune.http.maxhdr
   - tune.idle-pool.shared
   - tune.idletimer
   - tune.lua.forced-yield
   - tune.lua.maxmem
   - tune.lua.service-timeout
   - tune.lua.session-timeout
   - tune.lua.task-timeout
   - tune.lua.log.loggers
   - tune.lua.log.stderr
   - tune.max-checks-per-thread
   - tune.maxaccept
   - tune.maxpollevents
   - tune.maxrewrite
   - tune.memory.hot-size
   - tune.pattern.cache-size
   - tune.peers.max-updates-at-once
   - tune.pipesize
   - tune.pool-high-fd-ratio
   - tune.pool-low-fd-ratio
   - tune.pt.zero-copy-forwarding
   - tune.quic.frontend.conn-tx-buffers.limit
   - tune.quic.frontend.max-idle-timeout
   - tune.quic.frontend.max-streams-bidi
   - tune.quic.max-frame-loss
   - tune.quic.reorder-ratio
   - tune.quic.retry-threshold
   - tune.quic.socket-owner
   - tune.quic.zero-copy-fwd-send
   - tune.rcvbuf.backend
   - tune.rcvbuf.client
   - tune.rcvbuf.frontend
   - tune.rcvbuf.server
   - tune.recv_enough
   - tune.runqueue-depth
   - tune.sched.low-latency
   - tune.sndbuf.backend
   - tune.sndbuf.client
   - tune.sndbuf.frontend
   - tune.sndbuf.server
   - tune.stick-counters
   - tune.ssl.cachesize
   - tune.ssl.capture-buffer-size
   - tune.ssl.capture-cipherlist-size (deprecated)
   - tune.ssl.default-dh-param
   - tune.ssl.force-private-cache
   - tune.ssl.hard-maxrecord
   - tune.ssl.keylog
   - tune.ssl.lifetime
   - tune.ssl.maxrecord
   - tune.ssl.ssl-ctx-cache-size
   - tune.ssl.ocsp-update.maxdelay
   - tune.ssl.ocsp-update.mindelay
   - tune.vars.global-max-size
   - tune.vars.proc-max-size
   - tune.vars.reqres-max-size
   - tune.vars.sess-max-size
   - tune.vars.txn-max-size
   - tune.zlib.memlevel
   - tune.zlib.windowsize

 * Debugging
   - anonkey
   - quiet
   - zero-warning

 * HTTPClient
   - httpclient.resolvers.disabled
   - httpclient.resolvers.id
   - httpclient.resolvers.prefer
   - httpclient.retries
   - httpclient.ssl.ca-file
   - httpclient.ssl.verify
   - httpclient.timeout.connect

3.1. Process management and security

The path of the 51Degrees data file to provide device detection services. The
file should be unzipped and accessible by HAProxy with relevant permissions.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.
A list of 51Degrees property names to be load from the dataset. A full list
of names is available on the 51Degrees website:
https://51degrees.com/resources/property-dictionary

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.
A char that will be appended to every property value in a response header
containing 51Degrees results. If not set that will be set as ','.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.
Sets the size of the 51Degrees converter cache to <number> entries. This
is an LRU cache which reminds previous device detections and their results.
By default, this cache is disabled.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.
Enables ('on') or disables ('off') the use of the performance graph in
the detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.
Enables ('on') or disables ('off') the use of the predictive graph in
the detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.
Sets the drift value that a detection can allow.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.
Sets the difference value that a detection can allow.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.
Enables ('on') or disables ('off') the use of unmatched nodes in the
detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.
ca-base <dir>
Assigns a default directory to fetch SSL CA certificates and CRLs from when a
relative path is used with "ca-file", "ca-verify-file" or "crl-file"
directives. Absolute locations specified in "ca-file", "ca-verify-file" and
"crl-file" prevail and ignore "ca-base".
chroot <jail dir>
Changes current directory to <jail dir> and performs a chroot() there before
dropping privileges. This increases the security level in case an unknown
vulnerability would be exploited, since it would make it very hard for the
attacker to exploit the system. This only works when the process is started
with superuser privileges. It is important to ensure that <jail_dir> is both
empty and non-writable to anyone.
Define a time window during which idle connections and active connections
closing is spread in case of soft-stop. After a SIGUSR1 is received and the
grace period is over (if any), the idle connections will all be closed at
once if this option is not set, and active HTTP or HTTP2 connections will be
ended after the next request is received, either by appending a "Connection:
close" line to the HTTP response, or by sending a GOAWAY frame in case of
HTTP2. When this option is set, connection closing will be spread over this
set <time>.
If the close-spread-time is set to "infinite", active connection closing
during a soft-stop will be disabled. The "Connection: close" header will not
be added to HTTP responses (or GOAWAY for HTTP2) anymore and idle connections
will only be closed once their timeout is reached (based on the various
timeouts set in the configuration).
Arguments :
<time>  is a time window (by default in milliseconds) during which
        connection closing will be spread during a soft-stop operation, or
        "infinite" if active connection closing should be disabled.
It is recommended to set this setting to a value lower than the one used in
the "hard-stop-after" option if this one is used, so that all connections
have a chance to gracefully close before the process stops.
Define an ASCII string secret shared between several nodes belonging to the
same cluster. It could be used for different usages. It is at least used to
derive stateless reset tokens for all the QUIC connections instantiated by
this process. This is also the case to derive secrets used to encrypt Retry
tokens.

If this parameter is not set, a random value will be selected on process
startup. This allows to use features which rely on it, albeit with some
limitations.
cpu-map [auto:]<thread-group>[/<thread-set>] <cpu-set>[,...] [...]
On some operating systems, it is possible to bind a thread group or a thread
to a specific CPU set. This means that the designated threads will never run
on other CPUs. The "cpu-map" directive specifies CPU sets for individual
threads or thread groups. The first argument is a thread group range,
optionally followed by a thread set. These ranges have the following format:

    all | odd | even | number[-[number]]

<number> must be a number between 1 and 32 or 64, depending on the machine's
word size. Any group IDs above 'thread-groups' and any thread IDs above the
machine's word size are ignored. All thread numbers are relative to the group
they belong to. It is possible to specify a range with two such number
delimited by a dash ('-'). It also is possible to specify all threads at once
using "all", only odd numbers using "odd" or even numbers using "even", just
like with the "thread" bind directive. The second and forthcoming arguments
are CPU sets. Each CPU set is either a unique number starting at 0 for the
first CPU or a range with two such numbers delimited by a dash ('-'). These
CPU numbers and ranges may be repeated by delimiting them with commas or by
passing more ranges as new arguments on the same line. Outside of Linux and
BSD operating systems, there may be a limitation on the maximum CPU index to
either 31 or 63. Multiple "cpu-map" directives may be specified, but each
"cpu-map" directive will replace the previous ones when they overlap.

Ranges can be partially defined. The higher bound can be omitted. In such
case, it is replaced by the corresponding maximum value, 32 or 64 depending
on the machine's word size.

The prefix "auto:" can be added before the thread set to let HAProxy
automatically bind a set of threads to a CPU by incrementing threads and
CPU sets. To be valid, both sets must have the same size. No matter the
declaration order of the CPU sets, it will be bound from the lowest to the
highest bound. Having both a group and a thread range with the "auto:"
prefix is not supported. Only one range is supported, the other one must be
a fixed number.

Note that group ranges are supported for historical reasons. Nowadays, a lone
number designates a thread group and must be 1 if thread-groups are not used,
and specifying a thread range or number requires to prepend "1/" in front of
it if thread groups are not used. Finally, "1" is strictly equivalent to
"1/all" and designates all threads in the group.
Examples:
cpu-map 1/all 0-3 # bind all threads of the first group on the
                  # first 4 CPUs

cpu-map 1/1- 0-   # will be replaced by "cpu-map 1/1-64 0-63"
                  # or "cpu-map 1/1-32 0-31" depending on the machine's
                  # word size.

# all these lines bind thread 1 to the cpu 0, the thread 2 to cpu 1
# and so on.
cpu-map auto:1/1-4   0-3
cpu-map auto:1/1-4   0-1 2-3
cpu-map auto:1/1-4   3 2 1 0
cpu-map auto:1/1-4   3,2,1,0

# bind each thread to exactly one CPU using all/odd/even keyword
cpu-map auto:1/all   0-63
cpu-map auto:1/even  0-31
cpu-map auto:1/odd   32-63

# invalid cpu-map because thread and CPU sets have different sizes.
cpu-map auto:1/1-4   0    # invalid
cpu-map auto:1/1     0-3  # invalid

# map 40 threads of those 4 groups to individual CPUs
cpu-map auto:1/1-10   0-9
cpu-map auto:2/1-10   10-19
cpu-map auto:3/1-10   20-29
cpu-map auto:4/1-10   30-39

# Map 80 threads to one physical socket and 80 others to another socket
# without forcing assignment. These are split into 4 groups since no
# group may have more than 64 threads.
cpu-map 1/1-40   0-39,80-119    # node0, siblings 0 & 1
cpu-map 2/1-40   0-39,80-119
cpu-map 3/1-40   40-79,120-159  # node1, siblings 0 & 1
cpu-map 4/1-40   40-79,120-159
crt-base <dir>
Assigns a default directory to fetch SSL certificates from when a relative
path is used with "crtfile" or "crt" directives. Absolute locations specified
prevail and ignore "crt-base".
Makes the process fork into background. This is the recommended mode of
operation. It is equivalent to the command line "-D" argument. It can be
disabled by the command line "-db" argument. This option is ignored in
systemd mode.
default-path { current | config | parent | origin <path> }
By default HAProxy loads all files designated by a relative path from the
location the process is started in. In some circumstances it might be
desirable to force all relative paths to start from a different location
just as if the process was started from such locations. This is what this
directive is made for. Technically it will perform a temporary chdir() to
the designated location while processing each configuration file, and will
return to the original directory after processing each file. It takes an
argument indicating the policy to use when loading files whose path does
not start with a slash ('/'):
  - "current" indicates that all relative files are to be loaded from the
    directory the process is started in ; this is the default.

  - "config" indicates that all relative files should be loaded from the
    directory containing the configuration file. More specifically, if the
    configuration file contains a slash ('/'), the longest part up to the
    last slash is used as the directory to change to, otherwise the current
    directory is used. This mode is convenient to bundle maps, errorfiles,
    certificates and Lua scripts together as relocatable packages. When
    multiple configuration files are loaded, the directory is updated for
    each of them.

  - "parent" indicates that all relative files should be loaded from the
    parent of the directory containing the configuration file. More
    specifically, if the configuration file contains a slash ('/'), ".."
    is appended to the longest part up to the last slash is used as the
    directory to change to, otherwise the directory is "..". This mode is
    convenient to bundle maps, errorfiles,  certificates and Lua scripts
    together as relocatable packages, but where each part is located in a
    different subdirectory (e.g. "config/", "certs/", "maps/", ...).

  - "origin" indicates that all relative files should be loaded from the
    designated (mandatory) path. This may be used to ease management of
    different HAProxy instances running in parallel on a system, where each
    instance uses a different prefix but where the rest of the sections are
    made easily relocatable.

Each "default-path" directive instantly replaces any previous one and will
possibly result in switching to a different directory. While this should
always result in the desired behavior, it is really not a good practice to
use multiple default-path directives, and if used, the policy ought to remain
consistent across all configuration files.

Warning: some configuration elements such as maps or certificates are
uniquely identified by their configured path. By using a relocatable layout,
it becomes possible for several of them to end up with the same unique name,
making it difficult to update them at run time, especially when multiple
configuration files are loaded from different directories. It is essential to
observe a strict collision-free file naming scheme before adopting relative
paths. A robust approach could consist in prefixing all files names with
their respective site name, or in doing so at the directory level.
Add a text that describes the instance.

Please note that it is required to escape certain characters (# for example)
and this text is inserted into a html page so you should avoid using
"<" and ">" characters.
Sets the path of the DeviceAtlas JSON data file to be loaded by the API.
The path must be a valid JSON data file and accessible by HAProxy process.
Sets the level of information returned by the API. This directive is
optional and set to 0 by default if not set.
Sets the client cookie's name used for the detection if the DeviceAtlas
Client-side component was used during the request. This directive is optional
and set to DAPROPS by default if not set.
Sets the character separator for the API properties results. This directive
is optional and set to | by default if not set.
This statement must appear before using directives tagged as experimental or
the config file will be rejected.
external-check [preserve-env]
Allows the use of an external agent to perform health checks. This is
disabled by default as a security precaution, and even when enabled, checks
may still fail unless "insecure-fork-wanted" is enabled as well. If the
program launched makes use of a setuid executable (it should really not),
you may also need to set "insecure-setuid-wanted" in the global section.
By default, the checks start with a clean environment which only contains
variables defined in the "external-check" command in the backend section. It
may sometimes be desirable to preserve the environment though, for example
when complex scripts retrieve their extra paths or information there. This
can be done by appending the "preserve-env" keyword. In this case however it
is strongly advised not to run a setuid nor as a privileged user, as this
exposes the check program to potential attacks. See "option external-check",
and "insecure-fork-wanted", and "insecure-setuid-wanted" for extra details.
fd-hard-limit <number>
Sets an upper bound to the maximum number of file descriptors that the
process will use, regardless of system limits. While "ulimit-n" and "maxconn"
may be used to enforce a value, when they are not set, the process will be
limited to the hard limit of the RLIMIT_NOFILE setting as reported by
"ulimit -n -H". But some modern operating systems are now allowing extremely
large values here (in the order of 1 billion), which will consume way too
much RAM for regular usage. The fd-hard-limit setting is provided to enforce
a possibly lower bound to this limit. This means that it will always respect
the system-imposed limits when they are below <number> but the specified
value will be used if system-imposed limits are higher. In the example below,
no other setting is specified and the maxconn value will automatically adapt
to the lower of "fd-hard-limit" and the system-imposed limit:

    global
        # use as many FDs as possible but no more than 50000
        fd-hard-limit 50000
gid <number>
Changes the process's group ID to <number>. It is recommended that the group
ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with a user belonging to this group, or with superuser privileges.
Note that if HAProxy is started from a user having supplementary groups, it
will only be able to drop these groups if started with superuser privileges.
See also "group" and "uid".
grace <time>
Defines a delay between SIGUSR1 and real soft-stop.
Arguments :
<time>  is an extra delay (by default in milliseconds) after receipt of the
        SIGUSR1 signal that will be waited for before proceeding with the
        soft-stop operation.
This is used for compatibility with legacy environments where the haproxy
process needs to be stopped but some external components need to detect the
status before listeners are unbound. The principle is that the internal
"stopping" variable (which is reported by the "stopping" sample fetch
function) will be turned to true, but listeners will continue to accept
connections undisturbed, until the delay expires, after what the regular
soft-stop will proceed. This must not be used with processes that are
reloaded, or this will prevent the old process from unbinding, and may
prevent the new one from starting, or simply cause trouble.
Example:
global
  grace 10s

# Returns 200 OK until stopping is set via SIGUSR1
frontend ext-check
  bind :9999
  monitor-uri /ext-check
  monitor fail if { stopping }
Please note that a more flexible and durable approach would instead consist
for an orchestration system in setting a global variable from the CLI, use
that variable to respond to external checks, then after a delay send the
SIGUSR1 signal.
Example:
# Returns 200 OK until proc.stopping is set to non-zero. May be done
# from HTTP using set-var(proc.stopping) or from the CLI using:
# > set var proc.stopping int(1)
frontend ext-check
  bind :9999
  monitor-uri /ext-check
  monitor fail if { var(proc.stopping) -m int gt 0 }
group <group name>
Similar to "gid" but uses the GID of group name <group name> from /etc/group.
See also "gid" and "user".
Does not reject HTTP/1.0 GET/HEAD/DELETE requests with a payload.

While It is explicitly allowed in HTTP/1.1, HTTP/1.0 is not clear on this
point and some old servers don't expect any payload and never look for body
length (via Content-Length or Transfer-Encoding headers). It means that some
intermediaries may properly handle the payload for HTTP/1.0 GET/HEAD/DELETE
requests, while some others may totally ignore it. That may lead to security
issues because a request smuggling attack is possible. Thus, by default,
HAProxy rejects HTTP/1.0 GET/HEAD/DELETE requests with a payload.

However, it may be an issue with some old clients. In this case, this global
option may be set.
h1-case-adjust <from> <to>
Defines the case adjustment to apply, when enabled, to the header name
<from>, to change it to <to> before sending it to HTTP/1 clients or
servers. <from> must be in lower case, and <from> and <to> must not differ
except for their case. It may be repeated if several header names need to be
adjusted. Duplicate entries are not allowed. If a lot of header names have to
be adjusted, it might be more convenient to use "h1-case-adjust-file".
Please note that no transformation will be applied unless "option
h1-case-adjust-bogus-client" or "option h1-case-adjust-bogus-server" is
specified in a proxy.

There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

Applications which fail to properly process requests or responses may require
to temporarily use such workarounds to adjust header names sent to them for
the time it takes the application to be fixed. Please note that an
application which requires such workarounds might be vulnerable to content
smuggling attacks and must absolutely be fixed.
Example:
global
  h1-case-adjust content-length Content-Length
See "h1-case-adjust-file", "option h1-case-adjust-bogus-client" and
"option h1-case-adjust-bogus-server".
Defines a file containing a list of key/value pairs used to adjust the case
of some header names before sending them to HTTP/1 clients or servers. The
file <hdrs-file> must contain 2 header names per line. The first one must be
in lower case and both must not differ except for their case. Lines which
start with '#' are ignored, just like empty lines. Leading and trailing tabs
and spaces are stripped. Duplicate entries are not allowed. Please note that
no transformation will be applied unless "option h1-case-adjust-bogus-client"
or "option h1-case-adjust-bogus-server" is specified in a proxy.

If this directive is repeated, only the last one will be processed.  It is an
alternative to the directive "h1-case-adjust" if a lot of header names need
to be adjusted. Please read the risks associated with using this.

See "h1-case-adjust", "option h1-case-adjust-bogus-client" and
"option h1-case-adjust-bogus-server".
This disables the announcement of the support for h2 websockets to clients.
This can be use to overcome clients which have issues when implementing the
relatively fresh RFC8441, such as Firefox 88. To allow clients to
automatically downgrade to http/1.1 for the websocket tunnel, specify h2
support on the bind line using "alpn" without an explicit "proto" keyword. If
this statement was previously activated, this can be disabled by prefixing
the keyword with "no'.
Defines the maximum time allowed to perform a clean soft-stop.
Arguments :
<time>  is the maximum time (by default in milliseconds) for which the
        instance will remain alive when a soft-stop is received via the
        SIGUSR1 signal.
This may be used to ensure that the instance will quit even if connections
remain opened during a soft-stop (for example with long timeouts for a proxy
in tcp mode). It applies both in TCP and HTTP mode.
Example:
global
  hard-stop-after 30s
http-err-codes [+-]<range>[,...] [...]
Replace, reduce or extend the list of status codes that define an error as
considered by the termination codes and the "http_err_cnt" counter in stick
tables. The default range for errors is 400 to 499, but in certain contexts
some users prefer to exclude specific codes, especially when tracking client
errors (e.g. 404 on systems with dynamically generated contents). See also
"http-fail-codes" and "http_err_cnt".

A range specified without '+' nor '-' redefines the existing range to the new
one. A range starting with '+' extends the existing range to also include the
specified one, which may or may not overlap with the existing one. A range
starting with '-' removes the specified range from the existing one. A range
consists in a number from 100 to 599, optionally followed by "-" followed by
another number greater than or equal to the first one to indicate the high
boundary of the range. Multiple ranges may be delimited by commas for a same
add/del/ replace operation.
Example:
http-err-codes 400,402-444,446-480,490   # sets exactly these codes
http-err-codes 400-499 -450 +500         # sets 400 to 500 except 450
http-err-codes -450-459                  # removes 450 to 459 from range
http-err-codes +501,505                  # adds 501 and 505 to range
http-fail-codes [+-]<range>[,...] [...]
Replace, reduce or extend the list of status codes that define a failure as
considered by the termination codes and the "http_fail_cnt" counter in stick
tables. The default range for failures is 500 to 599 except 501 and 505 which
can be triggered by clients, and normally indicate a failure from the server
to process the request. Some users prefer to exclude certain codes in certain
contexts where it is known they're not relevant, such as 500 in certain SOAP
environments as it doesn't translate a server fault there. The syntax is
exactly the same as for http-err-codes above. See also "http-err-codes" and
"http_fail_cnt".
By default HAProxy tries hard to prevent any thread and process creation
after it starts. Doing so is particularly important when using Lua files of
uncertain origin, and when experimenting with development versions which may
still contain bugs whose exploitability is uncertain. And generally speaking
it's good hygiene to make sure that no unexpected background activity can be
triggered by traffic. But this prevents external checks from working, and may
break some very specific Lua scripts which actively rely on the ability to
fork. This option is there to disable this protection. Note that it is a bad
idea to disable it, as a vulnerability in a library or within HAProxy itself
will be easier to exploit once disabled. In addition, forking from Lua or
anywhere else is not reliable as the forked process may randomly embed a lock
set by another thread and never manage to finish an operation. As such it is
highly recommended that this option is never used and that any workload
requiring such a fork be reconsidered and moved to a safer solution (such as
agents instead of external checks). This option supports the "no" prefix to
disable it.
HAProxy doesn't need to call executables at run time (except when using
external checks which are strongly recommended against), and is even expected
to isolate itself into an empty chroot. As such, there basically is no valid
reason to allow a setuid executable to be called without the user being fully
aware of the risks. In a situation where HAProxy would need to call external
checks and/or disable chroot, exploiting a vulnerability in a library or in
HAProxy itself could lead to the execution of an external program. On Linux
it is possible to lock the process so that any setuid bit present on such an
executable is ignored. This significantly reduces the risk of privilege
escalation in such a situation. This is what HAProxy does by default. In case
this causes a problem to an external check (for example one which would need
the "ping" command), then it is possible to disable this protection by
explicitly adding this directive in the global section. If enabled, it is
possible to turn it back off by prefixing it with the "no" keyword.
Assigns a directory to load certificate chain for issuer completion. All
files must be in PEM format. For certificates loaded with "crt" or "crt-list",
if certificate chain is not included in PEM (also commonly known as
intermediate certificate), HAProxy will complete chain if the issuer of the
certificate corresponds to the first certificate of the chain loaded with
"issuers-chain-path".
A "crt" file with PrivateKey+Certificate+IntermediateCA2+IntermediateCA1
could be replaced with PrivateKey+Certificate. HAProxy will complete the
chain if a file with IntermediateCA2+IntermediateCA1 is present in
"issuers-chain-path" directory. All other certificates with the same issuer
will share the chain in memory.
This setting must be used to explicitly enable the QUIC listener bindings when
haproxy is compiled against a TLS/SSL stack without QUIC support, typically
OpenSSL. It has no effect when haproxy is compiled against a TLS/SSL stack
with QUIC support, quictls for instance. Note that QUIC 0-RTT is not supported
when this setting is set.
localpeer <name>
Sets the local instance's peer name. It will be ignored if the "-L"
command line argument is specified or if used after "peers" section
definitions. In such cases, a warning message will be emitted during
the configuration parsing.

This option will also set the HAPROXY_LOCALPEER environment variable.
See also "-L" in the management guide and "peers" section below.
log <target> [len <length>] [format <format>] [sample <ranges>:<sample_size>] <facility> [max level [min level]]
Adds a global syslog server. Several global servers can be defined. They
will receive logs for starts and exits, as well as all logs from proxies
configured with "log global". See "log" option for proxies for more details.
Sets the hostname field in the syslog header. If optional "string" parameter
is set the header is set to the string contents, otherwise uses the hostname
of the system. Generally used if one is not relaying logs through an
intermediate syslog server or for simply customizing the hostname printed in
the logs.
log-tag <string>
Sets the tag field in the syslog header to this string. It defaults to the
program name as launched from the command line, which usually is "haproxy".
Sometimes it can be useful to differentiate between multiple processes
running on the same host. See also the per-proxy "log-tag" directive.
lua-load <file> [ <arg1> [ <arg2> [ ... ] ] ]
This global directive loads and executes a Lua file in the shared context
that is visible to all threads. Any variable set in such a context is visible
from any thread. This is the easiest and recommended way to load Lua programs
but it will not scale well if a lot of Lua calls are performed, as only one
thread may be running on the global state at a time. A program loaded this
way will always see 0 in the "core.thread" variable. This directive can be
used multiple times.

args are available in the lua file using the code below in the body of the
file. Do not forget that Lua arrays start at index 1. A "local" variable
declared in a file is available in the entire file and not available on
other files.

   local args = table.pack(...)
lua-load-per-thread <file> [ <arg1> [ <arg2> [ ... ] ] ]
This global directive loads and executes a Lua file into each started thread.
Any global variable has a thread-local visibility so that each thread could
see a different value. As such it is strongly recommended not to use global
variables in programs loaded this way. An independent copy is loaded and
initialized for each thread, everything is done sequentially and in the
thread's numeric order from 1 to nbthread. If some operations need to be
performed only once, the program should check the "core.thread" variable to
figure what thread is being initialized. Programs loaded this way will run
concurrently on all threads and will be highly scalable. This is the
recommended way to load simple functions that register sample-fetches,
converters, actions or services once it is certain the program doesn't depend
on global variables. For the sake of simplicity, the directive is available
even if only one thread is used and even if threads are disabled (in which
case it will be equivalent to lua-load). This directive can be used multiple
times.

See lua-load for usage of args.
lua-prepend-path <string> [<type>]
Prepends the given string followed by a semicolon to Lua's package.<type>
variable.
<type> must either be "path" or "cpath". If <type> is not given it defaults
to "path".

Lua's paths are semicolon delimited lists of patterns that specify how the
`require` function attempts to find the source file of a library. Question
marks (?) within a pattern will be replaced by module name. The path is
evaluated left to right. This implies that paths that are prepended later
will be checked earlier.

As an example by specifying the following path:

  lua-prepend-path /usr/share/haproxy-lua/?/init.lua
  lua-prepend-path /usr/share/haproxy-lua/?.lua

When `require "example"` is being called Lua will first attempt to load the
/usr/share/haproxy-lua/example.lua script, if that does not exist the
/usr/share/haproxy-lua/example/init.lua will be attempted and the default
paths if that does not exist either.

See https://www.lua.org/pil/8.1.html for the details within the Lua
documentation.
master-worker [no-exit-on-failure]
Master-worker mode. It is equivalent to the command line "-W" argument.
This mode will launch a "master" which will monitor the "workers". Using
this mode, you can reload HAProxy directly by sending a SIGUSR2 signal to
the master. The master-worker mode is compatible either with the foreground
or daemon mode.

By default, if a worker exits with a bad return code, in the case of a
segfault for example, all workers will be killed, and the master will leave.
It is convenient to combine this behavior with Restart=on-failure in a
systemd unit file in order to relaunch the whole process. If you don't want
this behavior, you must use the keyword "no-exit-on-failure".

See also "-W" in the management guide.
In master-worker mode, this option limits the number of time a worker can
survive to a reload. If the worker did not leave after a reload, once its
number of reloads is greater than this number, the worker will receive a
SIGTERM. This option helps to keep under control the number of workers.
See also "show proc" in the Management Guide.
nbthread <number>
This setting is only available when support for threads was built in. It
makes HAProxy run on <number> threads. "nbthread" also works when HAProxy is
started in foreground. On some platforms supporting CPU affinity, the default
"nbthread" value is automatically set to the number of CPUs the process is
bound to upon startup. This means that the thread count can easily be
adjusted from the calling process using commands like "taskset" or "cpuset".
Otherwise, this value defaults to 1. The default value is reported in the
output of "haproxy -vv".
Disable QUIC transport protocol. All the QUIC listeners will still be created.
But they will not bind their addresses. Hence, no QUIC traffic will be
processed by haproxy. See also "quic_enabled" sample fetch.
If running on a NUMA-aware platform, HAProxy inspects on startup the CPU
topology of the machine. If a multi-socket machine is detected, the affinity
is automatically calculated to run on the CPUs of a single node. This is done
in order to not suffer from the performance penalties caused by the
inter-socket bus latency. However, if the applied binding is non optimal on a
particular architecture, it can be disabled with the statement 'no
numa-cpu-mapping'. This automatic binding is also not applied if a nbthread
statement is present in the configuration, or the affinity of the process is
already specified, for example via the 'cpu-map' directive or the taskset
utility.
pidfile <pidfile>
Writes PIDs of all daemons into file <pidfile> when daemon mode or writes PID
of master process into file <pidfile> when master-worker mode. This option is
equivalent to the "-p" command line argument. The file must be accessible to
the user starting the process. See also "daemon" and "master-worker".
A bug in the PROXY protocol v2 implementation was present in HAProxy up to
version 2.1, causing it to emit a PROXY command instead of a LOCAL command
for health checks. This is particularly minor but confuses some servers'
logs. Sadly, the bug was discovered very late and revealed that some servers
which possibly only tested their PROXY protocol implementation against
HAProxy fail to properly handle the LOCAL command, and permanently remain in
the "down" state when HAProxy checks them. When this happens, it is possible
to enable this global option to revert to the older (bogus) behavior for the
time it takes to contact the affected components' vendors and get them fixed.
This option is disabled by default and acts on all servers having the
"send-proxy-v2" statement.
presetenv <name> <value>
Sets environment variable <name> to value <value>. If the variable exists, it
is NOT overwritten. The changes immediately take effect so that the next line
in the configuration file sees the new value. See also "setenv", "resetenv",
and "unsetenv".
Performs a one-time open of the maximum file descriptor which results in a
pre-allocation of the kernel's data structures. This prevents short pauses
when nbthread>1 and HAProxy opens a file descriptor which requires the kernel
to expand its data structures.
resetenv [<name> ...]
Removes all environment variables except the ones specified in argument. It
allows to use a clean controlled environment before setting new values with
setenv or unsetenv. Please note that some internal functions may make use of
some environment variables, such as time manipulation functions, but also
OpenSSL or even external checks. This must be used with extreme care and only
after complete validation. The changes immediately take effect so that the
next line in the configuration file sees the new environment. See also
"setenv", "presetenv", and "unsetenv".
server-state-base <directory>
Specifies the directory prefix to be prepended in front of all servers state
file names which do not start with a '/'. See also "server-state-file",
"load-server-state-from-file" and "server-state-file-name".
Specifies the path to the file containing state of servers. If the path starts
with a slash ('/'), it is considered absolute, otherwise it is considered
relative to the directory specified using "server-state-base" (if set) or to
the current directory. Before reloading HAProxy, it is possible to save the
servers' current state using the stats command "show servers state". The
output of this command must be written in the file pointed by <file>. When
starting up, before handling traffic, HAProxy will read, load and apply state
for each server found in the file and available in its current running
configuration. See also "server-state-base" and "show servers state",
"load-server-state-from-file" and "server-state-file-name"
This option is better left disabled by default and enabled only upon a
developer's request. If it has been enabled, it may still be forcibly
disabled by prefixing it with the "no" keyword. It has no impact on
performance nor stability but will try hard to re-enable core dumps that were
possibly disabled by file size limitations (ulimit -f), core size limitations
(ulimit -c), or "dumpability" of a process after changing its UID/GID (such
as /proc/sys/fs/suid_dumpable on Linux). Core dumps might still be limited by
the current directory's permissions (check what directory the file is started
from), the chroot directory's permission (it may be needed to temporarily
disable the chroot directive or to move it to a dedicated writable location),
or any other system-specific constraint. For example, some Linux flavours are
notorious for replacing the default core file with a path to an executable
not even installed on the system (check /proc/sys/kernel/core_pattern). Often,
simply writing "core", "core.%p" or "/var/log/core/core.%p" addresses the
issue. When trying to enable this option waiting for a rare issue to
re-appear, it's often a good idea to first try to obtain such a dump by
issuing, for example, "kill -11" to the "haproxy" process and verify that it
leaves a core where expected when dying.
set-var <var-name> <expr>
Sets the process-wide variable '<var-name>' to the result of the evaluation
of the sample expression <expr>. The variable '<var-name>' may only be a
process-wide variable (using the 'proc.' prefix). It works exactly like the
'set-var' action in TCP or HTTP rules except that the expression is evaluated
at configuration parsing time and that the variable is instantly set. The
sample fetch functions and converters permitted in the expression are only
those using internal data, typically 'int(value)' or 'str(value)'. It is
possible to reference previously allocated variables as well. These variables
will then be readable (and modifiable) from the regular rule sets.
Example:
global
    set-var proc.current_state str(primary)
    set-var proc.prio int(100)
    set-var proc.threshold int(200),sub(proc.prio)
set-var-fmt <var-name> <fmt>
Sets the process-wide variable '<var-name>' to the string resulting from the
evaluation of the log-format <fmt>. The variable '<var-name>' may only be a
process-wide variable (using the 'proc.' prefix). It works exactly like the
'set-var-fmt' action in TCP or HTTP rules except that the expression is
evaluated at configuration parsing time and that the variable is instantly
set. The sample fetch functions and converters permitted in the expression
are only those using internal data, typically 'int(value)' or 'str(value)'.
It is possible to reference previously allocated variables as well. These
variables will then be readable (and modifiable) from the regular rule sets.
Please see section 8.2.4 for details on the log-format syntax.
Example:
global
    set-var-fmt proc.current_state "primary"
    set-var-fmt proc.bootid        "%pid|%t"
setcap <name>[,<name>...]
Sets a list of capabilities that must be preserved when starting with uid 0
and switching to a non-zero uid. By default all permissions are lost by the
uid switch, but some are often needed when trying connecting to a server from
a foreign address during transparent proxying, or when binding to a port
below 1024, e.g. when using "tune.quic.socket-owner connection", resulting in
setups running entirely under uid 0. Setting capabilities generally is a
safer alternative, as only the required capabilities will be preserved. The
feature is OS-specific and only enabled on Linux when USE_LINUX_CAP=1 is set
at build time. The list of supported capabilities also depends on the OS and
is enumerated by the error message displayed when an invalid capability name
or an empty one is passed. Multiple capabilities may be passed, delimited by
commas. Among those commonly used, "cap_net_raw" allows to transparently bind
to a foreign address, and "cap_net_bind_service" allows to bind to a
privileged port and may be used by QUIC.
setenv <name> <value>
Sets environment variable <name> to value <value>. If the variable exists, it
is overwritten. The changes immediately take effect so that the next line in
the configuration file sees the new value. See also "presetenv", "resetenv",
and "unsetenv".
This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of cipher algorithms ("cipher suite")
that are negotiated during the SSL/TLS handshake up to TLSv1.2 for all
"bind" lines which do not explicitly define theirs. The format of the string
is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/). For TLSv1.3
cipher configuration, please check the "ssl-default-bind-ciphersuites" keyword.
Please check the "bind" keyword for more information.
This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default string
describing the list of cipher algorithms ("cipher suite") that are negotiated
during the TLSv1.3 handshake for all "bind" lines which do not explicitly define
theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-bind-ciphers" keyword. Please check the "bind" keyword for more
information.
This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of signature algorithms related to
client authentication for all "bind" lines which do not explicitly define
theirs. The format of the string is a colon-delimited list of signature
algorithms. Each signature algorithm can use one of two forms: TLS1.3 signature
scheme names ("rsa_pss_rsae_sha256") or the public key algorithm + digest form
("ECDSA+SHA256"). A list can contain both forms. For more information on the
format, see SSL_CTX_set1_client_sigalgs(3). A list of signature algorithms is
also available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c
file.  This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.
This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of elliptic curves algorithms ("curve
suite") that are negotiated during the SSL/TLS handshake with ECDHE. The format
of the string is a colon-delimited list of curve name.
Please check the "bind" keyword for more information.
This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "bind" lines. Please check the "bind"
keyword to see available options.
Example:
global
   ssl-default-bind-options ssl-min-ver TLSv1.0 no-tls-tickets
This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of signature algorithms that
are negotiated during the TLSv1.2 and TLSv1.3 handshake for all "bind" lines
which do not explicitly define theirs. The format of the string is a
colon-delimited list of signature algorithms. Each signature algorithm can
use one of two forms: TLS1.3 signature scheme names ("rsa_pss_rsae_sha256")
or the public key algorithm + digest form ("ECDSA+SHA256"). A list
can contain both forms. For more information on the format,
see SSL_CTX_set1_sigalgs(3). A list of signature algorithms is also
available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c file.
This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.
This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of cipher algorithms that are
negotiated during the SSL/TLS handshake up to TLSv1.2 with the server,
for all "server" lines which do not explicitly define theirs. The format of
the string is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/).
For TLSv1.3 cipher configuration, please check the
"ssl-default-server-ciphersuites" keyword. Please check the "server" keyword
for more information.
This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default
string describing the list of cipher algorithms that are negotiated during
the TLSv1.3 handshake with the server, for all "server" lines which do not
explicitly define theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-server-ciphers" keyword. Please check the "server" keyword for
more information.
This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of signature algorithms related to
client authentication for all "server" lines which do not explicitly define
theirs. The format of the string is a colon-delimited list of signature
algorithms. Each signature algorithm can use one of two forms: TLS1.3 signature
scheme names ("rsa_pss_rsae_sha256") or the public key algorithm + digest form
("ECDSA+SHA256"). A list can contain both forms. For more information on the
format, see SSL_CTX_set1_client_sigalgs(3). A list of signature algorithms is
also available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c
file.  This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.
This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of elliptic curves algorithms ("curve
suite") that are negotiated during the SSL/TLS handshake with ECDHE. The format
of the string is a colon-delimited list of curve name.
Please check the "server" keyword for more information.
This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "server" lines. Please check the "server"
keyword to see available options.
This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of signature algorithms that
are negotiated during the TLSv1.2 and TLSv1.3 handshake for all "server" lines
which do not explicitly define theirs. The format of the string is a
colon-delimited list of signature algorithms. Each signature algorithm can
use one of two forms: TLS1.3 signature scheme names ("rsa_pss_rsae_sha256")
or the public key algorithm + digest form ("ECDSA+SHA256"). A list
can contain both forms. For more information on the format,
see SSL_CTX_set1_sigalgs(3). A list of signature algorithms is also
available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c file.
This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.
This setting is only available when support for OpenSSL was built in. It sets
the default DH parameters that are used during the SSL/TLS handshake when
ephemeral Diffie-Hellman (DHE) key exchange is used, for all "bind" lines
which do not explicitly define theirs. It will be overridden by custom DH
parameters found in a bind certificate file if any. If custom DH parameters
are not specified either by using ssl-dh-param-file or by setting them
directly in the certificate file, DHE ciphers will not be used, unless
tune.ssl.default-dh-param is set. In this latter case, pre-defined DH
parameters of the specified size will be used. Custom parameters are known to
be more secure and therefore their use is recommended.
Custom DH parameters may be generated by using the OpenSSL command
"openssl dhparam <size>", where size should be at least 2048, as 1024-bit DH
parameters should not be considered secure anymore.
This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to define a default property
string used when fetching algorithms in providers. It behave the same way as
the openssl propquery option and it follows the same syntax (described in
https://www.openssl.org/docs/man3.0/man7/property.html). For instance, if you
have two providers loaded, the foo one and the default one, the propquery
"?provider=foo" allows to pick the algorithm implementations provided by the
foo provider by default, and to fallback on the default provider's one if it
was not found.
This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to load a provider during init.
If loading is successful, any capabilities provided by the loaded provider
might be used by HAProxy. Multiple 'ssl-provider' options can be specified in
a configuration file. The providers will be loaded in their order of
appearance.

Please note that loading a provider explicitly prevents OpenSSL from loading
the 'default' provider automatically. OpenSSL also allows to define the
providers that should be loaded directly in its configuration file
(openssl.cnf for instance) so it is not necessary to use this 'ssl-provider'
option to load providers. The "show ssl providers" CLI command can be used to
show all the providers that were successfully loaded.

The default search path of OpenSSL provider can be found in the output of the
"openssl version -a" command. If the provider is in another directory, you
can set the OPENSSL_MODULES environment variable, which takes the directory
where your provider can be found.

See also "ssl-propquery" and "ssl-provider-path".
This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to specify the search path that
is to be used by OpenSSL for looking for providers. It behaves the same way
as the OPENSSL_MODULES environment variable. It will be used for any
following 'ssl-provider' option or until a new 'ssl-provider-path' is
defined.
See also "ssl-provider".
This setting allows to configure the way HAProxy does the lookup for the
extra SSL files. By default HAProxy adds a new extension to the filename.
(ex: with "foobar.crt" load "foobar.crt.key"). With this option enabled,
HAProxy removes the extension before adding the new one (ex: with
"foobar.crt" load "foobar.key").

Your crt file must have a ".crt" extension for this option to work.

This option is not compatible with bundle extensions (.ecdsa, .rsa. .dsa)
and won't try to remove them.

This option is disabled by default. See also "ssl-load-extra-files".
ssl-load-extra-files <none|all|bundle|sctl|ocsp|issuer|key>*
This setting alters the way HAProxy will look for unspecified files during
the loading of the SSL certificates. This option applies to certificates
associated to "bind" lines as well as "server" lines but some of the extra
files will not have any functional impact for "server" line certificates.

By default, HAProxy discovers automatically a lot of files not specified in
the configuration, and you may want to disable this behavior if you want to
optimize the startup time.

"none": Only load the files specified in the configuration. Don't try to load
a certificate bundle if the file does not exist. In the case of a directory,
it won't try to bundle the certificates if they have the same basename.

"all": This is the default behavior, it will try to load everything,
bundles, sctl, ocsp, issuer, key.

"bundle": When a file specified in the configuration does not exist, HAProxy
will try to load a "cert bundle". Certificate bundles are only managed on the
frontend side and will not work for backend certificates.

Starting from HAProxy 2.3, the bundles are not loaded in the same OpenSSL
certificate store, instead it will loads each certificate in a separate
store which is equivalent to declaring multiple "crt". OpenSSL 1.1.1 is
required to achieve this. Which means that bundles are now used only for
backward compatibility and are not mandatory anymore to do an hybrid RSA/ECC
bind configuration.

To associate these PEM files into a "cert bundle" that is recognized by
HAProxy, they must be named in the following way: All PEM files that are to
be bundled must have the same base name, with a suffix indicating the key
type. Currently, three suffixes are supported: rsa, dsa and ecdsa. For
example, if www.example.com has two PEM files, an RSA file and an ECDSA
file, they must be named: "example.pem.rsa" and "example.pem.ecdsa". The
first part of the filename is arbitrary; only the suffix matters. To load
this bundle into HAProxy, specify the base name only:
Example :
bind :8443 ssl crt example.pem
Note that the suffix is not given to HAProxy; this tells HAProxy to look for
a cert bundle.

HAProxy will load all PEM files in the bundle as if they were configured
separately in several "crt".

The bundle loading does not have an impact anymore on the directory loading
since files are loading separately.

On the CLI, bundles are seen as separate files, and the bundle extension is
required to commit them.

OCSP files (.ocsp), issuer files (.issuer), Certificate Transparency (.sctl)
as well as private keys (.key) are supported with multi-cert bundling.

"sctl": Try to load "<basename>.sctl" for each crt keyword. If provided for
a backend certificate, it will be loaded but will not have any functional
impact.

"ocsp": Try to load "<basename>.ocsp" for each crt keyword. If provided for
a backend certificate, it will be loaded but will not have any functional
impact.

"issuer": Try to load "<basename>.issuer" if the issuer of the OCSP file is
not provided in the PEM file. If provided for a backend certificate, it will
be loaded but will not have any functional impact.

"key": If the private key was not provided by the PEM file, try to load a
file "<basename>.key" containing a private key.

The default behavior is "all".
Example:
ssl-load-extra-files bundle sctl
ssl-load-extra-files sctl ocsp issuer
ssl-load-extra-files none
ssl-server-verify [none|required]
The default behavior for SSL verify on servers side. If specified to 'none',
servers certificates are not verified. The default is 'required' except if
forced using cmdline option '-dV'.
Self issued CA, aka x509 root CA, is the anchor for chain validation: as a
server is useless to send it, client must have it. Standard configuration
need to not include such CA in PEM file. This option allows you to keep such
CA in PEM file without sending it to the client. Use case is to provide
issuer for ocsp without the need for '.issuer' file and be able to share it
with 'issuers-chain-path'. This concerns all certificates without intermediate
certificates. It's useless for BoringSSL, .issuer is ignored because ocsp
bits does not need it. Requires at least OpenSSL 1.0.2.
stats maxconn <connections>
By default, the stats socket is limited to 10 concurrent connections. It is
possible to change this value with "stats maxconn".
stats socket [<address:port>|<path>] [param*]
Binds a UNIX socket to <path> or a TCPv4/v6 address to <address:port>.
Connections to this socket will return various statistics outputs and even
allow some commands to be issued to change some runtime settings. Please
consult section 9.3 "Unix Socket commands" of Management Guide for more
details.

All parameters supported by "bind" lines are supported, for instance to
restrict access to some users or their access rights. Please consult
section 5.1 for more information.
stats timeout <timeout, in milliseconds>
The default timeout on the stats socket is set to 10 seconds. It is possible
to change this value with "stats timeout". The value must be passed in
milliseconds, or be suffixed by a time unit among { us, ms, s, m, h, d }.
Makes process fail at startup when a setrlimit fails. HAProxy tries to set the
best setrlimit according to what has been calculated. If it fails, it will
emit a warning. This option is here to guarantee an explicit failure of
HAProxy when those limits fail. It is enabled by default. It may still be
forcibly disabled by prefixing it with the "no" keyword.
thread-group <group> [<thread-range>...]
This setting is only available when support for threads was built in. It
enumerates the list of threads that will compose thread group <group>.
Thread numbers and group numbers start at 1. Thread ranges are defined either
using a single thread number at once, or by specifying the lower and upper
bounds delimited by a dash '-' (e.g. "1-16"). Unassigned threads will be
automatically assigned to unassigned thread groups, and thread groups
defined with this directive will never receive more threads than those
defined. Defining the same group multiple times overrides previous
definitions with the new one. See also "nbthread" and "thread-groups".
thread-groups <number>
This setting is only available when support for threads was built in. It
makes HAProxy split its threads into <number> independent groups. At the
moment, the default value is 1. Thread groups make it possible to reduce
sharing between threads to limit contention, at the expense of some extra
configuration efforts. It is also the only way to use more than 64 threads
since up to 64 threads per group may be configured. The maximum number of
groups is configured at compile time and defaults to 16. See also "nbthread".
trace <args...>
This command configures one "trace" subsystem statement. Each of them can be
found in the management manual, and follow the exact same syntax. Only one
statement per line is permitted (i.e. if some long trace configurations using
semi-colons are to be imported, they must be placed one per line). Any output
that the "trace" command would produce will be emitted during the parsing
step of the section. Most of the time these will be errors and warnings, but
certain incomplete commands might list permissible choices. This command is
not meant for regular use, it will generally only be suggested by developers
along complex debugging sessions. For this reason it is internally marked as
experimental, meaning that "expose-experimental-directives" must appear on a
line before any "trace" statement. Note that these directives are parsed on
the fly, so referencing a ring buffer that is only declared further will not
work. For such use cases it is suggested to place another "global" section
with only the "trace" statements after the declaration of that ring. It is
important to keep in mind that depending on the trace level and details,
enabling traces can severely degrade the global performance. Please refer to
the management manual for the statements syntax.
uid <number>
Changes the process's user ID to <number>. It is recommended that the user ID
is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with superuser privileges in order to be able to switch to another
one. See also "gid" and "user".
ulimit-n <number>
Sets the maximum number of per-process file-descriptors to <number>. By
default, it is automatically computed, so it is recommended not to use this
option. If the intent is only to limit the number of file descriptors, better
use "fd-hard-limit" instead.

Note that the dynamic servers are not taken into account in this automatic
resource calculation. If using a large number of them, it may be needed to
manually specify this value.
unix-bind [ prefix <prefix> ] [ mode <mode> ] [ user <user> ] [ uid <uid> ] [ group <group> ] [ gid <gid> ]
Fixes common settings to UNIX listening sockets declared in "bind" statements.
This is mainly used to simplify declaration of those UNIX sockets and reduce
the risk of errors, since those settings are most commonly required but are
also process-specific. The <prefix> setting can be used to force all socket
path to be relative to that directory. This might be needed to access another
component's chroot. Note that those paths are resolved before HAProxy chroots
itself, so they are absolute. The <mode>, <user>, <uid>, <group> and <gid>
all have the same meaning as their homonyms used by the "bind" statement. If
both are specified, the "bind" statement has priority, meaning that the
"unix-bind" settings may be seen as process-wide default settings.
unsetenv [<name> ...]
Removes environment variables specified in arguments. This can be useful to
hide some sensitive information that are occasionally inherited from the
user's environment during some operations. Variables which did not exist are
silently ignored so that after the operation, it is certain that none of
these variables remain. The changes immediately take effect so that the next
line in the configuration file will not see these variables. See also
"setenv", "presetenv", and "resetenv".
user <user name>
Similar to "uid" but uses the UID of user name <user name> from /etc/passwd.
See also "uid" and "group".
node <name>
Only letters, digits, hyphen and underscore are allowed, like in DNS names.

This statement is useful in HA configurations where two or more processes or
servers share the same IP address. By setting a different node-name on all
nodes, it becomes easy to immediately spot what server is handling the
traffic.
Sets the WURFL Useragent cache size. For faster lookups, already processed user
agents are kept in a LRU cache :
- "0"     : no cache is used.
- <size>  : size of lru cache in elements.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.
wurfl-data-file <file path>
The path of the WURFL data file to provide device detection services. The
file should be accessible by HAProxy with relevant permissions.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.
wurfl-information-list [<capability>]*
A space-delimited list of WURFL capabilities, virtual capabilities, property
names we plan to use in injected headers. A full list of capability and
virtual capability names is available on the Scientiamobile website :

    https://www.scientiamobile.com/wurflCapability

Valid WURFL properties are:
- wurfl_id                    Contains the device ID of the matched device.

- wurfl_root_id               Contains the device root ID of the matched
                              device.

- wurfl_isdevroot             Tells if the matched device is a root device.
                              Possible values are "TRUE" or "FALSE".

- wurfl_useragent             The original useragent coming with this
                              particular web request.

- wurfl_api_version           Contains a string representing the currently
                              used Libwurfl API version.

- wurfl_info                  A string containing information on the parsed
                              wurfl.xml and its full path.

- wurfl_last_load_time        Contains the UNIX timestamp of the last time
                              WURFL has been loaded successfully.

- wurfl_normalized_useragent  The normalized useragent.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.
A char that will be used to separate values in a response header containing
WURFL results. If not set that a comma (',') will be used by default.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.
wurfl-patch-file [<file path>]
A list of WURFL patch file paths. Note that patches are loaded during startup
thus before the chroot.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

3.2. Performance tuning

In some situations, especially when dealing with low latency on processors
supporting a variable frequency or when running inside virtual machines, each
time the process waits for an I/O using the poller, the processor goes back
to sleep or is offered to another VM for a long time, and it causes
excessively high latencies. This option provides a solution preventing the
processor from sleeping by always using a null timeout on the pollers. This
results in a significant latency reduction (30 to 100 microseconds observed)
at the expense of a risk to overheat the processor. It may even be used with
threads, in which case improperly bound threads may heavily conflict,
resulting in a worse performance and high values for the CPU stolen fields
in "show info" output, indicating which threads are misconfigured. It is
important not to let the process run on the same processor as the network
interrupts when this option is used. It is also better to avoid using it on
multiple CPU threads sharing the same core. This option is disabled by
default. If it has been enabled, it may still be forcibly disabled by
prefixing it with the "no" keyword. It is ignored by the "select" and
"poll" pollers.

This option is automatically disabled on old processes in the context of
seamless reload; it avoids too much cpu conflicts when multiple processes
stay around for some time waiting for the end of their current connections.
max-spread-checks <delay in milliseconds>
By default, HAProxy tries to spread the start of health checks across the
smallest health check interval of all the servers in a farm. The principle is
to avoid hammering services running on the same server. But when using large
check intervals (10 seconds or more), the last servers in the farm take some
time before starting to be tested, which can be a problem. This parameter is
used to enforce an upper bound on delay between the first and the last check,
even if the servers' check intervals are larger. When servers run with
shorter intervals, their intervals will be respected though.
Sets the maximum CPU usage HAProxy can reach before stopping the compression
for new requests or decreasing the compression level of current requests.
It works like 'maxcomprate' but measures CPU usage instead of incoming data
bandwidth. The value is expressed in percent of the CPU used by HAProxy. A
value of 100 disable the limit. The default value is 100. Setting a lower
value will prevent the compression work from slowing the whole process down
and from introducing high latencies.
maxcomprate <number>
Sets the maximum per-process input compression rate to <number> kilobytes
per second. For each stream, if the maximum is reached, the compression
level will be decreased during the stream. If the maximum is reached at the
beginning of a stream, the stream will not compress at all. If the maximum
is not reached, the compression level will be increased up to
tune.comp.maxlevel. A value of zero means there is no limit, this is the
default value.
maxconn <number>
Sets the maximum per-process number of concurrent connections to <number>. It
is equivalent to the command-line argument "-n". Proxies will stop accepting
connections when this limit is reached. The "ulimit-n" parameter is
automatically adjusted according to this value. See also "ulimit-n". Note:
the "select" poller cannot reliably use more than 1024 file descriptors on
some platforms. If your platform only supports select and reports "select
FAILED" on startup, you need to reduce maxconn until it works (slightly
below 500 in general). If this value is not set, it will automatically be
calculated based on the current file descriptors limit reported by the
"ulimit -n" command, possibly reduced to a lower value if a memory limit
is enforced, based on the buffer size, memory allocated to compression, SSL
cache size, and use or not of SSL and the associated maxsslconn (which can
also be automatic). In any case, the fd-hard-limit applies if set.
maxconnrate <number>
Sets the maximum per-process number of connections per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.
maxpipes <number>
Sets the maximum per-process number of pipes to <number>. Currently, pipes
are only used by kernel-based tcp splicing. Since a pipe contains two file
descriptors, the "ulimit-n" value will be increased accordingly. The default
value is maxconn/4, which seems to be more than enough for most heavy usages.
The splice code dynamically allocates and releases pipes, and can fall back
to standard copy, so setting this value too low may only impact performance.
maxsessrate <number>
Sets the maximum per-process number of sessions per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.
maxsslconn <number>
Sets the maximum per-process number of concurrent SSL connections to
<number>. By default there is no SSL-specific limit, which means that the
global maxconn setting will apply to all connections. Setting this limit
avoids having openssl use too much memory and crash when malloc returns NULL
(since it unfortunately does not reliably check for such conditions). Note
that the limit applies both to incoming and outgoing connections, so one
connection which is deciphered then ciphered accounts for 2 SSL connections.
If this value is not set, but a memory limit is enforced, this value will be
automatically computed based on the memory limit, maxconn,  the buffer size,
memory allocated to compression, SSL cache size, and use of SSL in either
frontends, backends or both. If neither maxconn nor maxsslconn are specified
when there is a memory limit, HAProxy will automatically adjust these values
so that 100% of the connections can be made over SSL with no risk, and will
consider the sides where it is enabled (frontend, backend, both).
maxsslrate <number>
Sets the maximum per-process number of SSL sessions per second to <number>.
SSL listeners will stop accepting connections when this limit is reached. It
can be used to limit the global SSL CPU usage regardless of each frontend
capacity. It is important to note that this can only be used as a service
protection measure, as there will not necessarily be a fair share between
frontends when the limit is reached, so it's a good idea to also limit each
frontend to some value close to its expected share. It is also important to
note that the sessions are accounted before they enter the SSL stack and not
after, which also protects the stack against bad handshakes. Also, lowering
tune.maxaccept can improve fairness.
maxzlibmem <number>
Sets the maximum amount of RAM in megabytes per process usable by the zlib.
When the maximum amount is reached, future streams will not compress as long
as RAM is unavailable. When sets to 0, there is no limit.
The default value is 0. The value is available in bytes on the UNIX socket
with "show info" on the line "MaxZlibMemUsage", the memory used by zlib is
"ZlibMemUsage" in bytes.
Disables memory trimming ("malloc_trim") at a few moments where attempts are
made to reclaim lots of memory (on memory shortage or on reload). Trimming
memory forces the system's allocator to scan all unused areas and to release
them. This is generally seen as nice action to leave more available memory to
a new process while the old one is unlikely to make significant use of it.
But some systems dealing with tens to hundreds of thousands of concurrent
connections may experience a lot of memory fragmentation, that may render
this release operation extremely long. During this time, no more traffic
passes through the process, new connections are not accepted anymore, some
health checks may even fail, and the watchdog may even trigger and kill the
unresponsive process, leaving a huge core dump. If this ever happens, then it
is suggested to use this option to disable trimming and stop trying to be
nice with the new process. Note that advanced memory allocators usually do
not suffer from such a problem.
Disables the use of the "epoll" event polling system on Linux. It is
equivalent to the command-line argument "-de". The next polling system
used will generally be "poll". See also "nopoll".
Disables the use of the event ports event polling system on SunOS systems
derived from Solaris 10 and later. It is equivalent to the command-line
argument "-dv". The next polling system used will generally be "poll". See
also "nopoll".
Disables the use of getaddrinfo(3) for name resolving. It is equivalent to
the command line argument "-dG". Deprecated gethostbyname(3) will be used.
Disables the use of the "kqueue" event polling system on BSD. It is
equivalent to the command-line argument "-dk". The next polling system
used will generally be "poll". See also "nopoll".
Disables the use of the "poll" event polling system. It is equivalent to the
command-line argument "-dp". The next polling system used will be "select".
It should never be needed to disable "poll" since it's available on all
platforms supported by HAProxy. See also "nokqueue", "noepoll" and
"noevports".
Disables the use of SO_REUSEPORT - see socket(7). It is equivalent to the
command line argument "-dR".
Disables the use of kernel tcp splicing between sockets on Linux. It is
equivalent to the command line argument "-dS". Data will then be copied
using conventional and more portable recv/send calls. Kernel tcp splicing is
limited to some very recent instances of kernel 2.6. Most versions between
2.6.25 and 2.6.28 are buggy and will forward corrupted data, so they must not
be used. This option makes it easier to globally disable kernel splicing in
case of doubt. See also "option splice-auto", "option splice-request" and
"option splice-response".
profiling.memory { on | off }
Enables ('on') or disables ('off') per-function memory profiling. This will
keep usage statistics of malloc/calloc/realloc/free calls anywhere in the
process (including libraries) which will be reported on the CLI using the
"show profiling" command. This is essentially meant to be used when an
abnormal memory usage is observed that cannot be explained by the pools and
other info are required. The performance hit will typically be around 1%,
maybe a bit more on highly threaded machines, so it is normally suitable for
use in production. The same may be achieved at run time on the CLI using the
"set profiling memory" command, please consult the management manual.
profiling.tasks { auto | on | off }
Enables ('on') or disables ('off') per-task CPU profiling. When set to 'auto'
the profiling automatically turns on a thread when it starts to suffer from
an average latency of 1000 microseconds or higher as reported in the
"avg_loop_us" activity field, and automatically turns off when the latency
returns below 990 microseconds (this value is an average over the last 1024
loops so it does not vary quickly and tends to significantly smooth short
spikes). It may also spontaneously trigger from time to time on overloaded
systems, containers, or virtual machines, or when the system swaps (which
must absolutely never happen on a load balancer).

CPU profiling per task can be very convenient to report where the time is
spent and which requests have what effect on which other request. Enabling
it will typically affect the overall's performance by less than 1%, thus it
is recommended to leave it to the default 'auto' value so that it only
operates when a problem is identified. This feature requires a system
supporting the clock_gettime(2) syscall with clock identifiers
CLOCK_MONOTONIC and CLOCK_THREAD_CPUTIME_ID, otherwise the reported time will
be zero. This option may be changed at run time using "set profiling" on the
CLI.
spread-checks <0..50, in percent>
Sometimes it is desirable to avoid sending agent and health checks to
servers at exact intervals, for instance when many logical servers are
located on the same physical server. With the help of this parameter, it
becomes possible to add some randomness in the check interval between 0
and +/- 50%. A value between 2 and 5 seems to show good results. The
default value remains at 0.
ssl-engine <name> [algo <comma-separated list of algorithms>]
Sets the OpenSSL engine to <name>. List of valid values for <name> may be
obtained using the command "openssl engine". This statement may be used
multiple times, it will simply enable multiple crypto engines. Referencing an
unsupported engine will prevent HAProxy from starting. Note that many engines
will lead to lower HTTPS performance than pure software with recent
processors. The optional command "algo" sets the default algorithms an ENGINE
will supply using the OPENSSL function ENGINE_set_default_string(). A value
of "ALL" uses the engine for all cryptographic operations. If no list of
algo is specified then the value of "ALL" is used. A comma-separated list
of different algorithms may be specified, including: RSA, DSA, DH, EC, RAND,
CIPHERS, DIGESTS, PKEY, PKEY_CRYPTO, PKEY_ASN1. This is the same format that
openssl configuration file uses:
https://www.openssl.org/docs/man1.0.2/apps/config.html

HAProxy Version 2.6 disabled the support for engines in the default build.
This option is only available when HAProxy has been built with support for
it.  In case the ssl-engine is required HAProxy can be rebuild with the
USE_ENGINE=1 flag.
Adds SSL_MODE_ASYNC mode to the SSL context. This enables asynchronous TLS
I/O operations if asynchronous capable SSL engines are used. The current
implementation supports a maximum of 32 engines. The Openssl ASYNC API
doesn't support moving read/write buffers and is not compliant with
HAProxy's buffer management. So the asynchronous mode is disabled on
read/write  operations (it is only enabled during initial and renegotiation
handshakes).
Enables ('on') of disabled ('off') the zero-copy forwarding of data for the
applets. It is enabled by default.
Sets a hard limit on the number of buffers which may be allocated per process.
The default value is zero which means unlimited. The minimum non-zero value
will always be greater than "tune.buffers.reserve" and should ideally always
be about twice as large. Forcing this value can be particularly useful to
limit the amount of memory a process may take, while retaining a sane
behavior. When this limit is reached, streams which need a buffer wait for
another one to be released by another stream. Since buffers are dynamically
allocated and released, the waiting time is very short and not perceptible
provided that limits remain reasonable. In fact sometimes reducing the limit
may even increase performance by increasing the CPU cache's efficiency. Tests
have shown good results on average HTTP traffic with a limit to 1/10 of the
expected global maxconn setting, which also significantly reduces memory
usage. The memory savings come from the fact that a number of connections
will not allocate 2*tune.bufsize. It is best not to touch this value unless
advised to do so by an HAProxy core developer.
Sets the number of buffers which are pre-allocated and reserved for use only
during memory shortage conditions resulting in failed memory allocations. The
minimum value is 2 and is also the default. There is no reason a user would
want to change this value, it's mostly aimed at HAProxy core developers.
tune.bufsize <number>
Sets the buffer size to this size (in bytes). Lower values allow more
streams to coexist in the same amount of RAM, and higher values allow some
applications with very large cookies to work. The default value is 16384 and
can be changed at build time. It is strongly recommended not to change this
from the default value, as very low values will break some services such as
statistics, and values larger than default size will increase memory usage,
possibly causing the system to run out of memory. At least the global maxconn
parameter should be decreased by the same factor as this one is increased. In
addition, use of HTTP/2 mandates that this value must be 16384 or more. If an
HTTP request is larger than (tune.bufsize - tune.maxrewrite), HAProxy will
return HTTP 400 (Bad Request) error. Similarly if an HTTP response is larger
than this size, HAProxy will return HTTP 502 (Bad Gateway). Note that the
value set using this parameter will automatically be rounded up to the next
multiple of 8 on 32-bit machines and 16 on 64-bit machines.
Sets the maximum compression level. The compression level affects CPU
usage during compression. This value affects CPU usage during compression.
Each stream using compression initializes the compression algorithm with
this value. The default value is 1.
tune.disable-fast-forward [ EXPERIMENTAL ]
Disables the data fast-forwarding. It is a mechanism to optimize the data
forwarding by passing data directly from a side to the other one without
waking the stream up. Thanks to this directive, it is possible to disable
this optimization. Note it also disable any kernel tcp splicing but also the
zero-copy forwarding. This command is not meant for regular use, it will
generally only be suggested by developers along complex debugging
sessions. For this reason it is internally marked as experimental, meaning
that "expose-experimental-directives" must appear on a line before this
directive.
Globally disables the zero-copy forwarding of data. It is a mechanism to
optimize the data fast-forwarding by avoiding to use the channel's buffer.
Thanks to this directive, it is possible to disable this optimization. Note
it also disable any kernel tcp splicing.
Sets the number of events that may be processed at once by an asynchronous
task handler (from event_hdl API). <number> should be included between 1
and 10000. Large number could cause thread contention as a result of the
task doing heavy work without interruption, and on the other hand, small
number could result in the task being constantly rescheduled because it
cannot consume enough events per run and is not able to catch up with the
event producer. The default value may be forced at build time, otherwise
defaults to 100.
If compiled with DEBUG_FAIL_ALLOC or started with "-dMfail", gives the
percentage of chances an allocation attempt fails. Must be between 0 (no
failure) and 100 (no success). This is useful to debug and make sure memory
failures are handled gracefully. When not set, the ratio is 0. However the
command-line "-dMfail" option automatically sets it to 1% failure rate so that
it is not necessary to change the configuration for testing.
tune.fd.edge-triggered { on | off } [ EXPERIMENTAL ]
Enables ('on') or disables ('off') the edge-triggered polling mode for FDs
that support it. This is currently only support with epoll. It may noticeably
reduce the number of epoll_ctl() calls and slightly improve performance in
certain scenarios. This is still experimental, it may result in frozen
connections if bugs are still present, and is disabled by default.
Enables ('on') of disabled ('off') the zero-copy receives of data for the H1
multiplexer. It is enabled by default.
Enables ('on') of disabled ('off') the zero-copy sends of data for the H1
multiplexer. It is enabled by default.
Sets the HTTP/2 initial window size for outgoing connections, which is the
number of bytes the server can respond before waiting for an acknowledgment
from HAProxy. This setting only affects payload contents, not headers. When
not set, the common default value set by tune.h2.initial-window-size applies.
It can make sense to slightly increase this value to allow faster downloads
or to reduce CPU usage on the servers, at the expense of creating unfairness
between clients. It doesn't affect resource usage.
Sets the HTTP/2 maximum number of concurrent streams per outgoing connection
(i.e. the number of outstanding requests on a single connection to a server).
When not set, the default set by tune.h2.max-concurrent-streams applies. A
smaller value than the default 100 may improve a site's responsiveness at the
expense of maintaining more established connections to the servers. When the
"http-reuse" setting is set to "always", it is recommended to reduce this
value so as not to mix too many different clients over the same connection,
because if a client is slower than others, a mechanism known as "head of
line blocking" tends to cause cascade effect on download speed for all
clients sharing a connection (keep tune.h2.be.initial-window-size low in this
case). It is highly recommended not to increase this value; some might find
it optimal to run at low values (1..5 typically).
Sets the HTTP/2 initial window size for incoming connections, which is the
number of bytes the client can upload before waiting for an acknowledgment
from HAProxy. This setting only affects payload contents (i.e. the body of
POST requests), not headers. When not set, the common default value set by
tune.h2.initial-window-size applies. It can make sense to increase this value
to allow faster uploads. The default value of 65536 allows up to 5 Mbps of
bandwidth per client over a 100 ms ping time, and 500 Mbps for 1 ms ping
time. It doesn't affect resource usage. Using too large values may cause
clients to experience a lack of responsiveness if pages are accessed in
parallel to large uploads.
Sets the HTTP/2 maximum number of concurrent streams per incoming connection
(i.e. the number of outstanding requests on a single connection from a
client). When not set, the default set by tune.h2.max-concurrent-streams
applies. A larger value than the default 100 may sometimes slightly improve
the page load time for complex sites with lots of small objects over high
latency networks but can also result in using more memory by allowing a
client to allocate more resources at once. The default value of 100 is
generally good and it is recommended not to change this value.
Sets the HTTP/2 maximum number of total streams processed per incoming
connection. Once this limit is reached, HAProxy will send a graceful GOAWAY
frame informing the client that it will close the connection after all
pending streams have been closed. In practice, clients tend to close as fast
as possible when receiving this, and to establish a new connection for next
requests. Doing this is sometimes useful and desired in situations where
clients stay connected for a very long time and cause some imbalance inside a
farm. For example, in some highly dynamic environments, it is possible that
new load balancers are instantiated on the fly to adapt to a load increase,
and that once the load goes down they should be stopped without breaking
established connections. By setting a limit here, the connections will have
a limited lifetime and will be frequently renewed, with some possibly being
established to other nodes, so that existing resources are quickly released.

It's important to understand that there is an implicit relation between this
limit and "tune.h2.fe.max-concurrent-streams" above. Indeed, HAProxy will
always accept to process any possibly pending streams that might be in flight
between the client and the frontend, so the advertised limit will always
automatically be raised by the value configured in max-concurrent-streams,
and this value will serve as a hard limit above which a violation by a non-
compliant client will result in the connection being closed. Thus when
counting the number of requests per connection from the logs, any number
between max-total-streams and (max-total-streams + max-concurrent-streams)
may be observed depending on how fast streams are created by the client.

The default value is zero, which enforces no limit beyond those implied by
the protocol (2^30 ~= 1.07 billion). Values around 1000 may already cause
frequent connection renewal without causing any perceptible latency to most
clients. Setting it too low may result in an increase of CPU usage due to
frequent TLS reconnections, in addition to increased page load time. Please
note that some load testing tools do not support reconnections and may report
errors with this setting; as such it may be needed to disable it when running
performance benchmarks. See also "tune.h2.fe.max-concurrent-streams".
Sets the HTTP/2 dynamic header table size. It defaults to 4096 bytes and
cannot be larger than 65536 bytes. A larger value may help certain clients
send more compact requests, depending on their capabilities. This amount of
memory is consumed for each HTTP/2 connection. It is recommended not to
change it.
Sets the default value for the HTTP/2 initial window size, on both incoming
and outgoing connections. This value is used for incoming connections when
tune.h2.fe.initial-window-size is not set, and by outgoing connections when
tune.h2.be.initial-window-size is not set. The default value is 65536, which
for uploads roughly allows up to 5 Mbps of bandwidth per client over a
network showing a 100 ms ping time, or 500 Mbps over a 1-ms local network.
Given that changing the default value will both increase upload speeds and
cause more unfairness between clients on downloads, it is recommended to
instead use the side-specific settings tune.h2.fe.initial-window-size and
tune.h2.be.initial-window-size.
Sets the default HTTP/2 maximum number of concurrent streams per connection
(i.e. the number of outstanding requests on a single connection). This value
is used for incoming connections when tune.h2.fe.max-concurrent-streams is
not set, and for outgoing connections when tune.h2.be.max-concurrent-streams
is not set. The default value is 100. The impact varies depending on the side
so please see the two settings above for more details. It is recommended not
to use this setting and to switch to the per-side ones instead. A value of
zero disables the limit so a single client may create as many streams as
allocatable by HAProxy. It is highly recommended not to change this value.
Sets the HTTP/2 maximum frame size that HAProxy announces it is willing to
receive to its peers. The default value is the largest between 16384 and the
buffer size (tune.bufsize). In any case, HAProxy will not announce support
for frame sizes larger than buffers. The main purpose of this setting is to
allow to limit the maximum frame size setting when using large buffers. Too
large frame sizes might have performance impact or cause some peers to
misbehave. It is highly recommended not to change this value.
Enables ('on') of disabled ('off') the zero-copy sends of data for the H2
multiplexer. It is enabled by default.
Sets the maximum length of captured cookies. This is the maximum value that
the "capture cookie xxx len yyy" will be allowed to take, and any upper value
will automatically be truncated to this one. It is important not to set too
high a value because all cookie captures still allocate this size whatever
their configured value (they share a same pool). This value is per request
per response, so the memory allocated is twice this value per connection.
When not specified, the limit is set to 63 characters. It is recommended not
to change this value.
Sets the maximum length of request URI in logs. This prevents truncating long
request URIs with valuable query strings in log lines. This is not related
to syslog limits. If you increase this limit, you may also increase the
'log ... len yyy' parameter. Your syslog daemon may also need specific
configuration directives too.
The default value is 1024.
Sets the maximum number of headers in a request. When a request comes with a
number of headers greater than this value (including the first line), it is
rejected with a "400 Bad Request" status code. Similarly, too large responses
are blocked with "502 Bad Gateway". The default value is 101, which is enough
for all usages, considering that the widely deployed Apache server uses the
same limit. It can be useful to push this limit further to temporarily allow
a buggy application to work by the time it gets fixed. The accepted range is
1..32767. Keep in mind that each new header consumes 32bits of memory for
each stream, so don't push this limit too high.
Enables ('on') or disables ('off') sharing of idle connection pools between
threads for a same server. The default is to share them between threads in
order to minimize the number of persistent connections to a server, and to
optimize the connection reuse rate. But to help with debugging or when
suspecting a bug in HAProxy around connection reuse, it can be convenient to
forcefully disable this idle pool sharing between multiple threads, and force
this option to "off". The default is on. It is strongly recommended against
disabling this option without setting a conservative value on "pool-low-conn"
for all servers relying on connection reuse to achieve a high performance
level, otherwise connections might be closed very often as the thread count
increases.
tune.idletimer <timeout>
Sets the duration after which HAProxy will consider that an empty buffer is
probably associated with an idle stream. This is used to optimally adjust
some packet sizes while forwarding large and small data alternatively. The
decision to use splice() or to send large buffers in SSL is modulated by this
parameter. The value is in milliseconds between 0 and 65535. A value of zero
means that HAProxy will not try to detect idle streams. The default is 1000,
which seems to correctly detect end user pauses (e.g. read a page before
clicking). There should be no reason for changing this value. Please check
tune.ssl.maxrecord below.
tune.listener.default-shards { by-process | by-thread | by-group }
Normally, all "bind" lines will create a single shard, that is, a single
socket that all threads of the process will listen to. With many threads,
this is not very efficient, and may even induce some important overhead in
the kernel for updating the polling state or even distributing events to the
various threads. Modern operating systems support balancing of incoming
connections, a mechanism that will consist in permitting multiple sockets to
be bound to the same address and port, and to evenly distribute all incoming
connections to these sockets so that each thread only sees the connections
that are waiting in the socket it is bound to. This significantly reduces
kernel-side overhead and increases performance in the incoming connection
path. This is usually enabled in HAProxy using the "shards" setting on "bind"
lines, which defaults to 1, meaning that each listener will be unique in the
process. On systems with many processors, it may be more convenient to change
the default setting to "by-thread" in order to always create one listening
socket per thread, or "by-group" in order to always create one listening
socket per thread group. Be careful about the file descriptor usage with
"by-thread" as each listener will need as many sockets as there are threads.
Also some operating systems (e.g. FreeBSD) are limited to no more than 256
sockets on a same address. Note that "by-group" will remain equivalent to
"by-process" for default configurations involving a single thread group, and
will fall back to sharing the same socket on systems that do not support this
mechanism. The default is "by-group" with a fallback to "by-process" for
systems or socket families that do not support multiple bindings.
tune.listener.multi-queue { on | fair | off }
Enables ('on' / 'fair') or disables ('off') the listener's multi-queue accept
which spreads the incoming traffic to all threads a "bind" line is allowed to
run on instead of taking them for itself. This provides a smoother traffic
distribution and scales much better, especially in environments where threads
may be unevenly loaded due to external activity (network interrupts colliding
with one thread for example). The default mode, "on", optimizes the choice of
a thread by picking in a sample the one with the less connections. It is
often the best choice when connections are long-lived as it manages to keep
all threads busy. A second mode, "fair", instead cycles through all threads
regardless of their instant load level. It can be better suited for short-
lived connections, or on machines with very large numbers of threads where
the probability to find the least loaded thread with the first mode is low.
Finally it is possible to forcefully disable the redistribution mechanism
using "off" for troubleshooting, or for situations where connections are
short-lived and it is estimated that the operating system already provides a
good enough distribution. The default is "on".
This directive forces the Lua engine to execute a yield each <number> of
instructions executed. This permits interrupting a long script and allows the
HAProxy scheduler to process other tasks like accepting connections or
forwarding traffic. The default value is 10000 instructions. If HAProxy often
executes some Lua code but more responsiveness is required, this value can be
lowered. If the Lua code is quite long and its result is absolutely required
to process the data, the <number> can be increased.
Sets the maximum amount of RAM in megabytes per process usable by Lua. By
default it is zero which means unlimited. It is important to set a limit to
ensure that a bug in a script will not result in the system running out of
memory.
This is the execution timeout for the Lua sessions. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.
The "burst" execution timeout applies to any Lua handler. If the handler
fails to finish or yield before timeout is reached, it will be aborted to
prevent thread contention, to prevent traffic from not being served for too
long, and ultimately to prevent the process from crashing because of the
watchdog kicking in. Unlike other lua timeouts which are yield-cumulative,
burst-timeout will ensure that the time spent in a single lua execution
window does not exceed the configured timeout.

Yielding here means that the lua execution is effectively interrupted
either through an explicit call to lua-yielding function such as
core.(m)sleep() or core.yield(), or following an automatic forced-yield
(see tune.lua.forced-yield) and that it will be resumed later when the
related task is set for rescheduling. Not all lua handlers may yield: we have
to make a distinction between yieldable handlers and unyieldable handlers.

For yieldable handlers (tasks, actions..), reaching the timeout means
"tune.lua.forced-yield" might be too high for the system, reducing it
could improve the situation, but it could also be a good idea to check if
adding manual yields at some key points within the lua function helps or not.
It may also indicate that the handler is spending too much time in a specific
lua library function that cannot be interrupted.

For unyieldable handlers (lua converters, sample fetches), it could simply
indicate that the handler is doing too much computation, which could result
from an improper design given that such handlers, which often block the
request execution flow, are expected to terminate quickly to allow the
request processing to go through. A common resolution approach here would be
to try to better optimize the lua function for speed since decreasing
"tune.lua.forced-yield" won't help.

This timeout only counts the pure Lua runtime. If the Lua does a core.sleep,
the sleeping time is not taken in account. The default timeout is 1000ms.

Note: if a lua GC cycle is initiated from the handler (either explicitly
requested or automatically triggered by lua after some time), the GC cycle
time will also be accounted for.

Indeed, there is no way to deduce the GC cycle time, so this could lead to
some false positives on saturated systems (where GC is having hard time to
catch up and consumes most of the available execution runtime). If it were
to be the case, here are some resolution leads:

  - checking if the script could be optimized to reduce lua memory footprint
  - fine-tuning lua GC parameters and / or requesting manual GC cycles
    (see: https://www.lua.org/manual/5.4/manual.html#pdf-collectgarbage)
  - increasing tune.lua.burst-timeout

Setting value to 0 completely disables this protection.
This is the execution timeout for the Lua services. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.
Purpose is the same as "tune.lua.session-timeout", but this timeout is
dedicated to the tasks. By default, this timeout isn't set because a task may
remain alive during of the lifetime of HAProxy. For example, a task used to
check servers.
Enables ('on') or disables ('off') logging the output of LUA scripts via the
loggers applicable to the current proxy, if any.

Defaults to 'on'.
tune.lua.log.stderr { on | auto | off }
Enables ('on') or disables ('off') logging the output of LUA scripts via
stderr.
When set to 'auto', logging via stderr is conditionally 'on' if any of:

  - tune.lua.log.loggers is set to 'off'
  - the script is executed in a non-proxy context with no global logger
  - the script is executed in a proxy context with no logger attached

Please note that, when enabled, this logging is in addition to the logging
configured via tune.lua.log.loggers.

Defaults to 'auto'.
Sets the number of active checks per thread above which a thread will
actively try to search a less loaded thread to run the health check, or
queue it until the number of active checks running on it diminishes. The
default value is zero, meaning no such limit is set. It may be needed in
certain environments running an extremely large number of expensive checks
with many threads when the load appears unequal and may make health checks
to randomly time out on startup, typically when using OpenSSL 3.0 which is
about 20 times more CPU-intensive on health checks than older ones. This will
have for result to try to level the health check work across all threads. The
vast majority of configurations do not need to touch this parameter. Please
note that too low values may significantly slow down the health checking if
checks are slow to execute.
Sets the maximum number of consecutive connections a process may accept in a
row before switching to other work. In single process mode, higher numbers
used to give better performance at high connection rates, though this is not
the case anymore with the multi-queue. This value applies individually to
each listener, so that the number of processes a listener is bound to is
taken into account. This value defaults to 4 which showed best results. If a
significantly higher value was inherited from an ancient config, it might be
worth removing it as it will both increase performance and lower response
time. In multi-process mode, it is divided by twice the number of processes
the listener is bound to. Setting this value to -1 completely disables the
limitation. It should normally not be needed to tweak this value.
Sets the maximum amount of events that can be processed at once in a call to
the polling system. The default value is adapted to the operating system. It
has been noticed that reducing it below 200 tends to slightly decrease
latency at the expense of network bandwidth, and increasing it above 200
tends to trade latency for slightly increased bandwidth.
Sets the reserved buffer space to this size in bytes. The reserved space is
used for header rewriting or appending. The first reads on sockets will never
fill more than bufsize-maxrewrite. Historically it has defaulted to half of
bufsize, though that does not make much sense since there are rarely large
numbers of headers to add. Setting it too high prevents processing of large
requests or responses. Setting it too low prevents addition of new headers
to already large requests or to POST requests. It is generally wise to set it
to about 1024. It is automatically readjusted to half of bufsize if it is
larger than that. This means you don't have to worry about it when changing
bufsize.
Sets the per-thread amount of memory that will be kept hot in the local cache
and will never be recoverable by other threads. Access to this memory is very
fast (lockless), and having enough is critical to maintain a good performance
level under extreme thread contention. The value is expressed in bytes, and
the default value is configured at build time via CONFIG_HAP_POOL_CACHE_SIZE
which defaults to 524288 (512 kB). A larger value may increase performance in
some usage scenarios, especially when performance profiles show that memory
allocation is stressed a lot. Experience shows that a good value sits between
once to twice the per CPU core L2 cache size. Too large values will have a
negative impact on performance by making inefficient use of the L3 caches in
the CPUs, and will consume larger amounts of memory. It is recommended not to
change this value, or to proceed in small increments. In order to completely
disable the per-thread CPU caches, using a very small value could work, but
it is better to use "-dMno-cache" on the command-line.
Sets the size of the pattern lookup cache to <number> entries. This is an LRU
cache which reminds previous lookups and their results. It is used by ACLs
and maps on slow pattern lookups, namely the ones using the "sub", "reg",
"dir", "dom", "end", "bin" match methods as well as the case-insensitive
strings. It applies to pattern expressions which means that it will be able
to memorize the result of a lookup among all the patterns specified on a
configuration line (including all those loaded from files). It automatically
invalidates entries which are updated using HTTP actions or on the CLI. The
default cache size is set to 10000 entries, which limits its footprint to
about 5 MB per process/thread on 32-bit systems and 8 MB per process/thread
on 64-bit systems, as caches are thread/process local. There is a very low
risk of collision in this cache, which is in the order of the size of the
cache divided by 2^64. Typically, at 10000 requests per second with the
default cache size of 10000 entries, there's 1% chance that a brute force
attack could cause a single collision after 60 years, or 0.1% after 6 years.
This is considered much lower than the risk of a memory corruption caused by
aging components. If this is not acceptable, the cache can be disabled by
setting this parameter to 0.
Sets the maximum number of stick-table updates that haproxy will try to
process at once when sending messages. Retrieving the data for these updates
requires some locking operations which can be CPU intensive on highly
threaded machines if unbound, and may also increase the traffic latency
during the initial batched transfer between an older and a newer process.
Conversely low values may also incur higher CPU overhead, and take longer
to complete. The default value is 200 and it is suggested not to change it.
tune.pipesize <number>
Sets the kernel pipe buffer size to this size (in bytes). By default, pipes
are the default size for the system. But sometimes when using TCP splicing,
it can improve performance to increase pipe sizes, especially if it is
suspected that pipes are not filled and that many calls to splice() are
performed. This has an impact on the kernel's memory footprint, so this must
not be changed if impacts are not understood.
This setting sets the max number of file descriptors (in percentage) used by
HAProxy globally against the maximum number of file descriptors HAProxy can
use before we start killing idle connections when we can't reuse a connection
and we have to create a new one. The default is 25 (one quarter of the file
descriptor will mean that roughly half of the maximum front connections can
keep an idle connection behind, anything beyond this probably doesn't make
much sense in the general case when targeting connection reuse).
This setting sets the max number of file descriptors (in percentage) used by
HAProxy globally against the maximum number of file descriptors HAProxy can
use before we stop putting connection into the idle pool for reuse. The
default is 20.
Enables ('on') of disabled ('off') the zero-copy forwarding of data for the
pass-through multiplexer. To be used, the kernel splicing must also be
configured. It is enabled by default.
This settings defines the maximum number of buffers allocated for a QUIC
connection on data emission. By default, it is set to 30. QUIC buffers are
drained on ACK reception. This setting has a direct impact on the throughput
and memory consumption and can be adjusted according to an estimated round
time-trip. Each buffer is tune.bufsize.
Sets the QUIC max_idle_timeout transport parameters in milliseconds for
frontends which determines the period of time after which a connection silently
closes if it has remained inactive during an effective period of time deduced
from the two max_idle_timeout values announced by the two endpoints:
  - the minimum of the two values if both are not null,
  - the maximum if only one of them is not null,
  - if both values are null, this feature is disabled.

The default value is 30000.
Sets the QUIC initial_max_streams_bidi transport parameter for frontends.
This is the initial maximum number of bidirectional streams the remote peer
will be authorized to open. This determines the number of concurrent client
requests.

The default value is 100.
Sets the limit for which a single QUIC frame can be marked as lost. If
exceeded, the connection is considered as failing and is closed immediately.

The default value is 10.
tune.quic.reorder-ratio <0..100, in percent>
The ratio applied to the packet reordering threshold calculated. It may
trigger a high packet loss detection when too small.

The default value is 50.
Dynamically enables the Retry feature for all the configured QUIC listeners
as soon as this number of half open connections is reached. A half open
connection is a connection whose handshake has not already successfully
completed or failed. To be functional this setting needs a cluster secret to
be set, if not it will be silently ignored (see "cluster-secret" setting).
This setting will be also silently ignored if the use of QUIC Retry was
forced (see "quic-force-retry").

The default value is 100.

See https://www.rfc-editor.org/rfc/rfc9000.html#section-8.1.2 for more
information about QUIC retry.
tune.quic.socket-owner { connection | listener }
Specifies globally how QUIC connections will use socket for receive/send
operations. Connections can share listener socket or each connection can
allocate its own socket.

When default "connection" value is set, a dedicated socket will be allocated
by every QUIC connections. This option is the preferred one to achieve the
best performance with a large QUIC traffic. This is also the only way to
ensure soft-stop is conducted properly without data loss for QUIC connections
and cases of transient errors during sendto() operation are handled
efficiently. However, this relies on some advanced features from the UDP
network stack. If your platform is deemed not compatible, haproxy will
automatically switch to "listener" mode on startup. Please note that QUIC
listeners running on privileged ports may require to run as uid 0, or some
OS-specific tuning to permit the target uid to bind such ports, such as
system capabilities. See also the "setcap" global directive.

The "listener" value indicates that QUIC transfers will occur on the shared
listener socket. This option can be a good compromise for small traffic as it
allows to reduce FD consumption. However, performance won't be optimal due to
a higher CPU usage if listeners are shared across a lot of threads or a
large number of QUIC connections can be used simultaneously.

This setting is applied in conjunction with each "quic-socket" bind options.
If "connection" mode is used on global tuning, it will be activated for each
listener, unless its bind option is set to "listener". However, if "listener"
is used globally, it will be forced on every listener instance, regardless of
their individual configuration.
Enables ('on') of disabled ('off') the zero-copy sends of data for the QUIC
multiplexer. It is enabled by default.
For the kernel socket receive buffer size on non-connected sockets to this
size. This can be used QUIC in listener mode and log-forward on the frontend.
The default system buffers might sometimes be too small for sockets receiving
lots of aggregated traffic, causing some losses and possibly retransmits (in
case of QUIC), possibly slowing down connection establishment under heavy
traffic. The value is expressed in bytes, applied to each socket. In listener
mode, sockets are shared between all connections, and the total number of
sockets depends on the "shards" value of the "bind" line. There's no good
value, a good one corresponds to an expected size per connection multiplied
by the expected number of connections. The kernel may trim large values. See
also "tune.rcvbuf.client" and "tune.rcvbuf.server" for their connected socket
counter parts, as well as "tune.sndbuf.backend" and "tune.sndbuf.frontend"
for the send setting.
Forces the kernel socket receive buffer size on the client or the server side
to the specified value in bytes. This value applies to all TCP/HTTP frontends
and backends. It should normally never be set, and the default size (0) lets
the kernel auto-tune this value depending on the amount of available memory.
However it can sometimes help to set it to very low values (e.g. 4096) in
order to save kernel memory by preventing it from buffering too large amounts
of received data. Lower values will significantly increase CPU usage though.
HAProxy uses some hints to detect that a short read indicates the end of the
socket buffers. One of them is that a read returns more than <recv_enough>
bytes, which defaults to 10136 (7 segments of 1448 each). This default value
may be changed by this setting to better deal with workloads involving lots
of short messages such as telnet or SSH sessions.
Sets the maximum amount of task that can be processed at once when running
tasks. The default value depends on the number of threads but sits between 35
and 280, which tend to show the highest request rates and lowest latencies.
Increasing it may incur latency when dealing with I/Os, making it too small
can incur extra overhead. Higher thread counts benefit from lower values.
When experimenting with much larger values, it may be useful to also enable
tune.sched.low-latency and possibly tune.fd.edge-triggered to limit the
maximum latency to the lowest possible.
Enables ('on') or disables ('off') the low-latency task scheduler. By default
HAProxy processes tasks from several classes one class at a time as this is
the most efficient. But when running with large values of tune.runqueue-depth
this can have a measurable effect on request or connection latency. When this
low-latency setting is enabled, tasks of lower priority classes will always
be executed before other ones if they exist. This will permit to lower the
maximum latency experienced by new requests or connections in the middle of
massive traffic, at the expense of a higher impact on this large traffic.
For regular usage it is better to leave this off. The default value is off.
For the kernel socket send buffer size on non-connected sockets to this size.
This can be used for UNIX socket and UDP logging on the backend side, and for
QUIC in listener mode on the frontend. The default system buffers might
sometimes be too small for sockets shared between many connections (or log
senders), causing some losses and possibly retransmits, slowing down new
connection establishment under high traffic. The value is expressed in bytes,
applied to each socket. In listener mode, sockets are shared between all
connections, and the total number of sockets depends on the "shards" value of
the "bind" line. There's no good value, a good one corresponds to an expected
size per connection multiplied by the expected number of connections. The
kernel may trim large values. See also "tune.sndbuf.client" and
"tune.sndbuf.server" for their connected socket counter parts, as well as
"tune.rcvbuf.backend" and "tune.rcvbuf.frontend" for the receive setting.
Forces the kernel socket send buffer size on the client or the server side to
the specified value in bytes. This value applies to all TCP/HTTP frontends
and backends. It should normally never be set, and the default size (0) lets
the kernel auto-tune this value depending on the amount of available memory.
However it can sometimes help to set it to very low values (e.g. 4096) in
order to save kernel memory by preventing it from buffering too large amounts
of received data. Lower values will significantly increase CPU usage though.
Another use case is to prevent write timeouts with extremely slow clients due
to the kernel waiting for a large part of the buffer to be read before
notifying HAProxy again.
Sets the size of the global SSL session cache, in a number of blocks. A block
is large enough to contain an encoded session without peer certificate.  An
encoded session with peer certificate is stored in multiple blocks depending
on the size of the peer certificate. A block uses approximately 200 bytes of
memory (based on `sizeof(struct sh_ssl_sess_hdr) + SHSESS_BLOCK_MIN_SIZE`
calculation used for `shctx_init` function). The default value may be forced
at build time, otherwise defaults to 20000. When the cache is full, the most
idle entries are purged and reassigned. Higher values reduce the occurrence
of such a purge, hence the number of CPU-intensive SSL handshakes by ensuring
that all users keep their session as long as possible. All entries are
pre-allocated upon startup. Setting this value to 0 disables the SSL session
cache.
tune.ssl.capture-cipherlist-size <number> (deprecated)
Sets the maximum size of the buffer used for capturing client hello cipher
list, extensions list, elliptic curves list and elliptic curve point
formats. If the value is 0 (default value) the capture is disabled,
otherwise a buffer is allocated for each SSL/TLS connection.
Sets the maximum size of the Diffie-Hellman parameters used for generating
the ephemeral/temporary Diffie-Hellman key in case of DHE key exchange. The
final size will try to match the size of the server's RSA (or DSA) key (e.g,
a 2048 bits temporary DH key for a 2048 bits RSA key), but will not exceed
this maximum value. Only 1024 or higher values are allowed. Higher values
will increase the CPU load, and values greater than 1024 bits are not
supported by Java 7 and earlier clients. This value is not used if static
Diffie-Hellman parameters are supplied either directly in the certificate
file or by using the ssl-dh-param-file parameter.
If there is neither a default-dh-param nor a ssl-dh-param-file defined, and
if the server's PEM file of a given frontend does not specify its own DH
parameters, then DHE ciphers will be unavailable for this frontend.
This option disables SSL session cache sharing between all processes. It
should normally not be used since it will force many renegotiations due to
clients hitting a random process. But it may be required on some operating
systems where none of the SSL cache synchronization method may be used. In
this case, adding a first layer of hash-based load balancing before the SSL
layer might limit the impact of the lack of session sharing.
Sets the maximum amount of bytes passed to SSL_write() at any time. Default
value 0 means there is no limit. In contrast to tune.ssl.maxrecord this
settings will not be adjusted dynamically. Smaller records may decrease
throughput, but may be required when dealing with low-footprint clients.
tune.ssl.keylog { on | off }
This option activates the logging of the TLS keys. It should be used with
care as it will consume more memory per SSL session and could decrease
performances. This is disabled by default.

These sample fetches should be used to generate the SSLKEYLOGFILE that is
required to decipher traffic with wireshark.

https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format

The SSLKEYLOG is a series of lines which are formatted this way:

  <Label> <space> <ClientRandom> <space> <Secret>

The ClientRandom is provided by the %[ssl_fc_client_random,hex] sample
fetch, the secret and the Label could be find in the array below. You need
to generate a SSLKEYLOGFILE with all the labels in this array.

The following sample fetches are hexadecimal strings and does not need to be
converted.

SSLKEYLOGFILE Label             |  Sample fetches for the Secrets
--------------------------------|-----------------------------------------
CLIENT_EARLY_TRAFFIC_SECRET     |  %[ssl_fc_client_early_traffic_secret]
CLIENT_HANDSHAKE_TRAFFIC_SECRET |  %[ssl_fc_client_handshake_traffic_secret]
SERVER_HANDSHAKE_TRAFFIC_SECRET |  %[ssl_fc_server_handshake_traffic_secret]
CLIENT_TRAFFIC_SECRET_0         |  %[ssl_fc_client_traffic_secret_0]
SERVER_TRAFFIC_SECRET_0         |  %[ssl_fc_server_traffic_secret_0]
EXPORTER_SECRET                 |  %[ssl_fc_exporter_secret]
EARLY_EXPORTER_SECRET           |  %[ssl_fc_early_exporter_secret]

This is only available with OpenSSL 1.1.1, and useful with TLS1.3 session.

If you want to generate the content of a SSLKEYLOGFILE with TLS < 1.3, you
only need this line:

"CLIENT_RANDOM %[ssl_fc_client_random,hex] %[ssl_fc_session_key,hex]"
Sets how long a cached SSL session may remain valid. This time is expressed
in seconds and defaults to 300 (5 min). It is important to understand that it
does not guarantee that sessions will last that long, because if the cache is
full, the longest idle sessions will be purged despite their configured
lifetime. The real usefulness of this setting is to prevent sessions from
being used for too long.
Sets the maximum amount of bytes passed to SSL_write() at the beginning of
the data transfer. Default value 0 means there is no limit. Over SSL/TLS,
the client can decipher the data only once it has received a full record.
With large records, it means that clients might have to download up to 16kB
of data before starting to process them. Limiting the value can improve page
load times on browsers located over high latency or low bandwidth networks.
It is suggested to find optimal values which fit into 1 or 2 TCP segments
(generally 1448 bytes over Ethernet with TCP timestamps enabled, or 1460 when
timestamps are disabled), keeping in mind that SSL/TLS add some overhead.
Typical values of 1419 and 2859 gave good results during tests. Use
"strace -e trace=write" to find the best value. HAProxy will automatically
switch to this setting after an idle stream has been detected (see
tune.idletimer above). See also tune.ssl.hard-maxrecord.
Sets the size of the cache used to store generated certificates to <number>
entries. This is a LRU cache. Because generating a SSL certificate
dynamically is expensive, they are cached. The default cache size is set to
1000 entries.
Sets the maximum interval between two automatic updates of the same OCSP
response. This time is expressed in seconds and defaults to 3600 (1 hour). It
must be set to a higher value than "tune.ssl.ocsp-update.mindelay". See
option "ocsp-update" for more information about the auto update mechanism.
Sets the minimum interval between two automatic updates of the same OCSP
response. This time is expressed in seconds and defaults to 300 (5 minutes).
It is particularly useful for OCSP response that do not have explicit
expiration times. It must be set to a lower value than
"tune.ssl.ocsp-update.maxdelay". See option "ocsp-update" for more
information about the auto update mechanism.
Sets the number of stick-counters that may be tracked at the same time by a
connection or a request via "track-sc*" actions in "tcp-request" or
"http-request" rules. The default value is set at build time by the macro
MAX_SESS_STK_CTR, and defaults to 3. With this setting it is possible to
change the value and ignore the one passed at build time. Increasing this
value may be needed when porting complex configurations to haproxy, but users
are warned against the costs: each entry takes 16 bytes per connection and
16 bytes per request, all of which need to be allocated and zeroed for all
requests even when not used. As such a value of 10 will inflate the memory
consumption per request by 320 bytes and will cause this memory to be erased
for each request, which does have measurable CPU impacts. Conversely, when
no "track-sc" rules are used, the value may be lowered (0 being valid to
entirely disable stick-counters).
These five tunes help to manage the maximum amount of memory used by the
variables system. "global" limits the overall amount of memory available for
all scopes. "proc" limits the memory for the process scope, "sess" limits the
memory for the session scope, "txn" for the transaction scope, and "reqres"
limits the memory for each request or response processing.
Memory accounting is hierarchical, meaning more coarse grained limits include
the finer grained ones: "proc" includes "sess", "sess" includes "txn", and
"txn" includes "reqres".

For example, when "tune.vars.sess-max-size" is limited to 100,
"tune.vars.txn-max-size" and "tune.vars.reqres-max-size" cannot exceed
100 either. If we create a variable "txn.var" that contains 100 bytes,
all available space is consumed.
Notice that exceeding the limits at runtime will not result in an error
message, but values might be cut off or corrupted. So make sure to accurately
plan for the amount of space needed to store all your variables.
Sets the memLevel parameter in zlib initialization for each stream. It
defines how much memory should be allocated for the internal compression
state. A value of 1 uses minimum memory but is slow and reduces compression
ratio, a value of 9 uses maximum memory for optimal speed. Can be a value
between 1 and 9. The default value is 8.
Sets the window size (the size of the history buffer) as a parameter of the
zlib initialization for each stream. Larger values of this parameter result
in better compression at the expense of memory usage. Can be a value between
8 and 15. The default value is 15.

3.3. Debugging

anonkey <key>
This sets the global anonymizing key to <key>, which must be a 32-bit number
between 0 and 4294967295. This is the key that will be used by default by CLI
commands when anonymized mode is enabled. This key may also be set at runtime
from the CLI command "set anon global-key". See also command line argument
"-dC" in the management manual.
This speeds up the old process exit upon reload by skipping the releasing of
memory objects and listeners, since all of these are reclaimed by the
operating system at the process' death. The gains are only marginal (in the
order of a few hundred milliseconds for huge configurations at most). The
main target usage in fact is when a bug is spotted in the deinit() code, as
this allows to bypass it. It is better not to use this unless instructed to
do so by developers.
Do not display any message during startup. It is equivalent to the command-
line argument "-q".
When this option is set, HAProxy will refuse to start if any warning was
emitted while processing the configuration. It is highly recommended to set
this option on configurations that are not changed often, as it helps detect
subtle mistakes and keep the configuration clean and forward-compatible. Note
that "haproxy -c" will also report errors in such a case. This option is
equivalent to command line argument "-dW".

3.4. Userlists

It is possible to control access to frontend/backend/listen sections or to
http stats by allowing only authenticated and authorized users. To do this,
it is required to create at least one userlist and to define users.
userlist <listname>
Creates new userlist with name <listname>. Many independent userlists can be
used to store authentication & authorization data for independent customers.
group <groupname> [users <user>,<user>,(...)]
Adds group <groupname> to the current userlist. It is also possible to
attach users to this group by using a comma separated list of names
proceeded by "users" keyword.
user <username> [password|insecure-password <password>] [groups <group>,<group>,(...)]
Adds user <username> to the current userlist. Both secure (encrypted) and
insecure (unencrypted) passwords can be used. Encrypted passwords are
evaluated using the crypt(3) function, so depending on the system's
capabilities, different algorithms are supported. For example, modern Glibc
based Linux systems support MD5, SHA-256, SHA-512, and, of course, the
classic DES-based method of encrypting passwords.

Attention: Be aware that using encrypted passwords might cause significantly
increased CPU usage, depending on the number of requests, and the algorithm
used. For any of the hashed variants, the password for each request must
be processed through the chosen algorithm, before it can be compared to the
value specified in the config file. Most current algorithms are deliberately
designed to be expensive to compute to achieve resistance against brute
force attacks. They do not simply salt/hash the clear text password once,
but thousands of times. This can quickly become a major factor in HAProxy's
overall CPU consumption, and can even lead to application crashes!

To address the high CPU usage of hash functions, one approach is to reduce
the number of rounds of the hash function (SHA family algorithms) or decrease
the "cost" of the function, if the algorithm supports it.

As a side note, musl (e.g. Alpine Linux) implementations are known to be
slower than their glibc counterparts when calculating hashes, so you might
want to consider this aspect too.
Example:
userlist L1
  group G1 users tiger,scott
  group G2 users xdb,scott

  user tiger password $6$k6y3o.eP$JlKBx9za9667qe4(...)xHSwRv6J.C0/D7cV91
  user scott insecure-password elgato
  user xdb insecure-password hello

userlist L2
  group G1
  group G2

  user tiger password $6$k6y3o.eP$JlKBx(...)xHSwRv6J.C0/D7cV91 groups G1
  user scott insecure-password elgato groups G1,G2
  user xdb insecure-password hello groups G2
Please note that both lists are functionally identical.

3.5. Peers

It is possible to propagate entries of any data-types in stick-tables between
several HAProxy instances over TCP connections in a multi-master fashion. Each
instance pushes its local updates and insertions to remote peers. The pushed
values overwrite remote ones without aggregation. As an exception, the data
type "conn_cur" is never learned from peers, as it is supposed to reflect local
values. Earlier versions used to synchronize it and to cause negative values in
active-active setups, and always-growing values upon reloads or active-passive
switches because the local value would reflect more connections than locally
present. This information, however, is pushed so that monitoring systems can
watch it.

Interrupted exchanges are automatically detected and recovered from the last
known point. In addition, during a soft restart, the old process connects to
the new one using such a TCP connection to push all its entries before the new
process tries to connect to other peers. That ensures very fast replication
during a reload, it typically takes a fraction of a second even for large
tables.

Note that Server IDs are used to identify servers remotely, so it is important
that configurations look similar or at least that the same IDs are forced on
each server on all participants.
peers <peersect>
Creates a new peer list with name <peersect>. It is an independent section,
which is referenced by one or more stick-tables.
bind [<address>]:port [param*]
bind /<path> [param*]
Defines the binding parameters of the local peer of this "peers" section.
Such lines are not supported with "peer" line in the same "peers" section.
Disables a peers section. It disables both listening and any synchronization
related to this section. This is provided to disable synchronization of stick
tables without having to comment out all "peers" references.
default-bind [param*]
Defines the binding parameters for the local peer, excepted its address.
Change default options for a server in a "peers" section.
Arguments:
<param*>  is a list of parameters for this server. The "default-server"
          keyword accepts an important number of options and has a complete
          section dedicated to it. In a peers section, the transport
          parameters of a "default-server" line are supported. Please refer
          to section 5 for more details, and the "server" keyword below in
          this section for some of the restrictions.
This re-enables a peers section which was previously disabled via the
"disabled" keyword.
log <target> [len <length>] [format <format>] [sample <ranges>:<sample_size>] <facility> [<level> [<minlevel>]]
"peers" sections support the same "log" keyword as for the proxies to
log information about the "peers" listener. See "log" option for proxies for
more details.
peer <peername> [<address>]:port [param*]
peer <peername> /<path> [param*]
Defines a peer inside a peers section.
If <peername> is set to the local peer name (by default hostname, or forced
using "-L" command line option or "localpeer" global configuration setting),
HAProxy will listen for incoming remote peer connection on the provided
address.  Otherwise, the address defines where to connect to in order to join
the remote peer, and <peername> is used at the protocol level to identify and
validate the remote peer on the server side.

During a soft restart, local peer address is used by the old instance to
connect the new one and initiate a complete replication (teaching process).

It is strongly recommended to have the exact same peers declaration on all
peers and to only rely on the "-L" command line argument or the "localpeer"
global configuration setting to change the local peer name. This makes it
easier to maintain coherent configuration files across all peers.

You may want to reference some environment variables in the address
parameter, see section 2.3 about environment variables.

Note: "peer" keyword may transparently be replaced by "server" keyword (see
"server" keyword explanation below).
server <peername> [<address>:<port>] [param*]
server <peername> [/<path>] [param*]
As previously mentioned, "peer" keyword may be replaced by "server" keyword
with a support for all "server" parameters found in 5.2 paragraph that are
related to transport settings. If the underlying peer is local, the address
parameter must not be present; it must be provided on a "bind" line (see
"bind" keyword of this "peers" section).

A number of "server" parameters are irrelevant for "peers" sections. Peers by
nature do not support dynamic host name resolution nor health checks, hence
parameters like "init_addr", "resolvers", "check", "agent-check", or "track"
are not supported. Similarly, there is no load balancing nor stickiness, thus
parameters such as "weight" or "cookie" have no effect.
Example:
 # The old way.
 peers mypeers
     peer haproxy1 192.168.0.1:1024
     peer haproxy2 192.168.0.2:1024
     peer haproxy3 10.2.0.1:1024

 backend mybackend
     mode tcp
     balance roundrobin
     stick-table type ip size 20k peers mypeers
     stick on src

     server srv1 192.168.0.30:80
     server srv2 192.168.0.31:80

Example:
  peers mypeers
     bind 192.168.0.1:1024 ssl crt mycerts/pem
     default-server ssl verify none
     server haproxy1 #local peer
     server haproxy2 192.168.0.2:1024
     server haproxy3 10.2.0.1:1024
shards <shards>
In some configurations, one would like to distribute the stick-table contents
to some peers in place of sending all the stick-table contents to each peer
declared in the "peers" section. In such cases, "shards" specifies the
number of peer involved in this stick-table contents distribution.
See also "shard" server parameter.
table <tablename> type {ip | integer | string [len <length>] | binary [len <length>]} size <size> [expire <expire>] [write-to <wtable>] [nopurge] [store <data_type>]*
Configure a stickiness table for the current section. This line is parsed
exactly the same way as the "stick-table" keyword in others section, except
for the "peers" argument which is not required here and with an additional
mandatory first parameter to designate the stick-table. Contrary to others
sections, there may be several "table" lines in "peers" sections (see also
"stick-table" keyword).

Also be aware of the fact that "peers" sections have their own stick-table
namespaces to avoid collisions between stick-table names identical in
different "peers" section. This is internally handled prepending the "peers"
sections names to the name of the stick-tables followed by a '/' character.
If somewhere else in the configuration file you have to refer to such
stick-tables declared in "peers" sections you must use the prefixed version
of the stick-table name as follows:

    peers mypeers
        peer A ...
        peer B ...
        table t1 ...

    frontend fe1
        tcp-request content track-sc0 src table mypeers/t1

This is also this prefixed version of the stick-table names which must be
used to refer to stick-tables through the CLI.

About "peers" protocol, as only "peers" belonging to the same section may
communicate with each others, there is no need to do such a distinction.
Several "peers" sections may declare stick-tables with the same name.
This is shorter version of the stick-table name  which is sent over the network.
There is only a '/' character as prefix to avoid stick-table name collisions between
stick-tables declared as backends and stick-table declared in "peers" sections
as follows in this weird but supported configuration:

    peers mypeers
        peer A ...
        peer B ...
        table t1 type string size 10m store gpc0

    backend t1
        stick-table type string size 10m store gpc0 peers mypeers

Here "t1" table declared in "mypeers" section has "mypeers/t1" as global name.
"t1" table declared as a backend as "t1" as global name. But at peer protocol
level the former table is named "/t1", the latter is again named "t1".

3.6. Mailers

It is possible to send email alerts when the state of servers changes.
If configured email alerts are sent to each mailer that is configured
in a mailers section. Email is sent to mailers using SMTP.
mailers <mailersect>
Creates a new mailer list with the name <mailersect>. It is an
independent section which is referenced by one or more proxies.
mailer <mailername> <ip>:<port>
Defines a mailer inside a mailers section.
Example:
mailers mymailers
    mailer smtp1 192.168.0.1:587
    mailer smtp2 192.168.0.2:587

backend mybackend
    mode tcp
    balance roundrobin

    email-alert mailers mymailers
    email-alert from test1@horms.org
    email-alert to test2@horms.org

    server srv1 192.168.0.30:80
    server srv2 192.168.0.31:80
Defines the time available for a mail/connection to be made and send to
the mail-server. If not defined the default value is 10 seconds. To allow
for at least two SYN-ACK packets to be send during initial TCP handshake it
is advised to keep this value above 4 seconds.
Example:
mailers mymailers
    timeout mail 20s
    mailer smtp1 192.168.0.1:587

3.7. Programs

In master-worker mode, it is possible to launch external binaries with the
master, these processes are called programs. These programs are launched and
managed the same way as the workers.

During a reload of HAProxy, those processes are dealing with the same
sequence as a worker:

  - the master is re-executed
  - the master sends a SIGUSR1 signal to the program
  - if "option start-on-reload" is not disabled, the master launches a new
    instance of the program

During a stop, or restart, a SIGTERM is sent to the programs.
program <name>
This is a new program section, this section will create an instance <name>
which is visible in "show proc" on the master CLI. (See "9.4. Master CLI" in
the management guide).
command <command> [arguments*]
Define the command to start with optional arguments. The command is looked
up in the current PATH if it does not include an absolute path. This is a
mandatory option of the program section. Arguments containing spaces must
be enclosed in quotes or double quotes or be prefixed by a backslash.
user <user name>
Changes the executed command user ID to the <user name> from /etc/passwd.
See also "group".
group <group name>
Changes the executed command group ID to the <group name> from /etc/group.
See also "user".
Start (or not) a new instance of the program upon a reload of the master.
The default is to start a new instance. This option may only be used in a
program section.

3.8. HTTP-errors

It is possible to globally declare several groups of HTTP errors, to be
imported afterwards in any proxy section. Same group may be referenced at
several places and can be fully or partially imported.
Create a new http-errors group with the name <name>. It is an independent
section that may be referenced by one or more proxies using its name.
errorfile <code> <file>
Associate a file contents to an HTTP error code
Arguments :
<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 401, 403, 404, 405, 407, 408, 410,
          425, 429, 500, 501, 502, 503, and 504.

<file>    designates a file containing the full HTTP response. It is
          recommended to follow the common practice of appending ".http" to
          the filename so that people do not confuse the response with HTML
          error pages, and to use absolute paths, since files are read
          before any chroot is performed.
Please referrers to "errorfile" keyword in section 4 for details.
Example:
http-errors website-1
    errorfile 400 /etc/haproxy/errorfiles/site1/400.http
    errorfile 404 /etc/haproxy/errorfiles/site1/404.http
    errorfile 408 /dev/null  # work around Chrome pre-connect bug

http-errors website-2
    errorfile 400 /etc/haproxy/errorfiles/site2/400.http
    errorfile 404 /etc/haproxy/errorfiles/site2/404.http
    errorfile 408 /dev/null  # work around Chrome pre-connect bug

3.9. Rings

It is possible to globally declare ring-buffers, to be used as target for log
servers or traces.
ring <ringname>
Creates a new ring-buffer with name <ringname>.
This replaces the regular memory allocation by a RAM-mapped file to store the
ring. This can be useful for collecting traces or logs for post-mortem
analysis, without having to attach a slow client to the CLI. Newer contents
will automatically replace older ones so that the latest contents are always
available. The contents written to the ring will be visible in that file once
the process stops (most often they will even be seen very soon after but
there is no such guarantee since writes are not synchronous).

When this option is used, the total storage area is reduced by the size of
the "struct ring" that starts at the beginning of the area, and that is
required to recover the area's contents. The file will be created with the
starting user's ownership, with mode 0600 and will be of the size configured
by the "size" directive. When the directive is parsed (thus even during
config checks), any existing non-empty file will first be renamed with the
extra suffix ".bak", and any previously existing file with suffix ".bak" will
be removed. This ensures that instant reload or restart of the process will
not wipe precious debugging information, and will leave time for an admin to
spot this new ".bak" file and to archive it if needed. As such, after a crash
the file designated by <path> will contain the freshest information, and if
the service is restarted, the "<path>.bak" file will have it instead. This
means that the total storage capacity required will be double of the ring
size. Failures to rotate the file are silently ignored, so placing the file
into a directory without write permissions will be sufficient to avoid the
backup file if not desired.

WARNING: there are stability and security implications in using this feature.
First, backing the ring to a slow device (e.g. physical hard drive) may cause
perceptible slowdowns during accesses, and possibly even panics if too many
threads compete for accesses. Second, an external process modifying the area
could cause the haproxy process to crash or to overwrite some of its own
memory with traces. Third, if the file system fills up before the ring,
writes to the ring may cause the process to crash.

The information present in this ring are structured and are NOT directly
readable using a text editor (even though most of it looks barely readable).
The output of this file is only intended for developers.
The description is an optional description string of the ring. It will
appear on CLI. By default, <name> is reused to fill this field.
format <format>
Format used to store events into the ring buffer.
Arguments:
<format> is the log format used when generating syslog messages. It may be
         one of the following :

  iso     A message containing only the ISO date, followed by the text.
          The PID, process name and system name are omitted. This is
          designed to be used with a local log server.

  local   Analog to rfc3164 syslog message format except that hostname
          field is stripped. This is the default.
          Note: option "log-send-hostname" switches the default to
          rfc3164.

  raw     A message containing only the text. The level, PID, date, time,
          process name and system name are omitted. This is designed to be
          used in containers or during development, where the severity
          only depends on the file descriptor used (stdout/stderr). This
          is the default.

  rfc3164 The RFC3164 syslog message format.
          (https://tools.ietf.org/html/rfc3164)

  rfc5424 The RFC5424 syslog message format.
          (https://tools.ietf.org/html/rfc5424)

  short   A message containing only a level between angle brackets such as
          '<3>', followed by the text. The PID, date, time, process name
          and system name are omitted. This is designed to be used with a
          local log server. This format is compatible with what the systemd
          logger consumes.

 priority A message containing only a level plus syslog facility between angle
          brackets such as '<63>', followed by the text. The PID, date, time,
          process name and system name are omitted. This is designed to be used
          with a local log server.

  timed   A message containing only a level between angle brackets such as
          '<3>', followed by ISO date and by the text. The PID, process
          name and system name are omitted. This is designed to be
          used with a local log server.
maxlen <length>
The maximum length of an event message stored into the ring,
including formatted header. If an event message is longer than
<length>, it will be truncated to this length.
server <name> <address> [param*]
Used to configure a syslog tcp server to forward messages from ring buffer.
This supports for all "server" parameters found in 5.2 paragraph. Some of
these parameters are irrelevant for "ring" sections. Important point: there
is little reason to add more than one server to a ring, because all servers
will receive the exact same copy of the ring contents, and as such the ring
will progress at the speed of the slowest server. If one server does not
respond, it will prevent old messages from being purged and may block new
messages from being inserted into the ring. The proper way to send messages
to multiple servers is to use one distinct ring per log server, not to
attach multiple servers to the same ring. Note that specific server directive
"log-proto" is used to set the protocol used to send messages.
size <size>
This is the optional size in bytes for the ring-buffer. Default value is
set to BUFSIZE.
timeout connect <timeout>
Set the maximum time to wait for a connection attempt to a server to succeed.
Arguments :
<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.
timeout server <timeout>
Set the maximum time for pending data staying into output buffer.
Arguments :
<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.
Example:
global
    log ring@myring local7

ring myring
    description "My local buffer"
    format rfc3164
    maxlen 1200
    size 32764
    timeout connect 5s
    timeout server 10s
    server mysyslogsrv 127.0.0.1:6514 log-proto octet-count

3.10. Log forwarding

It is possible to declare one or multiple log forwarding section,
HAProxy will forward all received log messages to a log servers list.
Creates a new log forwarder proxy identified as <name>.
backlog <conns>
Give hints to the system about the approximate listen backlog desired size
on connections accept.
bind <addr> [param*]
Used to configure a stream log listener to receive messages to forward.
This supports the "bind" parameters found in 5.1 paragraph including
those about ssl but some statements such as "alpn" may be irrelevant for
syslog protocol over TCP.
Those listeners support both "Octet Counting" and "Non-Transparent-Framing"
modes as defined in rfc-6587.
dgram-bind <addr> [param*]
Used to configure a datagram log listener to receive messages to forward.
Addresses must be in IPv4 or IPv6 form,followed by a port. This supports
for some of the "bind" parameters found in 5.1 paragraph among which
"interface", "namespace" or "transparent", the other ones being
silently ignored as irrelevant for UDP/syslog case.
log <target> [len <length>] [format <format>] [sample <ranges>:<sample_size>] <facility> [<level> [<minlevel>]]
Used to configure target log servers. See more details on proxies
documentation.
If no format specified, HAProxy tries to keep the incoming log format.
Configured facility is ignored, except if incoming message does not
present a facility but one is mandatory on the outgoing format.
If there is no timestamp available in the input format, but the field
exists in output format, HAProxy will use the local date.
Example:
global
   log stderr format iso local7

ring myring
    description "My local buffer"
    format rfc5424
    maxlen 1200
    size 32764
    timeout connect 5s
    timeout server 10s
    # syslog tcp server
    server mysyslogsrv 127.0.0.1:514 log-proto octet-count

log-forward sylog-loadb
    dgram-bind 127.0.0.1:1514
    bind 127.0.0.1:1514
    # all messages on stderr
    log global
    # all messages on local tcp syslog server
    log ring@myring local0
    # load balance messages on 4 udp syslog servers
    log 127.0.0.1:10001 sample 1:4 local0
    log 127.0.0.1:10002 sample 2:4 local0
    log 127.0.0.1:10003 sample 3:4 local0
    log 127.0.0.1:10004 sample 4:4 local0
maxconn <conns>
Fix the maximum number of concurrent connections on a log forwarder.
10 is the default.
timeout client <timeout>
Set the maximum inactivity time on the client side.

3.11. HTTPClient tuning

HTTPClient is an internal HTTP library, it can be used by various subsystems,
for example in LUA scripts. HTTPClient is not used in the data path, in other
words it has nothing with HTTP traffic passing through HAProxy.
Disable the DNS resolution of the httpclient. Prevent the creation of the
"default" resolvers section.

Default value is off.
This option defines the resolvers section with which the httpclient will try
to resolve.

Default option is the "default" resolvers ID. By default, if this option is
not used, it will simply disable the resolving if the section is not found.

However, when this option is explicitly enabled it will trigger a
configuration error if it fails to load.
This option allows to chose which family of IP you want when resolving,
which is convenient when IPv6 is not available on your network. Default
option is "ipv6".
This option allows to configure the number of retries attempt of the
httpclient when a request failed. This does the same as the "retries" keyword
in a backend.

Default value is 3.
This option defines the ca-file which should be used to verify the server
certificate. It takes the same parameters as the "ca-file" option on the
server line.

By default and when this option is not used, the value is
"@system-ca" which tries to load the CA of the system. If it fails the SSL
will be disabled for the httpclient.

However, when this option is explicitly enabled it will trigger a
configuration error if it fails.
httpclient.ssl.verify [none|required]
Works the same way as the verify option on server lines. If specified to 'none',
servers certificates are not verified. Default option is "required".

By default and when this option is not used, the value is
"required". If it fails the SSL will be disabled for the httpclient.

However, when this option is explicitly enabled it will trigger a
configuration error if it fails.
Set the maximum time to wait for a connection attempt by default for the
httpclient.
Arguments :
<timeout> is the timeout value specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.
The default value is 5000ms.
Proxy configuration can be located in a set of sections :
 - defaults [<name>] [ from <defaults_name> ]
 - frontend <name>   [ from <defaults_name> ]
 - backend  <name>   [ from <defaults_name> ]
 - listen   <name>   [ from <defaults_name> ]

A "frontend" section describes a set of listening sockets accepting client
connections.

A "backend" section describes a set of servers to which the proxy will connect
to forward incoming connections.

A "listen" section defines a complete proxy with its frontend and backend
parts combined in one section. It is generally useful for TCP-only traffic.

A "defaults" section resets all settings to the documented ones and presets new
ones for use by subsequent sections. All of "frontend", "backend" and "listen"
sections always take their initial settings from a defaults section, by default
the latest one that appears before the newly created section. It is possible to
explicitly designate a specific "defaults" section to load the initial settings
from by indicating its name on the section line after the optional keyword
"from". While "defaults" section do not impose a name, this use is encouraged
for better readability. It is also the only way to designate a specific section
to use instead of the default previous one. Since "defaults" section names are
optional, by default a very permissive check is applied on their name and these
are even permitted to overlap. However if a "defaults" section is referenced by
any other section, its name must comply with the syntax imposed on all proxy
names, and this name must be unique among the defaults sections. Please note
that regardless of what is currently permitted, it is recommended to avoid
duplicate section names in general and to respect the same syntax as for proxy
names. This rule might be enforced in a future version. In addition, a warning
is emitted if a defaults section is explicitly used by a proxy while it is also
implicitly used by another one because it is the last one defined. It is highly
encouraged to not mix both usages by always using explicit references or by
adding a last common defaults section reserved for all implicit uses.

Note that it is even possible for a defaults section to take its initial
settings from another one, and as such, inherit settings across multiple levels
of defaults sections. This can be convenient to establish certain configuration
profiles to carry groups of default settings (e.g. TCP vs HTTP or short vs long
timeouts) but can quickly become confusing to follow.

All proxy names must be formed from upper and lower case letters, digits,
'-' (dash), '_' (underscore) , '.' (dot) and ':' (colon). ACL names are
case-sensitive, which means that "www" and "WWW" are two different proxies.

Historically, all proxy names could overlap, it just caused troubles in the
logs. Since the introduction of content switching, it is mandatory that two
proxies with overlapping capabilities (frontend/backend) have different names.
However, it is still permitted that a frontend and a backend share the same
name, as this configuration seems to be commonly encountered.

Right now, two major proxy modes are supported : "tcp", also known as layer 4,
and "http", also known as layer 7. In layer 4 mode, HAProxy simply forwards
bidirectional traffic between two sides. In layer 7 mode, HAProxy analyzes the
protocol, and can interact with it by allowing, blocking, switching, adding,
modifying, or removing arbitrary contents in requests or responses, based on
arbitrary criteria.

In HTTP mode, the processing applied to requests and responses flowing over
a connection depends in the combination of the frontend's HTTP options and
the backend's. HAProxy supports 3 connection modes :

  - KAL : keep alive ("option http-keep-alive") which is the default mode : all
    requests and responses are processed, and connections remain open but idle
    between responses and new requests.

  - SCL: server close ("option http-server-close") : the server-facing
    connection is closed after the end of the response is received, but the
    client-facing connection remains open.

  - CLO: close ("option httpclose"): the connection is closed after the end of
    the response and "Connection: close" appended in both directions.

The effective mode that will be applied to a connection passing through a
frontend and a backend can be determined by both proxy modes according to the
following matrix, but in short, the modes are symmetric, keep-alive is the
weakest option and close is the strongest.

                   Backend mode

                | KAL | SCL | CLO
            ----+-----+-----+----
            KAL | KAL | SCL | CLO
            ----+-----+-----+----
   mode     SCL | SCL | SCL | CLO
            ----+-----+-----+----
            CLO | CLO | CLO | CLO

It is possible to chain a TCP frontend to an HTTP backend. It is pointless if
only HTTP traffic is handled. But it may be used to handle several protocols
within the same frontend. In this case, the client's connection is first handled
as a raw tcp connection before being upgraded to HTTP. Before the upgrade, the
content processings are performend on raw data. Once upgraded, data is parsed
and stored using an internal representation called HTX and it is no longer
possible to rely on raw representation. There is no way to go back.

There are two kind of upgrades, in-place upgrades and destructive upgrades. The
first ones involves a TCP to HTTP/1 upgrade. In HTTP/1, the request
processings are serialized, thus the applicative stream can be preserved. The
second one involves a TCP to HTTP/2 upgrade. Because it is a multiplexed
protocol, the applicative stream cannot be associated to any HTTP/2 stream and
is destroyed. New applicative streams are then created when HAProxy receives
new HTTP/2 streams at the lower level, in the H2 multiplexer. It is important
to understand this difference because that drastically changes the way to
process data. When an HTTP/1 upgrade is performed, the content processings
already performed on raw data are neither lost nor reexecuted while for an
HTTP/2 upgrade, applicative streams are distinct and all frontend rules are
evaluated systematically on each one. And as said, the first stream, the TCP
one, is destroyed, but only after the frontend rules were evaluated.

There is another importnat point to understand when HTTP processings are
performed from a TCP proxy. While HAProxy is able to parse HTTP/1 in-fly from
tcp-request content rules, it is not possible for HTTP/2. Only the HTTP/2
preface can be parsed. This is a huge limitation regarding the HTTP content
analysis in TCP. Concretely it is only possible to know if received data are
HTTP. For instance, it is not possible to choose a backend based on the Host
header value while it is trivial in HTTP/1. Hopefully, there is a solution to
mitigate this drawback.

There are two ways to perform an HTTP upgrade. The first one, the historical
method, is to select an HTTP backend. The upgrade happens when the backend is
set. Thus, for in-place upgrades, only the backend configuration is considered
in the HTTP data processing. For destructive upgrades, the applicative stream
is destroyed, thus its processing is stopped. With this method, possibilities
to choose a backend with an HTTP/2 connection are really limited, as mentioned
above, and a bit useless because the stream is destroyed. The second method is
to upgrade during the tcp-request content rules evaluation, thanks to the
"switch-mode http" action. In this case, the upgrade is performed in the
frontend context and it is possible to define HTTP directives in this
frontend. For in-place upgrades, it offers all the power of the HTTP analysis
as soon as possible. It is not that far from an HTTP frontend. For destructive
upgrades, it does not change anything except it is useless to choose a backend
on limited information. It is of course the recommended method. Thus, testing
the request protocol from the tcp-request content rules to perform an HTTP
upgrade is enough. All the remaining HTTP manipulation may be moved to the
frontend http-request ruleset. But keep in mind that tcp-request content rules
remains evaluated on each streams, that can't be changed.

4.1. Proxy keywords matrix

The following list of keywords is supported. Most of them may only be used in a
limited set of section types. Some of them are marked as "deprecated" because
they are inherited from an old syntax which may be confusing or functionally
limited, and there are new recommended keywords to replace them. Keywords
marked with "(*)" can be optionally inverted using the "no" prefix, e.g. "no
option contstats". This makes sense when the option has been enabled by default
and must be disabled for a specific instance. Such options may also be prefixed
with "default" in order to restore default settings regardless of what has been
specified in a previous "defaults" section. Keywords supported in defaults
sections marked with "(!)" are only supported in named defaults sections, not
anonymous ones.
keyworddefaultsfrontendlistenbackend
aclX (!)XXX
backlogXXX 
balanceX XX
bind XX 
capture cookie XX 
capture request header XX 
capture response header XX 
clitcpka-cntXXX 
clitcpka-idleXXX 
clitcpka-intvlXXX 
compressionXXXX
cookieX XX
declare capture XX 
default-serverX XX
default_backendXXX 
description XXX
disabledXXXX
dispatch  XX
email-alert fromXXXX
email-alert levelXXXX
keyworddefaultsfrontendlistenbackend
email-alert mailersXXXX
email-alert myhostnameXXXX
email-alert toXXXX
enabledXXXX
errorfileXXXX
errorfilesXXXX
errorlocXXXX
errorloc302XXXX
errorloc303XXXX
error-log-formatXXX 
force-persist  XX
filter XXX
fullconnX XX
hash-typeX XX
http-after-responseX (!)XXX
http-check commentX XX
http-check connectX XX
http-check disable-on-404X XX
http-check expectX XX
http-check sendX XX
keyworddefaultsfrontendlistenbackend
http-check send-stateX XX
http-check set-varX XX
http-check unset-varX XX
http-errorXXXX
http-requestX (!)XXX
http-responseX (!)XXX
http-reuseX XX
http-send-name-headerX XX
id XXX
ignore-persist  XX
load-server-state-from-fileX XX
(*)logXXXX
log-formatXXX 
log-format-sdXXX 
log-tagXXXX
max-keep-alive-queueX XX
max-session-srv-connsXXX 
maxconnXXX 
modeXXXX
monitor fail XX 
keyworddefaultsfrontendlistenbackend
monitor-uriXXX 
(*)option abortoncloseX XX
(*)option accept-invalid-http-requestXXX 
(*)option accept-invalid-http-responseX XX
(*)option allbackupsX XX
(*)option checkcacheX XX
(*)option clitcpkaXXX 
(*)option contstatsXXX 
(*)option disable-h2-upgradeXXX 
(*)option dontlog-normalXXX 
(*)option dontlognullXXX 
option forwardforXXXX
(*)option forwardedX XX
(*)option h1-case-adjust-bogus-clientXXX 
(*)option h1-case-adjust-bogus-serverX XX
(*)option http-buffer-requestXXXX
(*)option http-ignore-probesXXX 
(*)option http-keep-aliveXXXX
(*)option http-no-delayXXXX
(*)option http-pretend-keepaliveX XX
keyworddefaultsfrontendlistenbackend
option http-restrict-req-hdr-namesXXXX
(*)option http-server-closeXXXX
(*)option http-use-proxy-headerXXX 
option httpchkX XX
(*)option httpcloseXXXX
option httplogXXX 
option httpslogXXX 
(*)option independent-streamsXXXX
option ldap-checkX XX
option external-checkX XX
(*)option log-health-checksX XX
(*)option log-separate-errorsXXX 
(*)option logasapXXX 
option mysql-checkX XX
(*)option nolingerXXXX
option originaltoXXXX
(*)option persistX XX
option pgsql-checkX XX
(*)option prefer-last-serverX XX
(*)option redispatchX XX
keyworddefaultsfrontendlistenbackend
option redis-checkX XX
option smtpchkX XX
(*)option socket-statsXXX 
(*)option splice-autoXXXX
(*)option splice-requestXXXX
(*)option splice-responseXXXX
option spop-checkX XX
(*)option srvtcpkaX XX
option ssl-hello-chkX XX
option tcp-checkX XX
(*)option tcp-smart-acceptXXX 
(*)option tcp-smart-connectX XX
option tcpkaXXXX
option tcplogXXXX
(*)option transparentX XX
(*)option idle-close-on-responseXXX 
external-check commandX XX
external-check pathX XX
persist rdp-cookieX XX
rate-limit sessionsXXX 
keyworddefaultsfrontendlistenbackend
redirect XXX
retriesX XX
retry-onX XX
server  XX
server-state-file-nameX XX
server-template  XX
sourceX XX
srvtcpka-cntX XX
srvtcpka-idleX XX
srvtcpka-intvlX XX
stats admin XXX
stats authXXXX
stats enableXXXX
stats hide-versionXXXX
stats http-request XXX
stats realmXXXX
stats refreshXXXX
stats scopeXXXX
stats show-descXXXX
stats show-legendsXXXX
keyworddefaultsfrontendlistenbackend
stats show-nodeXXXX
stats uriXXXX
stick match  XX
stick on  XX
stick store-request  XX
stick store-response  XX
stick-table XXX
tcp-check commentX XX
tcp-check connectX XX
tcp-check expectX XX
tcp-check sendX XX
tcp-check send-lfX XX
tcp-check send-binaryX XX
tcp-check send-binary-lfX XX
tcp-check set-varX XX
tcp-check unset-varX XX
tcp-request connectionX (!)XX 
tcp-request contentX (!)XXX
tcp-request inspect-delayX (!)XXX
tcp-request sessionX (!)XX 
keyworddefaultsfrontendlistenbackend
tcp-response contentX (!) XX
tcp-response inspect-delayX (!) XX
timeout checkX XX
timeout clientXXX 
timeout client-finXXX 
timeout client-hsXXX 
timeout connectX XX
timeout http-keep-aliveXXXX
timeout http-requestXXXX
timeout queueX XX
timeout serverX XX
timeout server-finX XX
timeout tarpitXXXX
timeout tunnelX XX
(deprecated)transparentX XX
unique-id-formatXXX 
unique-id-headerXXX 
use_backend XX 
use-fcgi-app  XX
use-server  XX

4.2. Alphabetically sorted keywords reference

This section provides a description of each keyword and its usage.
acl <aclname> <criterion> [flags] [operator] <value> ...
Declare or complete an access list.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes(!)
yes(!)
yes
yes
yes
yes
yes
yes
This directive is only available from named defaults sections, not anonymous
ones. ACLs defined in a defaults section are not visible from other sections
using it.
Example:
acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
acl invalid_src  src_port     0:1023
acl local_dst    hdr(host) -i localhost
See section 7 about ACL usage.
backlog <conns>
Give hints to the system about the approximate listen backlog desired size

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<conns>   is the number of pending connections. Depending on the operating
          system, it may represent the number of already acknowledged
          connections, of non-acknowledged ones, or both.
This option is only meaningful for stream listeners, including QUIC ones. Its
behavior however is not identical with QUIC instances.

For all listeners but QUIC, in order to protect against SYN flood attacks,
one solution is to increase the system's SYN backlog size. Depending on the
system, sometimes it is just tunable via a system parameter, sometimes it is
not adjustable at all, and sometimes the system relies on hints given by the
application at the time of the listen() syscall. By default, HAProxy passes
the frontend's maxconn value to the listen() syscall. On systems which can
make use of this value, it can sometimes be useful to be able to specify a
different value, hence this backlog parameter.

On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is
used as a hint and the system accepts up to the smallest greater power of
two, and never more than some limits (usually 32768).

For QUIC listeners, backlog sets a shared limits for both the maximum count
of active handshakes and connections waiting to be accepted. The handshake
phase relies primarily of the network latency with the remote peer, whereas
the second phase depends solely on haproxy load. When either one of this
limit is reached, haproxy starts to drop reception of INITIAL packets,
preventing any new connection allocation, until the connection excess starts
to decrease. This situation may cause browsers to silently downgrade the HTTP
versions and switching to TCP.
balance <algorithm> [ <arguments> ]
balance url_param <param> [check_post]
Define the load balancing algorithm to be used in a backend.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<algorithm> is the algorithm used to select a server when doing load
            balancing. This only applies when no persistence information
            is available, or when a connection is redispatched to another
            server. <algorithm> may be one of the following :

  roundrobin  Each server is used in turns, according to their weights.
              This is the smoothest and fairest algorithm when the server's
              processing time remains equally distributed. This algorithm
              is dynamic, which means that server weights may be adjusted
              on the fly for slow starts for instance. It is limited by
              design to 4095 active servers per backend. Note that in some
              large farms, when a server becomes up after having been down
              for a very short time, it may sometimes take a few hundreds
              requests for it to be re-integrated into the farm and start
              receiving traffic. This is normal, though very rare. It is
              indicated here in case you would have the chance to observe
              it, so that you don't worry. Note: weights are ignored for
              backends in LOG mode.

  static-rr   Each server is used in turns, according to their weights.
              This algorithm is as similar to roundrobin except that it is
              static, which means that changing a server's weight on the
              fly will have no effect. On the other hand, it has no design
              limitation on the number of servers, and when a server goes
              up, it is always immediately reintroduced into the farm, once
              the full map is recomputed. It also uses slightly less CPU to
              run (around -1%). This algorithm is not usable in LOG mode.

  leastconn   The server with the lowest number of connections receives the
              connection. Round-robin is performed within groups of servers
              of the same load to ensure that all servers will be used. Use
              of this algorithm is recommended where very long sessions are
              expected, such as LDAP, SQL, TSE, etc... but is not very well
              suited for protocols using short sessions such as HTTP. This
              algorithm is dynamic, which means that server weights may be
              adjusted on the fly for slow starts for instance. It will
              also consider the number of queued connections in addition to
              the established ones in order to minimize queuing. This
              algorithm is not usable in LOG mode.

  first       The first server with available connection slots receives the
              connection. The servers are chosen from the lowest numeric
              identifier to the highest (see server parameter "id"), which
              defaults to the server's position in the farm. Once a server
              reaches its maxconn value, the next server is used. It does
              not make sense to use this algorithm without setting maxconn.
              The purpose of this algorithm is to always use the smallest
              number of servers so that extra servers can be powered off
              during non-intensive hours. This algorithm ignores the server
              weight, and brings more benefit to long session such as RDP
              or IMAP than HTTP, though it can be useful there too. In
              order to use this algorithm efficiently, it is recommended
              that a cloud controller regularly checks server usage to turn
              them off when unused, and regularly checks backend queue to
              turn new servers on when the queue inflates. Alternatively,
              using "http-check send-state" may inform servers on the load.

  hash        Takes a regular sample expression in argument. The expression
              is evaluated for each request and hashed according to the
              configured hash-type. The result of the hash is divided by
              the total weight of the running servers to designate which
              server will receive the request. This can be used in place of
              "source", "uri", "hdr()", "url_param()", "rdp-cookie" to make
              use of a converter, refine the evaluation, or be used to
              extract data from local variables for example. When the data
              is not available, round robin will apply. This algorithm is
              static by default, which means that changing a server's
              weight on the fly will have no effect, but this can be
              changed using "hash-type". This algorithm is not usable for
              backends in LOG mode, please use "log-hash" instead.

  source      The source IP address is hashed and divided by the total
              weight of the running servers to designate which server will
              receive the request. This ensures that the same client IP
              address will always reach the same server as long as no
              server goes down or up. If the hash result changes due to the
              number of running servers changing, many clients will be
              directed to a different server. This algorithm is generally
              used in TCP mode where no cookie may be inserted. It may also
              be used on the Internet to provide a best-effort stickiness
              to clients which refuse session cookies. This algorithm is
              static by default, which means that changing a server's
              weight on the fly will have no effect, but this can be
              changed using "hash-type". See also the "hash" option above.
              This algorithm is not usable for backends in LOG mode.

  uri         This algorithm hashes either the left part of the URI (before
              the question mark) or the whole URI (if the "whole" parameter
              is present) and divides the hash value by the total weight of
              the running servers. The result designates which server will
              receive the request. This ensures that the same URI will
              always be directed to the same server as long as no server
              goes up or down. This is used with proxy caches and
              anti-virus proxies in order to maximize the cache hit rate.
              Note that this algorithm may only be used in an HTTP backend.
              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type".

              This algorithm supports two optional parameters "len" and
              "depth", both followed by a positive integer number. These
              options may be helpful when it is needed to balance servers
              based on the beginning of the URI only. The "len" parameter
              indicates that the algorithm should only consider that many
              characters at the beginning of the URI to compute the hash.
              Note that having "len" set to 1 rarely makes sense since most
              URIs start with a leading "/".

              The "depth" parameter indicates the maximum directory depth
              to be used to compute the hash. One level is counted for each
              slash in the request. If both parameters are specified, the
              evaluation stops when either is reached.

              A "path-only" parameter indicates that the hashing key starts
              at the first '/' of the path. This can be used to ignore the
              authority part of absolute URIs, and to make sure that HTTP/1
              and HTTP/2 URIs will provide the same hash. See also the
              "hash" option above.

  url_param   The URL parameter specified in argument will be looked up in
              the query string of each HTTP GET request.

              If the modifier "check_post" is used, then an HTTP POST
              request entity will be searched for the parameter argument,
              when it is not found in a query string after a question mark
              ('?') in the URL. The message body will only start to be
              analyzed once either the advertised amount of data has been
              received or the request buffer is full. In the unlikely event
              that chunked encoding is used, only the first chunk is
              scanned. Parameter values separated by a chunk boundary, may
              be randomly balanced if at all. This keyword used to support
              an optional <max_wait> parameter which is now ignored.

              If the parameter is found followed by an equal sign ('=') and
              a value, then the value is hashed and divided by the total
              weight of the running servers. The result designates which
              server will receive the request.

              This is used to track user identifiers in requests and ensure
              that a same user ID will always be sent to the same server as
              long as no server goes up or down. If no value is found or if
              the parameter is not found, then a round robin algorithm is
              applied. Note that this algorithm may only be used in an HTTP
              backend. This algorithm is static by default, which means
              that changing a server's weight on the fly will have no
              effect, but this can be changed using "hash-type". See also
              the "hash" option above.

  hdr(<name>) The HTTP header <name> will be looked up in each HTTP
              request. Just as with the equivalent ACL 'hdr()' function,
              the header name in parenthesis is not case sensitive. If the
              header is absent or if it does not contain any value, the
              roundrobin algorithm is applied instead.

              An optional 'use_domain_only' parameter is available, for
              reducing the hash algorithm to the main domain part with some
              specific headers such as 'Host'. For instance, in the Host
              value "haproxy.1wt.eu", only "1wt" will be considered.

              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type". See also the
              "hash" option above.

  random
  random(<draws>)
              A random number will be used as the key for the consistent
              hashing function. This means that the servers' weights are
              respected, dynamic weight changes immediately take effect, as
              well as new server additions. Random load balancing can be
              useful with large farms or when servers are frequently added
              or removed as it may avoid the hammering effect that could
              result from roundrobin or leastconn in this situation. The
              hash-balance-factor directive can be used to further improve
              fairness of the load balancing, especially in situations
              where servers show highly variable response times. When an
              argument <draws> is present, it must be an integer value one
              or greater, indicating the number of draws before selecting
              the least loaded of these servers. It was indeed demonstrated
              that picking the least loaded of two servers is enough to
              significantly improve the fairness of the algorithm, by
              always avoiding to pick the most loaded server within a farm
              and getting rid of any bias that could be induced by the
              unfair distribution of the consistent list. Higher values N
              will take away N-1 of the highest loaded servers at the
              expense of performance. With very high values, the algorithm
              will converge towards the leastconn's result but much slower.
              The default value is 2, which generally shows very good
              distribution and performance. This algorithm is also known as
              the Power of Two Random Choices and is described here :
              http://www.eecs.harvard.edu/~michaelm/postscripts/handbook2001.pdf

              For backends in LOG mode, the number of draws is ignored and
              a single random is picked since there is no notion of server
              load. Random log balancing can be useful with large farms or
              when servers are frequently added or removed from the pool of
              available servers as it may avoid the hammering effect that
              could result from roundrobin in this situation.

  rdp-cookie
  rdp-cookie(<name>)
              The RDP cookie <name> (or "mstshash" if omitted) will be
              looked up and hashed for each incoming TCP request. Just as
              with the equivalent ACL 'req.rdp_cookie()' function, the name
              is not case-sensitive. This mechanism is useful as a degraded
              persistence mode, as it makes it possible to always send the
              same user (or the same session ID) to the same server. If the
              cookie is not found, the normal roundrobin algorithm is
              used instead.

              Note that for this to work, the frontend must ensure that an
              RDP cookie is already present in the request buffer. For this
              you must use 'tcp-request content accept' rule combined with
              a 'req.rdp_cookie_cnt' ACL.

              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type". See also the
              "hash" option above.

  log-hash    Takes a comma-delimited list of converters in argument. These
              converters are applied in sequence to the input log message,
              and the result will be cast as a string then hashed according
              to the configured hash-type. The resulting hash will be used
              to select the destination server among the ones declared in
              the log backend. The goal of this algorithm is to be able to
              extract a key within the final log message using string
              converters and then be able to stick to the same server thanks
              to the hash. Only "map-based" hashes are supported for now.
              This algorithm is only usable for backends in LOG mode, for
              others, please use "hash" instead.

  sticky      Tries to stick to the same server as much as possible. The
              first server in the list of available servers receives all
              the log messages. When the server goes DOWN, the next server
              in the list takes its place. When a previously DOWN server
              goes back UP it is added at the end of the list so that the
              sticky server doesn't change until it becomes DOWN. This
              algorithm is only usable for backends in LOG mode.

<arguments> is an optional list of arguments which may be needed by some
            algorithms. Right now, only "url_param", "uri" and "log-hash"
            support an optional argument.
The load balancing algorithm of a backend is set to roundrobin when no other
algorithm, mode nor option have been set. The algorithm may only be set once
for each backend. In backends in LOG mode, server "weight" is always ignored.

With authentication schemes that require the same connection like NTLM, URI
based algorithms must not be used, as they would cause subsequent requests
to be routed to different backend servers, breaking the invalid assumptions
NTLM relies on.

TCP/HTTP Examples :
      balance roundrobin
      balance url_param userid
      balance url_param session_id check_post 64
      balance hdr(User-Agent)
      balance hdr(host)
      balance hdr(Host) use_domain_only
      balance hash req.cookie(clientid)
      balance hash var(req.client_id)
      balance hash req.hdr_ip(x-forwarded-for,-1),ipmask(24)

LOG backend examples:
      global
        log backend@mylog-rrb local0 # send all logs to mylog-rrb backend
        log backend@mylog-hash local0 # send all logs to mylog-hash backend

      backend mylog-rrb
        mode log
        balance roundrobin

        server s1 udp@127.0.0.1:514 # will receive 50% of log messages
        server s2 udp@127.0.0.1:514

      backend mylog-hash
        mode log

        # extract "METHOD URL PROTO" at the end of the log message,
        # and let haproxy hash it so that log messages generated from
        # similar requests get sent to the same syslog server:
        balance log-hash 'field(-2,\")'

        # server list here
        server s1 127.0.0.1:514
        #...

Note: the following caveats and limitations on using the "check_post"
extension with "url_param" must be considered :

  - all POST requests are eligible for consideration, because there is no way
    to determine if the parameters will be found in the body or entity which
    may contain binary data. Therefore another method may be required to
    restrict consideration of POST requests that have no URL parameters in
    the body. (see acl http_end)

  - using a <max_wait> value larger than the request buffer size does not
    make sense and is useless. The buffer size is set at build time, and
    defaults to 16 kB.

  - Content-Encoding is not supported, the parameter search will probably
    fail; and load balancing will fall back to Round Robin.

  - Expect: 100-continue is not supported, load balancing will fall back to
    Round Robin.

  - Transfer-Encoding (RFC7230 3.3.1) is only supported in the first chunk.
    If the entire parameter value is not present in the first chunk, the
    selection of server is undefined (actually, defined by how little
    actually appeared in the first chunk).

  - This feature does not support generation of a 100, 411 or 501 response.

  - In some cases, requesting "check_post" MAY attempt to scan the entire
    contents of a message body. Scanning normally terminates when linear
    white space or control characters are found, indicating the end of what
    might be a URL parameter list. This is probably not a concern with SGML
    type message bodies.
bind [<address>]:<port_range> [, ...] [param*]
bind /<path> [, ...] [param*]
Define one or several listening addresses and/or ports in a frontend.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments :
<address>     is optional and can be a host name, an IPv4 address, an IPv6
              address, or '*'. It designates the address the frontend will
              listen on. If unset, all IPv4 addresses of the system will be
              listened on. The same will apply for '*' or the system's
              special address "0.0.0.0". The IPv6 equivalent is '::'. Note
              that for UDP, specific OS features are required when binding
              on multiple addresses to ensure the correct network interface
              and source address will be used on response. In other way,
              for QUIC listeners only bind on multiple addresses if running
              with a modern enough systems.

              Optionally, an address family prefix may be used before the
              address to force the family regardless of the address format,
              which can be useful to specify a path to a unix socket with
              no slash ('/'). Currently supported prefixes are :
                - 'ipv4@'  -> address is always IPv4
                - 'ipv6@'  -> address is always IPv6
                - 'udp@'   -> address is resolved as IPv4 or IPv6 and
                  protocol UDP is used. Currently those listeners are
                  supported only in log-forward sections.
                - 'udp4@'  -> address is always IPv4 and protocol UDP
                  is used. Currently those listeners are supported
                  only in log-forward sections.
                - 'udp6@'  -> address is always IPv6 and protocol UDP
                  is used. Currently those listeners are supported
                  only in log-forward sections.
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only).
                - 'fd@<n>' -> use file descriptor <n> inherited from the
                  parent. The fd must be bound and may or may not already
                  be listening.
                - 'sockpair@<n>'-> like fd@ but you must use the fd of a
                  connected unix socket or of a socketpair. The bind waits
                  to receive a FD over the unix socket and uses it as if it
                  was the FD of an accept(). Should be used carefully.
                - 'quic4@' -> address is resolved as IPv4 and protocol UDP
                  is used. Note that to achieve the best performance with a
                  large traffic you should keep "tune.quic.socket-owner" on
                  connection. Else QUIC connections will be multiplexed
                  over the listener socket. Another alternative would be to
                  duplicate QUIC listener instances over several threads,
                  for example using "shards" keyword to at least reduce
                  thread contention.
                - 'quic6@' -> address is resolved as IPv6 and protocol UDP
                  is used. The performance note for QUIC over IPv4 applies
                  as well.
                - 'rhttp@' [ EXPERIMENTAL ] -> used for reverse HTTP.
                  Address must be a server with the format
                  '<backend>/<server>'. The server will be used to
                  instantiate connections to a remote address. The listener
                  will try to maintain "nbconn" connections. This is an
                  experimental features which requires
                  "expose-experimental-directives" on a line before this
                  bind.

              You may want to reference some environment variables in the
              address parameter, see section 2.3 about environment
              variables.

<port_range>  is either a unique TCP port, or a port range for which the
              proxy will accept connections for the IP address specified
              above. The port is mandatory for TCP listeners. Note that in
              the case of an IPv6 address, the port is always the number
              after the last colon (':'). A range can either be :
               - a numerical port (ex: '80')
               - a dash-delimited ports range explicitly stating the lower
                 and upper bounds (ex: '2000-2100') which are included in
                 the range.

              Particular care must be taken against port ranges, because
              every <address:port> couple consumes one socket (= a file
              descriptor), so it's easy to consume lots of descriptors
              with a simple range, and to run out of sockets. Also, each
              <address:port> couple must be used only once among all
              instances running on a same system. Please note that binding
              to ports lower than 1024 generally require particular
              privileges to start the program, which are independent of
              the 'uid' parameter.

<path>        is a UNIX socket path beginning with a slash ('/'). This is
              alternative to the TCP listening port. HAProxy will then
              receive UNIX connections on the socket located at this place.
              The path must begin with a slash and by default is absolute.
              It can be relative to the prefix defined by "unix-bind" in
              the global section. Note that the total length of the prefix
              followed by the socket path cannot exceed some system limits
              for UNIX sockets, which commonly are set to 107 characters.

<param*>      is a list of parameters common to all sockets declared on the
              same line. These numerous parameters depend on OS and build
              options and have a complete section dedicated to them. Please
              refer to section 5 to for more details.
It is possible to specify a list of address:port combinations delimited by
commas. The frontend will then listen on all of these addresses. There is no
fixed limit to the number of addresses and ports which can be listened on in
a frontend, as well as there is no limit to the number of "bind" statements
in a frontend.
Example :
listen http_proxy
    bind :80,:443
    bind 10.0.0.1:10080,10.0.0.1:10443
    bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy

listen http_https_proxy
    bind :80
    bind :443 ssl crt /etc/haproxy/site.pem

listen http_https_proxy_explicit
    bind ipv6@:80
    bind ipv4@public_ssl:443 ssl crt /etc/haproxy/site.pem
    bind unix@ssl-frontend.sock user root mode 600 accept-proxy

listen external_bind_app1
    bind "fd@${FD_APP1}"

listen h3_quic_proxy
    bind quic4@10.0.0.1:8888 ssl crt /etc/mycrt
Note: regarding Linux's abstract namespace sockets, HAProxy uses the whole
      sun_path length is used for the address length. Some other programs
      such as socat use the string length only by default. Pass the option
      ",unix-tightsocklen=0" to any abstract socket definition in socat to
      make it compatible with HAProxy's.
capture cookie <name> len <length>
Capture and log a cookie in the request and in the response.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments :
<name>    is the beginning of the name of the cookie to capture. In order
          to match the exact name, simply suffix the name with an equal
          sign ('='). The full name will appear in the logs, which is
          useful with application servers which adjust both the cookie name
          and value (e.g. ASPSESSIONXXX).

<length>  is the maximum number of characters to report in the logs, which
          include the cookie name, the equal sign and the value, all in the
          standard "name=value" form. The string will be truncated on the
          right if it exceeds <length>.
Only the first cookie is captured. Both the "cookie" request headers and the
"set-cookie" response headers are monitored. This is particularly useful to
check for application bugs causing session crossing or stealing between
users, because generally the user's cookies can only change on a login page.

When the cookie was not presented by the client, the associated log column
will report "-". When a request does not cause a cookie to be assigned by the
server, a "-" is reported in the response column.

The capture is performed in the frontend only because it is necessary that
the log format does not change for a given frontend depending on the
backends. This may change in the future. Note that there can be only one
"capture cookie" statement in a frontend. The maximum capture length is set
by the global "tune.http.cookielen" setting and defaults to 63 characters. It
is not possible to specify a capture in a "defaults" section.
Example:
capture cookie ASPSESSION len 32
capture request header <name> len <length>
Capture and log the last occurrence of the specified request header.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments :
<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the requests, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.

<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.
The complete value of the last occurrence of the header is captured. The
value will be added to the logs between braces ('{}'). If multiple headers
are captured, they will be delimited by a vertical bar ('|') and will appear
in the same order they were declared in the configuration. Non-existent
headers will be logged just as an empty string. Common uses for request
header captures include the "Host" field in virtual hosting environments, the
"Content-length" when uploads are supported, "User-agent" to quickly
differentiate between real users and robots, and "X-Forwarded-For" in proxied
environments to find where the request came from.

Note that when capturing headers such as "User-agent", some spaces may be
logged, making the log analysis more difficult. Thus be careful about what
you log if you know your log parser is not smart enough to rely on the
braces.

There is no limit to the number of captured request headers nor to their
length, though it is wise to keep them low to limit memory usage per stream.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.
Example:
capture request header Host len 15
capture request header X-Forwarded-For len 15
capture request header Referer len 15
capture response header <name> len <length>
Capture and log the last occurrence of the specified response header.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments :
<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the response, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.

<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.
The complete value of the last occurrence of the header is captured. The
result will be added to the logs between braces ('{}') after the captured
request headers. If multiple headers are captured, they will be delimited by
a vertical bar ('|') and will appear in the same order they were declared in
the configuration. Non-existent headers will be logged just as an empty
string. Common uses for response header captures include the "Content-length"
header which indicates how many bytes are expected to be returned, the
"Location" header to track redirections.

There is no limit to the number of captured response headers nor to their
length, though it is wise to keep them low to limit memory usage per stream.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.
Example:
capture response header Content-length len 9
capture response header Location len 15
clitcpka-cnt <count>
Sets the maximum number of keepalive probes TCP should send before dropping
the connection on the client side.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<count>   is the maximum number of keepalive probes.
This keyword corresponds to the socket option TCP_KEEPCNT. If this keyword
is not specified, system-wide TCP parameter (tcp_keepalive_probes) is used.
The availability of this setting depends on the operating system. It is
known to work on Linux.
clitcpka-idle <timeout>
Sets the time the connection needs to remain idle before TCP starts sending
keepalive probes, if enabled the sending of TCP keepalive packets on the
client side.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<timeout> is the time the connection needs to remain idle before TCP starts
          sending keepalive probes. It is specified in seconds by default,
          but can be in any other unit if the number is suffixed by the
          unit, as explained at the top of this document.
This keyword corresponds to the socket option TCP_KEEPIDLE. If this keyword
is not specified, system-wide TCP parameter (tcp_keepalive_time) is used.
The availability of this setting depends on the operating system. It is
known to work on Linux.
clitcpka-intvl <timeout>
Sets the time between individual keepalive probes on the client side.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<timeout> is the time between individual keepalive probes. It is specified
          in seconds by default, but can be in any other unit if the number
          is suffixed by the unit, as explained at the top of this
          document.
This keyword corresponds to the socket option TCP_KEEPINTVL. If this keyword
is not specified, system-wide TCP parameter (tcp_keepalive_intvl) is used.
The availability of this setting depends on the operating system. It is
known to work on Linux.
compression algo <algorithm> ...
compression type <mime type> ...
Enable HTTP compression.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
algo     is followed by the list of supported compression algorithms for
         responses (legacy keyword)
algo-req is followed by compression algorithm for request (only one is
         provided).
algo-res is followed by the list of supported compression algorithms for
         responses.
type     is followed by the list of MIME types that will be compressed for
         responses (legacy keyword).
type-req is followed by the list of MIME types that will be compressed for
         requests.
type-res is followed by the list of MIME types that will be compressed for
         responses.
The currently supported algorithms are :
  identity     this is mostly for debugging, and it was useful for developing
               the compression feature. Identity does not apply any change on
               data.

  gzip         applies gzip compression. This setting is only available when
               support for zlib or libslz was built in.

  deflate      same as "gzip", but with deflate algorithm and zlib format.
               Note that this algorithm has ambiguous support on many
               browsers and no support at all from recent ones. It is
               strongly recommended not to use it for anything else than
               experimentation. This setting is only available when support
               for zlib or libslz was built in.

  raw-deflate  same as "deflate" without the zlib wrapper, and used as an
               alternative when the browser wants "deflate". All major
               browsers understand it and despite violating the standards,
               it is known to work better than "deflate", at least on MSIE
               and some versions of Safari. Do not use it in conjunction
               with "deflate", use either one or the other since both react
               to the same Accept-Encoding token. This setting is only
               available when support for zlib or libslz was built in.

Compression will be activated depending on the Accept-Encoding request
header. With identity, it does not take care of that header.
If backend servers support HTTP compression, these directives
will be no-op: HAProxy will see the compressed response and will not
compress again. If backend servers do not support HTTP compression and
there is Accept-Encoding header in request, HAProxy will compress the
matching response.

Compression is disabled when:
  * the request does not advertise a supported compression algorithm in the
    "Accept-Encoding" header
  * the response message is not HTTP/1.1 or above
  * HTTP status code is not one of 200, 201, 202, or 203
  * response contain neither a "Content-Length" header nor a
    "Transfer-Encoding" whose last value is "chunked"
  * response contains a "Content-Type" header whose first value starts with
    "multipart"
  * the response contains the "no-transform" value in the "Cache-control"
    header
  * User-Agent matches "Mozilla/4" unless it is MSIE 6 with XP SP2, or MSIE 7
    and later
  * The response contains a "Content-Encoding" header, indicating that the
    response is already compressed (see compression offload)
  * The response contains an invalid "ETag" header or multiple ETag headers

Note: The compression does not emit the Warning header.
Examples :
compression algo gzip
compression type text/html text/plain
Makes HAProxy work as a compression offloader only.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
yes
yes
The "offload" setting makes HAProxy remove the Accept-Encoding header to
prevent backend servers from compressing responses. It is strongly
recommended not to do this because this means that all the compression work
will be done on the single point where HAProxy is located. However in some
deployment scenarios, HAProxy may be installed in front of a buggy gateway
with broken HTTP compression implementation which can't be turned off.
In that case HAProxy can be used to prevent that gateway from emitting
invalid payloads. In this case, simply removing the header in the
configuration does not work because it applies before the header is parsed,
so that prevents HAProxy from compressing. The "offload" setting should
then be used for such scenarios.

If this setting is used in a defaults section, a warning is emitted and the
option is ignored.
Makes haproxy able to compress both requests and responses.
Valid values are "request", to compress only requests, "response", to
compress only responses, or "both", when you want to compress both.
The default value is "response".

May be used in the following contexts: http
cookie <name> [ rewrite | insert | prefix ] [ indirect ] [ nocache ] [ postonly ] [ preserve ] [ httponly ] [ secure ] [ domain <domain> ]* [ maxidle <idle> ] [ maxlife <life> ] [ dynamic ] [ attr <value> ]*
Enable cookie-based persistence in a backend.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<name>    is the name of the cookie which will be monitored, modified or
          inserted in order to bring persistence. This cookie is sent to
          the client via a "Set-Cookie" header in the response, and is
          brought back by the client in a "Cookie" header in all requests.
          Special care should be taken to choose a name which does not
          conflict with any likely application cookie. Also, if the same
          backends are subject to be used by the same clients (e.g.
          HTTP/HTTPS), care should be taken to use different cookie names
          between all backends if persistence between them is not desired.

rewrite   This keyword indicates that the cookie will be provided by the
          server and that HAProxy will have to modify its value to set the
          server's identifier in it. This mode is handy when the management
          of complex combinations of "Set-cookie" and "Cache-control"
          headers is left to the application. The application can then
          decide whether or not it is appropriate to emit a persistence
          cookie. Since all responses should be monitored, this mode
          doesn't work in HTTP tunnel mode. Unless the application
          behavior is very complex and/or broken, it is advised not to
          start with this mode for new deployments. This keyword is
          incompatible with "insert" and "prefix".

insert    This keyword indicates that the persistence cookie will have to
          be inserted by HAProxy in server responses if the client did not

          already have a cookie that would have permitted it to access this
          server. When used without the "preserve" option, if the server
          emits a cookie with the same name, it will be removed before
          processing. For this reason, this mode can be used to upgrade
          existing configurations running in the "rewrite" mode. The cookie
          will only be a session cookie and will not be stored on the
          client's disk. By default, unless the "indirect" option is added,
          the server will see the cookies emitted by the client. Due to
          caching effects, it is generally wise to add the "nocache" or
          "postonly" keywords (see below). The "insert" keyword is not
          compatible with "rewrite" and "prefix".

prefix    This keyword indicates that instead of relying on a dedicated
          cookie for the persistence, an existing one will be completed.
          This may be needed in some specific environments where the client
          does not support more than one single cookie and the application
          already needs it. In this case, whenever the server sets a cookie
          named <name>, it will be prefixed with the server's identifier
          and a delimiter. The prefix will be removed from all client
          requests so that the server still finds the cookie it emitted.
          Since all requests and responses are subject to being modified,
          this mode doesn't work with tunnel mode. The "prefix" keyword is
          not compatible with "rewrite" and "insert". Note: it is highly
          recommended not to use "indirect" with "prefix", otherwise server
          cookie updates would not be sent to clients.

indirect  When this option is specified, no cookie will be emitted to a
          client which already has a valid one for the server which has
          processed the request. If the server sets such a cookie itself,
          it will be removed, unless the "preserve" option is also set. In
          "insert" mode, this will additionally remove cookies from the
          requests transmitted to the server, making the persistence
          mechanism totally transparent from an application point of view.
          Note: it is highly recommended not to use "indirect" with
          "prefix", otherwise server cookie updates would not be sent to
          clients.

nocache   This option is recommended in conjunction with the insert mode
          when there is a cache between the client and HAProxy, as it
          ensures that a cacheable response will be tagged non-cacheable if
          a cookie needs to be inserted. This is important because if all
          persistence cookies are added on a cacheable home page for
          instance, then all customers will then fetch the page from an
          outer cache and will all share the same persistence cookie,
          leading to one server receiving much more traffic than others.
          See also the "insert" and "postonly" options.

postonly  This option ensures that cookie insertion will only be performed
          on responses to POST requests. It is an alternative to the
          "nocache" option, because POST responses are not cacheable, so
          this ensures that the persistence cookie will never get cached.
          Since most sites do not need any sort of persistence before the
          first POST which generally is a login request, this is a very
          efficient method to optimize caching without risking to find a
          persistence cookie in the cache.
          See also the "insert" and "nocache" options.

preserve  This option may only be used with "insert" and/or "indirect". It
          allows the server to emit the persistence cookie itself. In this
          case, if a cookie is found in the response, HAProxy will leave it
          untouched. This is useful in order to end persistence after a
          logout request for instance. For this, the server just has to
          emit a cookie with an invalid value (e.g. empty) or with a date in
          the past. By combining this mechanism with the "disable-on-404"
          check option, it is possible to perform a completely graceful
          shutdown because users will definitely leave the server after
          they logout.

httponly  This option tells HAProxy to add an "HttpOnly" cookie attribute
          when a cookie is inserted. This attribute is used so that a
          user agent doesn't share the cookie with non-HTTP components.
          Please check RFC6265 for more information on this attribute.

secure    This option tells HAProxy to add a "Secure" cookie attribute when
          a cookie is inserted. This attribute is used so that a user agent
          never emits this cookie over non-secure channels, which means
          that a cookie learned with this flag will be presented only over
          SSL/TLS connections. Please check RFC6265 for more information on
          this attribute.

domain    This option allows to specify the domain at which a cookie is
          inserted. It requires exactly one parameter: a valid domain
          name. If the domain begins with a dot, the browser is allowed to
          use it for any host ending with that name. It is also possible to
          specify several domain names by invoking this option multiple
          times. Some browsers might have small limits on the number of
          domains, so be careful when doing that. For the record, sending
          10 domains to MSIE 6 or Firefox 2 works as expected.

maxidle   This option allows inserted cookies to be ignored after some idle
          time. It only works with insert-mode cookies. When a cookie is
          sent to the client, the date this cookie was emitted is sent too.
          Upon further presentations of this cookie, if the date is older
          than the delay indicated by the parameter (in seconds), it will
          be ignored. Otherwise, it will be refreshed if needed when the
          response is sent to the client. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). When
          this option is set and a cookie has no date, it is always
          accepted, but gets refreshed in the response. This maintains the
          ability for admins to access their sites. Cookies that have a
          date in the future further than 24 hours are ignored. Doing so
          lets admins fix timezone issues without risking kicking users off
          the site.

maxlife   This option allows inserted cookies to be ignored after some life
          time, whether they're in use or not. It only works with insert
          mode cookies. When a cookie is first sent to the client, the date
          this cookie was emitted is sent too. Upon further presentations
          of this cookie, if the date is older than the delay indicated by
          the parameter (in seconds), it will be ignored. If the cookie in
          the request has no date, it is accepted and a date will be set.
          Cookies that have a date in the future further than 24 hours are
          ignored. Doing so lets admins fix timezone issues without risking
          kicking users off the site. Contrary to maxidle, this value is
          not refreshed, only the first visit date counts. Both maxidle and
          maxlife may be used at the time. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). This
          is stronger than the maxidle method in that it forces a
          redispatch after some absolute delay.

dynamic   Activate dynamic cookies. When used, a session cookie is
          dynamically created for each server, based on the IP and port
          of the server, and a secret key, specified in the
          "dynamic-cookie-key" backend directive.
          The cookie will be regenerated each time the IP address change,
          and is only generated for IPv4/IPv6.

attr      This option tells HAProxy to add an extra attribute when a
          cookie is inserted. The attribute value can contain any
          characters except control ones or ";". This option may be
          repeated.
There can be only one persistence cookie per HTTP backend, and it can be
declared in a defaults section. The value of the cookie will be the value
indicated after the "cookie" keyword in a "server" statement. If no cookie
is declared for a given server, the cookie is not set.
Examples :
cookie JSESSIONID prefix
cookie SRV insert indirect nocache
cookie SRV insert postonly indirect
cookie SRV insert indirect nocache maxidle 30m maxlife 8h
declare capture [ request | response ] len <length>
Declares a capture slot.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments:
<length> is the length allowed for the capture.
This declaration is only available in the frontend or listen section, but the
reserved slot can be used in the backends. The "request" keyword allocates a
capture slot for use in the request, and "response" allocates a capture slot
for use in the response.
Change default options for a server in a backend

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments:
<param*>  is a list of parameters for this server. The "default-server"
          keyword accepts an important number of options and has a complete
          section dedicated to it. Please refer to section 5 for more
          details.
Example :
default-server inter 1000 weight 13
default_backend <backend>
Specify the backend to use when no "use_backend" rule has been matched.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<backend> is the name of the backend to use.
When doing content-switching between frontend and backends using the
"use_backend" keyword, it is often useful to indicate which backend will be
used when no rule has matched. It generally is the dynamic backend which
will catch all undetermined requests.
Example :
use_backend     dynamic  if  url_dyn
use_backend     static   if  url_css url_img extension_img
default_backend dynamic
description <string>
Describe a listen, frontend or backend.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
yes
yes
Arguments : string
Allows to add a sentence to describe the related object in the HAProxy HTML
stats page. The description will be printed on the right of the object name
it describes.
No need to backslash spaces in the <string> arguments.
Disable a proxy, frontend or backend.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments : none
The "disabled" keyword is used to disable an instance, mainly in order to
liberate a listening port or to temporarily disable a service. The instance
will still be created and its configuration will be checked, but it will be
created in the "stopped" state and will appear as such in the statistics. It
will not receive any traffic nor will it send any health-checks or logs. It
is possible to disable many instances at once by adding the "disabled"
keyword in a "defaults" section.
dispatch <address>:<port>
Set a default server address

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
no
no
yes
yes
yes
yes
Arguments :
<address> is the IPv4 address of the default server. Alternatively, a
          resolvable hostname is supported, but this name will be resolved
          during start-up.

<ports>   is a mandatory port specification. All connections will be sent
          to this port, and it is not permitted to use port offsets as is
          possible with normal servers.
The "dispatch" keyword designates a default server for use when no other
server can take the connection. In the past it was used to forward non
persistent connections to an auxiliary load balancer. Due to its simple
syntax, it has also been used for simple TCP relays. It is recommended not to
use it for more clarity, and to use the "server" directive instead.
Set the dynamic cookie secret key for a backend.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : The secret key to be used.
When dynamic cookies are enabled (see the "dynamic" directive for cookie),
a dynamic cookie is created for each server (unless one is explicitly
specified on the "server" line), using a hash of the IP address of the
server, the TCP port, and the secret key.
That way, we can ensure session persistence across multiple load-balancers,
even if servers are dynamically added or removed.
Enable a proxy, frontend or backend.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments : none
The "enabled" keyword is used to explicitly enable an instance, when the
defaults has been set to "disabled". This is very rarely used.
errorfile <code> <file>
Return a file contents instead of errors generated by HAProxy

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 401, 403, 404, 405, 407, 408, 410,
          413, 425, 429, 500, 501, 502, 503, and 504.

<file>    designates a file containing the full HTTP response. It is
          recommended to follow the common practice of appending ".http" to
          the filename so that people do not confuse the response with HTML
          error pages, and to use absolute paths, since files are read
          before any chroot is performed.
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

The files are parsed when HAProxy starts and must be valid according to the
HTTP specification. They should not exceed the configured buffer size
(BUFSIZE), which generally is 16 kB, otherwise an internal error will be
returned. It is also wise not to put any reference to local contents
(e.g. images) in order to avoid loops between the client and HAProxy when all
servers are down, causing an error to be returned instead of an
image. Finally, The response cannot exceed (tune.bufsize - tune.maxrewrite)
so that "http-after-response" rules still have room to operate (see
"tune.maxrewrite").

The files are read at the same time as the configuration and kept in memory.
For this reason, the errors continue to be returned even when the process is
chrooted, and no file change is considered while the process is running. A
simple method for developing those files consists in associating them to the
403 status code and interrogating a blocked URL.
Example :
errorfile 400 /etc/haproxy/errorfiles/400badreq.http
errorfile 408 /dev/null  # work around Chrome pre-connect bug
errorfile 403 /etc/haproxy/errorfiles/403forbid.http
errorfile 503 /etc/haproxy/errorfiles/503sorry.http
errorfiles <name> [<code> ...]
Import, fully or partially, the error files defined in the <name> http-errors
section.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<name>  is the name of an existing http-errors section.

<code>  is a HTTP status code. Several status code may be listed.
        Currently, HAProxy is capable of generating codes 200, 400, 401,
        403, 404, 405, 407, 408, 410, 413, 425, 429, 500, 501, 502, 503,
        and 504.
Errors defined in the http-errors section with the name <name> are imported
in the current proxy. If no status code is specified, all error files of the
http-errors section are imported. Otherwise, only error files associated to
the listed status code are imported. Those error files override the already
defined custom errors for the proxy. And they may be overridden by following
ones. Functionally, it is exactly the same as declaring all error files by
hand using "errorfile" directives.
Example :
errorfiles generic
errorfiles site-1 403 404
errorloc <code> <url>
errorloc302 <code> <url>
Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 401, 403, 404, 405, 407, 408, 410,
          413, 425, 429, 500, 501, 502, 503, and 504.

<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

Note that both keyword return the HTTP 302 status code, which tells the
client to fetch the designated URL using the same HTTP method. This can be
quite problematic in case of non-GET methods such as POST, because the URL
sent to the client might not be allowed for something other than GET. To
work around this problem, please use "errorloc303" which send the HTTP 303
status code, indicating to the client that the URL must be fetched with a GET
request.
errorloc303 <code> <url>
Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 401, 403, 404, 405, 407, 408, 410,
          413, 425, 429, 500, 501, 502, 503, and 504.

<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

Note that both keyword return the HTTP 303 status code, which tells the
client to fetch the designated URL using the same HTTP GET method. This
solves the usual problems associated with "errorloc" and the 302 code. It is
possible that some very old browsers designed before HTTP/1.1 do not support
it, but no such problem has been reported till now.
email-alert from <emailaddr>
Declare the from email address to be used in both the envelope and header
of email alerts. This is the address that email alerts are sent from.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<emailaddr> is the from email address to use when sending email alerts
Also requires "email-alert mailers" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.
Declare the maximum log level of messages for which email alerts will be
sent. This acts as a filter on the sending of email alerts.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<level> One of the 8 syslog levels:
          emerg alert crit err warning notice info  debug
        The above syslog levels are ordered from lowest to highest.
By default level is alert

Also requires "email-alert from", "email-alert mailers" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.

Alerts are sent when :

* An un-paused server is marked as down and <level> is alert or lower
* A paused server is marked as down and <level> is notice or lower
* A server is marked as up or enters the drain state and <level>
  is notice or lower
* "option log-health-checks" is enabled, <level> is info or lower,
   and a health check status update occurs
email-alert mailers <mailersect>
Declare the mailers to be used when sending email alerts

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<mailersect> is the name of the mailers section to send email alerts.
Also requires "email-alert from" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.
Declare the to hostname address to be used when communicating with
mailers.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<hostname> is the hostname to use when communicating with mailers
By default the systems hostname is used.

Also requires "email-alert from", "email-alert mailers" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.
email-alert to <emailaddr>
Declare both the recipient address in the envelope and to address in the
header of email alerts. This is the address that email alerts are sent to.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<emailaddr> is the to email address to use when sending email alerts
Also requires "email-alert mailers" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.
Specifies the log format string to use in case of connection error on the frontend side.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
This directive specifies the log format string that will be used for logs
containing information related to errors, timeouts, retries redispatches or
HTTP status code 5xx. This format will in short be used for every log line
that would be concerned by the "log-separate-errors" option, including
connection errors described in section 8.2.5.

If the directive is used in a defaults section, all subsequent frontends will
use the same log format. Please see section 8.2.4 which covers the log format
string in depth.

"error-log-format" directive overrides previous "error-log-format"
directives.
force-persist { if | unless } <condition>
Declare a condition to force persistence on down servers

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
no
no
yes
yes
yes
yes
By default, requests are not dispatched to down servers. It is possible to
force this using "option persist", but it is unconditional and redispatches
to a valid server if "option redispatch" is set. That leaves with very little
possibilities to force some requests to reach a server which is artificially
marked down for maintenance operations.

The "force-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore the down status of
a server and still try to connect to it. That makes it possible to start a
server, still replying an error to the health checks, and run a specially
configured browser to test the service. Among the handy methods, one could
use a specific source IP address, or a specific cookie. The cookie also has
the advantage that it can easily be added/removed on the browser from a test
page. Once the service is validated, it is then possible to open the service
to the world by returning a valid response to health checks.

The forced persistence is enabled when an "if" condition is met, or unless an
"unless" condition is met. The final redispatch is always disabled when this
is used.
filter <name> [param*]
Add the filter <name> in the filter list attached to the proxy.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
yes
yes
Arguments :
<name>     is the name of the filter. Officially supported filters are
           referenced in section 9.

<param*>   is a list of parameters accepted by the filter <name>. The
           parsing of these parameters are the responsibility of the
           filter. Please refer to the documentation of the corresponding
           filter (section 9) for all details on the supported parameters.
Multiple occurrences of the filter line can be used for the same proxy. The
same filter can be referenced many times if needed.
Example:
listen
  bind *:80

  filter trace name BEFORE-HTTP-COMP
  filter compression
  filter trace name AFTER-HTTP-COMP

  compression algo gzip
  compression offload

  server srv1 192.168.0.1:80
fullconn <conns>
Specify at what backend load the servers will reach their maxconn

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<conns>   is the number of connections on the backend which will make the
          servers use the maximal number of connections.
When a server has a "maxconn" parameter specified, it means that its number
of concurrent connections will never go higher. Additionally, if it has a
"minconn" parameter, it indicates a dynamic limit following the backend's
load. The server will then always accept at least <minconn> connections,
never more than <maxconn>, and the limit will be on the ramp between both
values when the backend has less than <conns> concurrent connections. This
makes it possible to limit the load on the servers during normal loads, but
push it further for important loads without overloading the servers during
exceptional loads.

Since it's hard to get this value right, HAProxy automatically sets it to
10% of the sum of the maxconns of all frontends that may branch to this
backend (based on "use_backend" and "default_backend" rules). That way it's
safe to leave it unset. However, "use_backend" involving dynamic names are
not counted since there is no way to know if they could match or not.
Example :
# The servers will accept between 100 and 1000 concurrent connections each
# and the maximum of 1000 will be reached when the backend reaches 10000
# connections.
backend dynamic
   fullconn   10000
   server     srv1   dyn1:80 minconn 100 maxconn 1000
   server     srv2   dyn2:80 minconn 100 maxconn 1000
Specify the balancing factor for bounded-load consistent hashing

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
no
no
yes
yes
Arguments :
<factor> is the control for the maximum number of concurrent requests to
         send to a server, expressed as a percentage of the average number
         of concurrent requests across all of the active servers.
Specifying a "hash-balance-factor" for a server with "hash-type consistent"
enables an algorithm that prevents any one server from getting too many
requests at once, even if some hash buckets receive many more requests than
others. Setting <factor> to 0 (the default) disables the feature. Otherwise,
<factor> is a percentage greater than 100. For example, if <factor> is 150,
then no server will be allowed to have a load more than 1.5 times the average.
If server weights are used, they will be respected.

If the first-choice server is disqualified, the algorithm will choose another
server based on the request hash, until a server with additional capacity is
found. A higher <factor> allows more imbalance between the servers, while a
lower <factor> means that more servers will be checked on average, affecting
performance. Reasonable values are from 125 to 200.

This setting is also used by "balance random" which internally relies on the
consistent hashing mechanism.
hash-type <method> <function> <modifier>
Specify a method to use for mapping hashes to servers

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<method> is the method used to select a server from the hash computed by
         the <function> :

  map-based   the hash table is a static array containing all alive servers.
              The hashes will be very smooth, will consider weights, but
              will be static in that weight changes while a server is up
              will be ignored. This means that there will be no slow start.
              Also, since a server is selected by its position in the array,
              most mappings are changed when the server count changes. This
              means that when a server goes up or down, or when a server is
              added to a farm, most connections will be redistributed to
              different servers. This can be inconvenient with caches for
              instance.

  consistent  the hash table is a tree filled with many occurrences of each
              server. The hash key is looked up in the tree and the closest
              server is chosen. This hash is dynamic, it supports changing
              weights while the servers are up, so it is compatible with the
              slow start feature. It has the advantage that when a server
              goes up or down, only its associations are moved. When a
              server is added to the farm, only a few part of the mappings
              are redistributed, making it an ideal method for caches.
              However, due to its principle, the distribution will never be
              very smooth and it may sometimes be necessary to adjust a
              server's weight or its ID to get a more balanced distribution.
              In order to get the same distribution on multiple load
              balancers, it is important that all servers have the exact
              same IDs. Note: consistent hash uses sdbm and avalanche if no
              hash function is specified.

<function> is the hash function to be used :

   sdbm   this function was created initially for sdbm (a public-domain
          reimplementation of ndbm) database library. It was found to do
          well in scrambling bits, causing better distribution of the keys
          and fewer splits. It also happens to be a good general hashing
          function with good distribution, unless the total server weight
          is a multiple of 64, in which case applying the avalanche
          modifier may help.

   djb2   this function was first proposed by Dan Bernstein many years ago
          on comp.lang.c. Studies have shown that for certain workload this
          function provides a better distribution than sdbm. It generally
          works well with text-based inputs though it can perform extremely
          poorly with numeric-only input or when the total server weight is
          a multiple of 33, unless the avalanche modifier is also used.

   wt6    this function was designed for HAProxy while testing other
          functions in the past. It is not as smooth as the other ones, but
          is much less sensible to the input data set or to the number of
          servers. It can make sense as an alternative to sdbm+avalanche or
          djb2+avalanche for consistent hashing or when hashing on numeric
          data such as a source IP address or a visitor identifier in a URL
          parameter.

   crc32  this is the most common CRC32 implementation as used in Ethernet,
          gzip, PNG, etc. It is slower than the other ones but may provide
          a better distribution or less predictable results especially when
          used on strings.

   none   don't hash the key, the key will be used as a hash, this can be
          useful to manually hash the key using a converter for that purpose
          and let haproxy use the result directly.

<modifier> indicates an optional method applied after hashing the key :

   avalanche   This directive indicates that the result from the hash
               function above should not be used in its raw form but that
               a 4-byte full avalanche hash must be applied first. The
               purpose of this step is to mix the resulting bits from the
               previous hash in order to avoid any undesired effect when
               the input contains some limited values or when the number of
               servers is a multiple of one of the hash's components (64
               for SDBM, 33 for DJB2). Enabling avalanche tends to make the
               result less predictable, but it's also not as smooth as when
               using the original function. Some testing might be needed
               with some workloads. This hash is one of the many proposed
               by Bob Jenkins.
The default hash type is "map-based" and is recommended for most usages. The
default function is "sdbm", the selection of a function should be based on
the range of the values being hashed.
http-after-response <action> <options...> [ { if | unless } <condition> ]
Access control for all Layer 7 responses (server, applet/service and internal
ones).

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes(!)
yes(!)
yes
yes
yes
yes
yes
yes
The http-after-response statement defines a set of rules which apply to layer
7 processing. The rules are evaluated in their declaration order when they
are met in a frontend, listen or backend section. Since these rules apply on
responses, the backend rules are applied first, followed by the frontend's
rules. Any rule may optionally be followed by an ACL-based condition, in
which case it will only be evaluated if the condition evaluates true.

Unlike http-response rules, these ones are applied on all responses, the
server ones but also to all responses generated by HAProxy. These rules are
evaluated at the end of the responses analysis, before the data forwarding
phase.

The condition is evaluated just before the action is executed, and the action
is performed exactly once. As such, there is no problem if an action changes
an element which is checked as part of the condition. This also means that
multiple actions may rely on the same condition so that the first action that
changes the condition's evaluation is sufficient to implicitly disable the
remaining actions. This is used for example when trying to assign a value to
a variable from various sources when it's empty. There is no limit to the
number of "http-after-response" statements per instance.

The first keyword after "http-after-response" in the syntax is the rule's
action, optionally followed by a varying number of arguments for the action.
The supported actions and their respective syntaxes are enumerated in section
4.3 "Actions" (look for actions which tick "HTTP Aft").

This directive is only available from named defaults sections, not anonymous
ones. Rules defined in the defaults section are evaluated before ones in the
associated proxy section. To avoid ambiguities, in this case the same
defaults section cannot be used by proxies with the frontend capability and
by proxies with the backend capability. It means a listen section cannot use
a defaults section defining such rules.

Note: Errors emitted in early stage of the request parsing are handled by the
      multiplexer at a lower level, before any http analysis. Thus no
      http-after-response ruleset is evaluated on these errors.
Example:
http-after-response set-header Strict-Transport-Security "max-age=31536000"
http-after-response set-header Cache-Control "no-store,no-cache,private"
http-after-response set-header Pragma "no-cache"
Defines a comment for the following the http-check rule, reported in logs if
it fails.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<string>  is the comment message to add in logs if the following http-check
          rule fails.
It only works for connect, send and expect rules. It is useful to make
user-friendly error reporting.
http-check connect [default] [port <expr>] [addr <ip>] [send-proxy] [via-socks4] [ssl] [sni <sni>] [alpn <alpn>] [linger] [proto <name>] [comment <msg>]
Opens a new connection to perform an HTTP health check

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
comment <msg>  defines a message to report if the rule evaluation fails.

default      Use default options of the server line to do the health
             checks. The server options are used only if not redefined.

port <expr>  if not set, check port or server port is used.
             It tells HAProxy where to open the connection to.
             <port> must be a valid TCP port source integer, from 1 to
             65535 or an sample-fetch expression.

addr <ip>    defines the IP address to do the health check.

send-proxy   send a PROXY protocol string

via-socks4   enables outgoing health checks using upstream socks4 proxy.

ssl          opens a ciphered connection

sni <sni>    specifies the SNI to use to do health checks over SSL.

alpn <alpn>  defines which protocols to advertise with ALPN. The protocol
             list consists in a comma-delimited list of protocol names,
             for instance: "h2,http/1.1". If it is not set, the server ALPN
             is used.

proto <name> forces the multiplexer's protocol to use for this connection.
             It must be an HTTP mux protocol and it must be usable on the
             backend side. The list of available protocols is reported in
             haproxy -vv.

linger       cleanly close the connection instead of using a single RST.
Just like tcp-check health checks, it is possible to configure the connection
to use to perform HTTP health check. This directive should also be used to
describe a scenario involving several request/response exchanges, possibly on
different ports or with different servers.

When there are no TCP port configured on the server line neither server port
directive, then the first step of the http-check sequence must be to specify
the port with a "http-check connect".

In an http-check ruleset a 'connect' is required, it is also mandatory to start
the ruleset with a 'connect' rule. Purpose is to ensure admin know what they
do.

When a connect must start the ruleset, if may still be preceded by set-var,
unset-var or comment rules.
Examples :
# check HTTP and HTTPs services on a server.
# first open port 80 thanks to server line port directive, then
# tcp-check opens port 443, ciphered and run a request on it:
option httpchk

http-check connect
http-check send meth GET uri / ver HTTP/1.1 hdr host haproxy.1wt.eu
http-check expect status 200-399
http-check connect port 443 ssl sni haproxy.1wt.eu
http-check send meth GET uri / ver HTTP/1.1 hdr host haproxy.1wt.eu
http-check expect status 200-399

server www 10.0.0.1 check port 80
Enable a maintenance mode upon HTTP/404 response to health-checks

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
When this option is set, a server which returns an HTTP code 404 will be
excluded from further load-balancing, but will still receive persistent
connections. This provides a very convenient method for Web administrators
to perform a graceful shutdown of their servers. It is also important to note
that a server which is detected as failed while it was in this mode will not
generate an alert, just a notice. If the server responds 2xx or 3xx again, it
will immediately be reinserted into the farm. The status on the stats page
reports "NOLB" for a server in this mode. It is important to note that this
option only works in conjunction with the "httpchk" option. If this option
is used with "http-check expect", then it has precedence over it so that 404
responses will still be considered as soft-stop. Note also that a stopped
server will stay stopped even if it replies 404s. This option is only
evaluated for running servers.
http-check expect [min-recv <int>] [comment <msg>] [ok-status <st>] [error-status <st>] [tout-status <st>] [on-success <fmt>] [on-error <fmt>] [status-code <expr>] [!] <match> <pattern>
Make HTTP health checks consider response contents or specific status codes

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
comment <msg>  defines a message to report if the rule evaluation fails.

min-recv  is optional and can define the minimum amount of data required to
          evaluate the current expect rule. If the number of received bytes
          is under this limit, the check will wait for more data. This
          option can be used to resolve some ambiguous matching rules or to
          avoid executing costly regex matches on content known to be still
          incomplete. If an exact string is used, the minimum between the
          string length and this parameter is used. This parameter is
          ignored if it is set to -1. If the expect rule does not match,
          the check will wait for more data. If set to 0, the evaluation
          result is always conclusive.

ok-status <st>     is optional and can be used to set the check status if
                   the expect rule is successfully evaluated and if it is
                   the last rule in the tcp-check ruleset. "L7OK", "L7OKC",
                   "L6OK" and "L4OK" are supported :
                     - L7OK  : check passed on layer 7
                     - L7OKC : check conditionally passed on layer 7, set
                               server to NOLB state.
                     - L6OK  : check passed on layer 6
                     - L4OK  : check passed on layer 4
                   By default "L7OK" is used.

error-status <st>  is optional and can be used to set the check status if
                   an error occurred during the expect rule evaluation.
                   "L7OKC", "L7RSP", "L7STS", "L6RSP" and "L4CON" are
                   supported :
                     - L7OKC : check conditionally passed on layer 7, set
                               server to NOLB state.
                     - L7RSP : layer 7 invalid response - protocol error
                     - L7STS : layer 7 response error, for example HTTP 5xx
                     - L6RSP : layer 6 invalid response - protocol error
                     - L4CON : layer 1-4 connection problem
                   By default "L7RSP" is used.

tout-status <st>   is optional and can be used to set the check status if
                   a timeout occurred during the expect rule evaluation.
                   "L7TOUT", "L6TOUT", and "L4TOUT" are supported :
                     - L7TOUT : layer 7 (HTTP/SMTP) timeout
                     - L6TOUT : layer 6 (SSL) timeout
                     - L4TOUT : layer 1-4 timeout
                   By default "L7TOUT" is used.

on-success <fmt>   is optional and can be used to customize the
                   informational message reported in logs if the expect
                   rule is successfully evaluated and if it is the last rule
                   in the tcp-check ruleset. <fmt> is a log-format string.

on-error <fmt>     is optional and can be used to customize the
                   informational message reported in logs if an error
                   occurred during the expect rule evaluation. <fmt> is a
                   log-format string.

<match>   is a keyword indicating how to look for a specific pattern in the
          response. The keyword may be one of "status", "rstatus", "hdr",
          "fhdr", "string", or "rstring". The keyword may be preceded by an
          exclamation mark ("!") to negate the match. Spaces are allowed
          between the exclamation mark and the keyword. See below for more
          details on the supported keywords.

<pattern> is the pattern to look for. It may be a string, a regular
          expression or a more complex pattern with several arguments. If
          the string pattern contains spaces, they must be escaped with the
          usual backslash ('\').
By default, "option httpchk" considers that response statuses 2xx and 3xx
are valid, and that others are invalid. When "http-check expect" is used,
it defines what is considered valid or invalid. Only one "http-check"
statement is supported in a backend. If a server fails to respond or times
out, the check obviously fails. The available matches are :

  status <codes> :  test the status codes found parsing <codes> string. it
                    must be a comma-separated list of status codes or range
                    codes. A health check response will be considered as
                    valid if the response's status code matches any status
                    code or is inside any range of the list. If the "status"
                    keyword is prefixed with "!", then the response will be
                    considered invalid if the status code matches.

  rstatus <regex> : test a regular expression for the HTTP status code.
                    A health check response will be considered valid if the
                    response's status code matches the expression. If the
                    "rstatus" keyword is prefixed with "!", then the response
                    will be considered invalid if the status code matches.
                    This is mostly used to check for multiple codes.

  hdr  { name | name-lf } [ -m <meth> ] <name>
       [ { value | value-lf } [ -m <meth> ] <value> :
                    test the specified header pattern on the HTTP response
                    headers. The name pattern is mandatory but the value
                    pattern is optional. If not specified, only the header
                    presence is verified. <meth> is the matching method,
                    applied on the header name or the header value. Supported
                    matching methods are "str" (exact match), "beg" (prefix
                    match), "end" (suffix match), "sub" (substring match) or
                    "reg" (regex match). If not specified, exact matching
                    method is used. If the "name-lf" parameter is used,
                    <name> is evaluated as a log-format string. If "value-lf"
                    parameter is used, <value> is evaluated as a log-format
                    string. These parameters cannot be used with the regex
                    matching method. Finally, the header value is considered
                    as comma-separated list. Note that matchings are case
                    insensitive on the header names.

  fhdr { name | name-lf } [ -m <meth> ] <name>
       [ { value | value-lf } [ -m <meth> ] <value> :
                    test the specified full header pattern on the HTTP
                    response headers. It does exactly the same than "hdr"
                    keyword, except the full header value is tested, commas
                    are not considered as delimiters.

  string <string> : test the exact string match in the HTTP response body.
                    A health check response will be considered valid if the
                    response's body contains this exact string. If the
                    "string" keyword is prefixed with "!", then the response
                    will be considered invalid if the body contains this
                    string. This can be used to look for a mandatory word at
                    the end of a dynamic page, or to detect a failure when a
                    specific error appears on the check page (e.g. a stack
                    trace).

  rstring <regex> : test a regular expression on the HTTP response body.
                    A health check response will be considered valid if the
                    response's body matches this expression. If the "rstring"
                    keyword is prefixed with "!", then the response will be
                    considered invalid if the body matches the expression.
                    This can be used to look for a mandatory word at the end
                    of a dynamic page, or to detect a failure when a specific
                    error appears on the check page (e.g. a stack trace).

  string-lf <fmt> : test a log-format string match in the HTTP response body.
                    A health check response will be considered valid if the
                    response's body contains the  string resulting of the
                    evaluation of <fmt>, which follows the log-format rules.
                    If prefixed with "!", then the response will be
                    considered invalid if the body contains the string.

It is important to note that the responses will be limited to a certain size
defined by the global "tune.bufsize" option, which defaults to 16384 bytes.
Thus, too large responses may not contain the mandatory pattern when using
"string" or "rstring". If a large response is absolutely required, it is
possible to change the default max size by setting the global variable.
However, it is worth keeping in mind that parsing very large responses can
waste some CPU cycles, especially when regular expressions are used, and that
it is always better to focus the checks on smaller resources.

In an http-check ruleset, the last expect rule may be implicit. If no expect
rule is specified after the last "http-check send", an implicit expect rule
is defined to match on 2xx or 3xx status codes. It means this rule is also
defined if there is no "http-check" rule at all, when only "option httpchk"
is set.

Last, if "http-check expect" is combined with "http-check disable-on-404",
then this last one has precedence when the server responds with 404.
Examples :
# only accept status 200 as valid
http-check expect status 200,201,300-310

# be sure a sessid coookie is set
http-check expect header name "set-cookie" value -m beg "sessid="

# consider SQL errors as errors
http-check expect ! string SQL\ Error

# consider status 5xx only as errors
http-check expect ! rstatus ^5

# check that we have a correct hexadecimal tag before /html
http-check expect rstring <!--tag:[0-9a-f]*--></html>
http-check send [meth <method>] [{ uri <uri> | uri-lf <fmt> }>] [ver <version>] [hdr <name> <fmt>]* [{ body <string> | body-lf <fmt> }] [comment <msg>]
Add a possible list of headers and/or a body to the request sent during HTTP
health checks.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
comment <msg>  defines a message to report if the rule evaluation fails.

meth <method>  is the optional HTTP method used with the requests. When not
               set, the "OPTIONS" method is used, as it generally requires
               low server processing and is easy to filter out from the
               logs. Any method may be used, though it is not recommended
               to invent non-standard ones.

uri <uri>      is optional and set the URI referenced in the HTTP requests
               to the string <uri>. It defaults to "/" which is accessible
               by default on almost any server, but may be changed to any
               other URI. Query strings are permitted.

uri-lf <fmt>   is optional and set the URI referenced in the HTTP requests
               using the log-format string <fmt>. It defaults to "/" which
               is accessible by default on almost any server, but may be
               changed to any other URI. Query strings are permitted.

ver <version>  is the optional HTTP version string. It defaults to
               "HTTP/1.0" but some servers might behave incorrectly in HTTP
               1.0, so turning it to HTTP/1.1 may sometimes help. Note that
               the Host field is mandatory in HTTP/1.1, use "hdr" argument
               to add it.

hdr <name> <fmt>  adds the HTTP header field whose name is specified in
                  <name> and whose value is defined by <fmt>, which follows
                  to the log-format rules.

body <string>  add the body defined by <string> to the request sent during
               HTTP health checks. If defined, the "Content-Length" header
               is thus automatically added to the request.

body-lf <fmt>  add the body defined by the log-format string <fmt> to the
               request sent during HTTP health checks. If defined, the
               "Content-Length" header is thus automatically added to the
               request.
In addition to the request line defined by the "option httpchk" directive,
this one is the valid way to add some headers and optionally a body to the
request sent during HTTP health checks. If a body is defined, the associate
"Content-Length" header is automatically added. Thus, this header or
"Transfer-encoding" header should not be present in the request provided by
"http-check send". If so, it will be ignored. The old trick consisting to add
headers after the version string on the "option httpchk" line is now
deprecated.

Also "http-check send" doesn't support HTTP keep-alive. Keep in mind that it
will automatically append a "Connection: close" header, unless a Connection
header has already already been configured via a hdr entry.

Note that the Host header and the request authority, when both defined, are
automatically synchronized. It means when the HTTP request is sent, when a
Host is inserted in the request, the request authority is accordingly
updated. Thus, don't be surprised if the Host header value overwrites the
configured request authority.

Note also for now, no Host header is automatically added in HTTP/1.1 or above
requests. You should add it explicitly.
Enable emission of a state header with HTTP health checks

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
When this option is set, HAProxy will systematically send a special header
"X-Haproxy-Server-State" with a list of parameters indicating to each server
how they are seen by HAProxy. This can be used for instance when a server is
manipulated without access to HAProxy and the operator needs to know whether
HAProxy still sees it up or not, or if the server is the last one in a farm.

The header is composed of fields delimited by semi-colons, the first of which
is a word ("UP", "DOWN", "NOLB"), possibly followed by a number of valid
checks on the total number before transition, just as appears in the stats
interface. Next headers are in the form "<variable>=<value>", indicating in
no specific order some values available in the stats interface :
  - a variable "address", containing the address of the backend server.
    This corresponds to the <address> field in the server declaration. For
    unix domain sockets, it will read "unix".

  - a variable "port", containing the port of the backend server. This
    corresponds to the <port> field in the server declaration. For unix
    domain sockets, it will read "unix".

  - a variable "name", containing the name of the backend followed by a slash
    ("/") then the name of the server. This can be used when a server is
    checked in multiple backends.

  - a variable "node" containing the name of the HAProxy node, as set in the
    global "node" variable, otherwise the system's hostname if unspecified.

  - a variable "weight" indicating the weight of the server, a slash ("/")
    and the total weight of the farm (just counting usable servers). This
    helps to know if other servers are available to handle the load when this
    one fails.

  - a variable "scur" indicating the current number of concurrent connections
    on the server, followed by a slash ("/") then the total number of
    connections on all servers of the same backend.

  - a variable "qcur" indicating the current number of requests in the
    server's queue.

Example of a header received by the application server :
  >>>  X-Haproxy-Server-State: UP 2/3; name=bck/srv2; node=lb1; weight=1/2; \
         scur=13/22; qcur=0
http-check set-var(<var-name>[,<cond>...]) <expr>
http-check set-var-fmt(<var-name>[,<cond>...]) <fmt>
This operation sets the content of a variable. The variable is declared inline.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed for http-check are:
              "proc" : the variable is shared with the whole process.
              "sess" : the variable is shared with the tcp-check session.
              "check": the variable is declared for the lifetime of the tcp-check.
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9', '.',
            and '-'.

<cond>      A set of conditions that must all be true for the variable to
            actually be set (such as "ifnotempty", "ifgt" ...). See the
            set-var converter's description for a full list of possible
            conditions.

<expr>      Is a sample-fetch expression potentially followed by converters.

<fmt>       This is the value expressed using log-format rules (see Custom
            Log Format in section 8.2.4).
Examples :
http-check set-var(check.port) int(1234)
http-check set-var-fmt(check.port) "name=%H"
Free a reference to a variable within its scope.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed for http-check are:
              "proc" : the variable is shared with the whole process.
              "sess" : the variable is shared with the tcp-check session.
              "check": the variable is declared for the lifetime of the tcp-check.
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9', '.',
            and '-'.
Examples :
http-check unset-var(check.port)
http-error status <code> [content-type <type>] [ { default-errorfiles | errorfile <file> | errorfiles <name> | file <file> | lf-file <file> | string <str> | lf-string <fmt> } ] [ hdr <name> <fmt> ]*
Defines a custom error message to use instead of errors generated by HAProxy.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
status <code>        is the HTTP status code. It must be specified.
                     Currently, HAProxy is capable of generating codes
                     200, 400, 401, 403, 404, 405, 407, 408, 410, 413, 425,
                     429, 500, 501, 502, 503, and 504.

content-type <type>  is the response content type, for instance
                     "text/plain". This parameter is ignored and should be
                     omitted when an errorfile is configured or when the
                     payload is empty. Otherwise, it must be defined.

default-errorfiles   Reset the previously defined error message for current
                     proxy for the status <code>. If used on a backend, the
                     frontend error message is used, if defined. If used on
                     a frontend, the default error message is used.

errorfile <file>     designates a file containing the full HTTP response.
                     It is recommended to follow the common practice of
                     appending ".http" to the filename so that people do
                     not confuse the response with HTML error pages, and to
                     use absolute paths, since files are read before any
                     chroot is performed.

errorfiles <name>    designates the http-errors section to use to import
                     the error message with the status code <code>. If no
                     such message is found, the proxy's error messages are
                     considered.

file <file>          specifies the file to use as response payload. If the
                     file is not empty, its content-type must be set as
                     argument to "content-type", otherwise, any
                     "content-type" argument is ignored. <file> is
                     considered as a raw string.

string <str>         specifies the raw string to use as response payload.
                     The content-type must always be set as argument to
                     "content-type".

lf-file <file>       specifies the file to use as response payload. If the
                     file is not empty, its content-type must be set as
                     argument to "content-type", otherwise, any
                     "content-type" argument is ignored. <file> is
                     evaluated as a log-format string.

lf-string <str>      specifies the log-format string to use as response
                     payload. The content-type must always be set as
                     argument to "content-type".

hdr <name> <fmt>     adds to the response the HTTP header field whose name
                     is specified in <name> and whose value is defined by
                     <fmt>, which follows to the log-format rules.
                     This parameter is ignored if an errorfile is used.
This directive may be used instead of "errorfile", to define a custom error
message. As "errorfile" directive, it is used for errors detected and
returned by HAProxy. If an errorfile is defined, it is parsed when HAProxy
starts and must be valid according to the HTTP standards. The generated
response must not exceed the configured buffer size (BUFFSIZE), otherwise an
internal error will be returned.  Finally, if you consider to use some
http-after-response rules to rewrite these errors, the reserved buffer space
should be available (see "tune.maxrewrite").

The files are read at the same time as the configuration and kept in memory.
For this reason, the errors continue to be returned even when the process is
chrooted, and no file change is considered while the process is running.

Note: 400/408/500 errors emitted in early stage of the request parsing are
      handled by the multiplexer at a lower level. No custom formatting is
      supported at this level. Thus only static error messages, defined with
      "errorfile" directive, are supported. However, this limitation only
      exists during the request headers parsing or between two transactions.
http-request <action> [options...] [ { if | unless } <condition> ]
Access control for Layer 7 requests

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes(!)
yes(!)
yes
yes
yes
yes
yes
yes
The http-request statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Any rule may optionally be
followed by an ACL-based condition, in which case it will only be evaluated
if the condition evaluates to true.

The condition is evaluated just before the action is executed, and the action
is performed exactly once. As such, there is no problem if an action changes
an element which is checked as part of the condition. This also means that
multiple actions may rely on the same condition so that the first action that
changes the condition's evaluation is sufficient to implicitly disable the
remaining actions. This is used for example when trying to assign a value to
a variable from various sources when it's empty. There is no limit to the
number of "http-request" statements per instance.

The first keyword after "http-request" in the syntax is the rule's action,
optionally followed by a varying number of arguments for the action. The
supported actions and their respective syntaxes are enumerated in section 4.3
"Actions" (look for actions which tick "HTTP Req").

This directive is only available from named defaults sections, not anonymous
ones. Rules defined in the defaults section are evaluated before ones in the
associated proxy section. To avoid ambiguities, in this case the same
defaults section cannot be used by proxies with the frontend capability and
by proxies with the backend capability. It means a listen section cannot use
a defaults section defining such rules.
Example:
acl nagios src 192.168.129.3
acl local_net src 192.168.0.0/16
acl auth_ok http_auth(L1)

http-request allow if nagios
http-request allow if local_net auth_ok
http-request auth realm Gimme if local_net auth_ok
http-request deny
Example:
acl key req.hdr(X-Add-Acl-Key) -m found
acl add path /addacl
acl del path /delacl

acl myhost hdr(Host) -f myhost.lst

http-request add-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key add
http-request del-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key del
Example:
acl value  req.hdr(X-Value) -m found
acl setmap path /setmap
acl delmap path /delmap

use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }

http-request set-map(map.lst) %[src] %[req.hdr(X-Value)] if setmap value
http-request del-map(map.lst) %[src]                     if delmap
http-response <action> <options...> [ { if | unless } <condition> ]
Access control for Layer 7 responses

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes(!)
yes(!)
yes
yes
yes
yes
yes
yes
The http-response statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Since these rules apply on
responses, the backend rules are applied first, followed by the frontend's
rules. Any rule may optionally be followed by an ACL-based condition, in
which case it will only be evaluated if the condition evaluates to true.

The condition is evaluated just before the action is executed, and the action
is performed exactly once. As such, there is no problem if an action changes
an element which is checked as part of the condition. This also means that
multiple actions may rely on the same condition so that the first action that
changes the condition's evaluation is sufficient to implicitly disable the
remaining actions. This is used for example when trying to assign a value to
a variable from various sources when it's empty. There is no limit to the
number of "http-response" statements per instance.

The first keyword after "http-response" in the syntax is the rule's action,
optionally followed by a varying number of arguments for the action. The
supported actions and their respective syntaxes are enumerated in section 4.3
"Actions" (look for actions which tick "HTTP Res").

This directive is only available from named defaults sections, not anonymous
ones. Rules defined in the defaults section are evaluated before ones in the
associated proxy section. To avoid ambiguities, in this case the same
defaults section cannot be used by proxies with the frontend capability and
by proxies with the backend capability. It means a listen section cannot use
a defaults section defining such rules.
Example:
acl key_acl res.hdr(X-Acl-Key) -m found

acl myhost hdr(Host) -f myhost.lst

http-response add-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl
http-response del-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl
Example:
acl value  res.hdr(X-Value) -m found

use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }

http-response set-map(map.lst) %[src] %[res.hdr(X-Value)] if value
http-response del-map(map.lst) %[src]                     if ! value
http-reuse { never | safe | aggressive | always }
Declare how idle HTTP connections may be shared between requests

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
By default, a connection established between HAProxy and the backend server
which is considered safe for reuse is moved back to the server's idle
connections pool so that any other request can make use of it. This is the
"safe" strategy below.

The argument indicates the desired connection reuse strategy :

  - "never"  : idle connections are never shared between sessions. This mode
               may be enforced to cancel a different strategy inherited from
               a defaults section or for troubleshooting. For example, if an
               old bogus application considers that multiple requests over
               the same connection come from the same client and it is not
               possible to fix the application, it may be desirable to
               disable connection sharing in a single backend. An example of
               such an application could be an old HAProxy using cookie
               insertion in tunnel mode and not checking any request past the
               first one.

  - "safe"   : this is the default and the recommended strategy. The first
               request of a session is always sent over its own connection,
               and only subsequent requests may be dispatched over other
               existing connections. This ensures that in case the server
               closes the connection when the request is being sent, the
               browser can decide to silently retry it. Since it is exactly
               equivalent to regular keep-alive, there should be no side
               effects. There is also a special handling for the connections
               using protocols subject to Head-of-line blocking (backend with
               h2 or fcgi). In this case, when at least one stream is
               processed, the used connection is reserved to handle streams
               of the same session. When no more streams are processed, the
               connection is released and can be reused.

  - "aggressive" : this mode may be useful in webservices environments where
               all servers are not necessarily known and where it would be
               appreciable to deliver most first requests over existing
               connections. In this case, first requests are only delivered
               over existing connections that have been reused at least once,
               proving that the server correctly supports connection reuse.
               It should only be used when it's sure that the client can
               retry a failed request once in a while and where the benefit
               of aggressive connection reuse significantly outweighs the
               downsides of rare connection failures.

  - "always" : this mode is only recommended when the path to the server is
               known for never breaking existing connections quickly after
               releasing them. It allows the first request of a session to be
               sent to an existing connection. This can provide a significant
               performance increase over the "safe" strategy when the backend
               is a cache farm, since such components tend to show a
               consistent behavior and will benefit from the connection
               sharing. It is recommended that the "http-keep-alive" timeout
               remains low in this mode so that no dead connections remain
               usable. In most cases, this will lead to the same performance
               gains as "aggressive" but with more risks. It should only be
               used when it improves the situation over "aggressive".

When http connection sharing is enabled, a great care is taken to respect the
connection properties and compatibility. Indeed, some properties are specific
and it is not possible to reuse it blindly. Those are the SSL SNI, source
and destination address, proxy protocol block as well as tos and mark
sockopts. A connection is reused only if it shares the same set of properties
with the request.

Also note that connections with certain bogus authentication schemes (relying
on the connection) like NTLM are marked private and never shared.

A connection pool is involved and configurable with "pool-max-conn".

Note: connection reuse improves the accuracy of the "server maxconn" setting,
because almost no new connection will be established while idle connections
remain available. This is particularly true with the "always" strategy.

The rules to decide to keep an idle connection opened or to close it after
processing are also governed by the "tune.pool-low-fd-ratio" (default: 20%)
and "tune.pool-high-fd-ratio" (default: 25%). These correspond to the
percentage of total file descriptors spent in idle connections above which
haproxy will respectively refrain from keeping a connection opened after a
response, and actively kill idle connections. Some setups using a very high
ratio of idle connections, either because of too low a global "maxconn", or
due to a lot of HTTP/2 or HTTP/3 traffic on the frontend (few connections)
but HTTP/1 connections on the backend, may observe a lower reuse rate because
too few connections are kept open. It may be desirable in this case to adjust
such thresholds or simply to increase the global "maxconn" value.

Similarly, when thread groups are explicitly enabled, it is important to
understand that idle connections are only usable between threads from a same
group. As such it may happen that unfair load between groups leads to more
idle connections being needed, causing a lower reuse rate. The same solution
may then be applied (increase global "maxconn" or increase pool ratios).
Add the server name to a request. Use the header string given by <header>

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<header>  The header string to use to send the server name
The "http-send-name-header" statement causes the header field named <header>
to be set to the name of the target server at the moment the request is about
to be sent on the wire. Any existing occurrences of this header are removed.
Upon retries and redispatches, the header field is updated to always reflect
the server being attempted to connect to. Given that this header is modified
very late in the connection setup, it may have unexpected effects on already
modified headers. For example using it with transport-level header such as
connection, content-length, transfer-encoding and so on will likely result in
invalid requests being sent to the server. Additionally it has been reported
that this directive is currently being used as a way to overwrite the Host
header field in outgoing requests; while this trick has been known to work
as a side effect of the feature for some time, it is not officially supported
and might possibly not work anymore in a future version depending on the
technical difficulties this feature induces. A long-term solution instead
consists in fixing the application which required this trick so that it binds
to the correct host name.
id <value>
Set a persistent ID to a proxy.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
yes
yes
Arguments : none
Set a persistent ID for the proxy. This ID must be unique and positive.
An unused ID will automatically be assigned if unset. The first assigned
value will be 1. This ID is currently only returned in statistics.
ignore-persist { if | unless } <condition>
Declare a condition to ignore persistence

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
no
no
no
no
yes
yes
yes
yes
By default, when cookie persistence is enabled, every requests containing
the cookie are unconditionally persistent (assuming the target server is up
and running).

The "ignore-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore persistence.
This is sometimes useful to load balance requests for static files, which
often don't require persistence. This can also be used to fully disable
persistence for a specific User-Agent (for example, some web crawler bots).

The persistence is ignored when an "if" condition is met, or unless an
"unless" condition is met.
Example:
acl url_static  path_beg         /static /images /img /css
acl url_static  path_end         .gif .png .jpg .css .js
ignore-persist  if url_static
load-server-state-from-file { global | local | none }
Allow seamless reload of HAProxy

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
This directive points HAProxy to a file where server state from previous
running process has been saved. That way, when starting up, before handling
traffic, the new process can apply old states to servers exactly has if no
reload occurred. The purpose of the "load-server-state-from-file" directive is
to tell HAProxy which file to use. For now, only 2 arguments to either prevent
loading state or load states from a file containing all backends and servers.
The state file can be generated by running the command "show servers state"
over the stats socket and redirect output.

The format of the file is versioned and is very specific. To understand it,
please read the documentation of the "show servers state" command (chapter
9.3 of Management Guide).
Arguments:
global     load the content of the file pointed by the global directive
           named "server-state-file".

local      load the content of the file pointed by the directive
           "server-state-file-name" if set. If not set, then the backend
           name is used as a file name.

none       don't load any stat for this backend
Notes:
  - server's IP address is preserved across reloads by default, but the
    order can be changed thanks to the server's "init-addr" setting. This
    means that an IP address change performed on the CLI at run time will
    be preserved, and that any change to the local resolver (e.g. /etc/hosts)
    will possibly not have any effect if the state file is in use.

  - server's weight is applied from previous running process unless it has
    has changed between previous and new configuration files.
Example:
Minimal configuration
global stats socket /tmp/socket server-state-file /tmp/server_state defaults load-server-state-from-file global backend bk server s1 127.0.0.1:22 check weight 11 server s2 127.0.0.1:22 check weight 12
Then one can run :

  socat /tmp/socket - <<< "show servers state" > /tmp/server_state

Content of the file /tmp/server_state would be like this:

  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0
Example:
Minimal configuration
global stats socket /tmp/socket server-state-base /etc/haproxy/states defaults load-server-state-from-file local backend bk server s1 127.0.0.1:22 check weight 11 server s2 127.0.0.1:22 check weight 12
Then one can run :

  socat /tmp/socket - <<< "show servers state bk" > /etc/haproxy/states/bk

Content of the file /etc/haproxy/states/bk would be like this:

  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0
log <target> [len <length>] [format <format>] [sample <ranges>:<sample_size>] <facility> [<level> [<minlevel>]]
Enable per-instance logging of events and traffic.

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Prefix :
  no         should be used when the logger list must be flushed. For example,
             if you don't want to inherit from the default logger list. This
             prefix does not allow arguments.
Arguments :
global     should be used when the instance's logging parameters are the
           same as the global ones. This is the most common usage. "global"
           replaces <target>, <facility> and <level> with those of the log
           entries found in the "global" section. Only one "log global"
           statement may be used per instance, and this form takes no other
           parameter.

<target>   indicates where to send the logs. It takes the same format as
           for the "global" section's logs, and can be one of :

           - An IPv4 address optionally followed by a colon (':') and a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).

           - An IPv6 address followed by a colon (':') and optionally a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).

           - A filesystem path to a UNIX domain socket, keeping in mind
             considerations for chroot (be sure the path is accessible
             inside the chroot) and uid/gid (be sure the path is
             appropriately writable).

           - A file descriptor number in the form "fd@<number>", which may
             point to a pipe, terminal, or socket. In this case unbuffered
             logs are used and one writev() call per log is performed. This
             is a bit expensive but acceptable for most workloads. Messages
             sent this way will not be truncated but may be dropped, in
             which case the DroppedLogs counter will be incremented. The
             writev() call is atomic even on pipes for messages up to
             PIPE_BUF size, which POSIX recommends to be at least 512 and
             which is 4096 bytes on most modern operating systems. Any
             larger message may be interleaved with messages from other
             processes.  Exceptionally for debugging purposes the file
             descriptor may also be directed to a file, but doing so will
             significantly slow HAProxy down as non-blocking calls will be
             ignored. Also there will be no way to purge nor rotate this
             file without restarting the process. Note that the configured
             syslog format is preserved, so the output is suitable for use
             with a TCP syslog server. See also the "short" and "raw"
             formats below.

           - "stdout" / "stderr", which are respectively aliases for "fd@1"
             and "fd@2", see above.

           - A ring buffer in the form "ring@<name>", which will correspond
             to an in-memory ring buffer accessible over the CLI using the
             "show events" command, which will also list existing rings and
             their sizes. Such buffers are lost on reload or restart but
             when used as a complement this can help troubleshooting by
             having the logs instantly available.

           - A log backend in the form "backend@<name>", which will send
             log messages to the corresponding log backend responsible for
             sending the message to the proper server according to the
             backend's lb settings. A log backend is a backend section with
             "mode log" set (see "mode" for more information).

           - An explicit stream address prefix such as "tcp@","tcp6@",
             "tcp4@" or "uxst@" will allocate an implicit ring buffer with
             a stream forward server targeting the given address.

           You may want to reference some environment variables in the
           address parameter, see section 2.3 about environment variables.

<length>   is an optional maximum line length. Log lines larger than this
           value will be truncated before being sent. The reason is that
           syslog servers act differently on log line length. All servers
           support the default value of 1024, but some servers simply drop
           larger lines while others do log them. If a server supports long
           lines, it may make sense to set this value here in order to avoid
           truncating long lines. Similarly, if a server drops long lines,
           it is preferable to truncate them before sending them. Accepted
           values are 80 to 65535 inclusive. The default value of 1024 is
           generally fine for all standard usages. Some specific cases of
           long captures or JSON-formatted logs may require larger values.
           You may also need to increase "tune.http.logurilen" if your
           request URIs are truncated.

<ranges>   A list of comma-separated ranges to identify the logs to sample.
           This is used to balance the load of the logs to send to the log
           server. The limits of the ranges cannot be null. They are numbered
           from 1. The size or period (in number of logs) of the sample must
           be set with <sample_size> parameter.

<sample_size>
           The size of the sample in number of logs to consider when balancing
           their logging loads. It is used to balance the load of the logs to
           send to the syslog server. This size must be greater or equal to the
           maximum of the high limits of the ranges.
           (see also <ranges> parameter).

<format> is the log format used when generating syslog messages. It may be
         one of the following :

  local     Analog to rfc3164 syslog message format except that hostname
            field is stripped. This is the default.
            Note: option "log-send-hostname" switches the default to
            rfc3164.

  rfc3164   The RFC3164 syslog message format.
            (https://tools.ietf.org/html/rfc3164)

  rfc5424   The RFC5424 syslog message format.
            (https://tools.ietf.org/html/rfc5424)

  priority  A message containing only a level plus syslog facility between
            angle brackets such as '<63>', followed by the text. The PID,
            date, time, process name and system name are omitted. This is
            designed to be used with a local log server.

  short     A message containing only a level between angle brackets such as
            '<3>', followed by the text. The PID, date, time, process name
            and system name are omitted. This is designed to be used with a
            local log server. This format is compatible with what the
            systemd logger consumes.

  timed     A message containing only a level between angle brackets such as
            '<3>', followed by ISO date and by the text. The PID, process
            name and system name are omitted. This is designed to be
            used with a local log server.

  iso       A message containing only the ISO date, followed by the text.
            The PID, process name and system name are omitted. This is
            designed to be used with a local log server.

  raw       A message containing only the text. The level, PID, date, time,
            process name and system name are omitted. This is designed to
            be used in containers or during development, where the severity
            only depends on the file descriptor used (stdout/stderr).

<facility> must be one of the 24 standard syslog facilities :

               kern   user   mail   daemon auth   syslog lpr    news
               uucp   cron   auth2  ftp    ntp    audit  alert  cron2
               local0 local1 local2 local3 local4 local5 local6 local7

           Note that the facility is ignored for the "short" and "raw"
           formats, but still required as a positional field. It is
           recommended to use "daemon" in this case to make it clear that
           it's only supposed to be used locally.

<level>    is optional and can be specified to filter outgoing messages. By
           default, all messages are sent. If a level is specified, only
           messages with a severity at least as important as this level
           will be sent. An optional minimum level can be specified. If it
           is set, logs emitted with a more severe level than this one will
           be capped to this level. This is used to avoid sending "emerg"
           messages on all terminals on some default syslog configurations.
           Eight levels are known :

             emerg  alert  crit   err    warning notice info  debug
It is important to keep in mind that it is the frontend which decides what to
log from a connection, and that in case of content switching, the log entries
from the backend will be ignored. Connections are logged at level "info".

However, backend log declaration define how and where servers status changes
will be logged. Level "notice" will be used to indicate a server going up,
"warning" will be used for termination signals and definitive service
termination, and "alert" will be used for when a server goes down.

Note : According to RFC3164, messages are truncated to 1024 bytes before
       being emitted.
Example :
log global
log stdout format short daemon          # send log to systemd
log stdout format raw daemon            # send everything to stdout
log stderr format raw daemon notice     # send important events to stderr
log 127.0.0.1:514 local0 notice         # only send important events
log tcp@127.0.0.1:514 local0 notice notice  # same but limit output
                                            # level and send in tcp
log "${LOCAL_SYSLOG}:514" local0 notice   # send to local server
log-format <string>
Specifies the log format string to use for traffic logs

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
This directive specifies the log format string that will be used for all logs
resulting from traffic passing through the frontend using this line. If the
directive is used in a defaults section, all subsequent frontends will use
the same log format. Please see section 8.2.4 which covers the log format
string in depth.
A specific log-format used only in case of connection error can also be
defined, see the "error-log-format" option.

"log-format" directive overrides previous "option tcplog", "log-format",
"option httplog" and "option httpslog" directives.
log-format-sd <string>
Specifies the RFC5424 structured-data log format string

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
This directive specifies the RFC5424 structured-data log format string that
will be used for all logs resulting from traffic passing through the frontend
using this line. If the directive is used in a defaults section, all
subsequent frontends will use the same log format. Please see section 8.2.4
which covers the log format string in depth.

See https://tools.ietf.org/html/rfc5424#section-6.3 for more information
about the RFC5424 structured-data part.

Note : This log format string will be used only for loggers that have set
       log format to "rfc5424".
Example :
log-format-sd [exampleSDID@1234\ bytes=\"%B\"\ status=\"%ST\"]
log-tag <string>
Specifies the log tag to use for all outgoing logs

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Sets the tag field in the syslog header to this string. It defaults to the
log-tag set in the global section, otherwise the program name as launched
from the command line, which usually is "HAProxy". Sometimes it can be useful
to differentiate between multiple processes running on the same host, or to
differentiate customer instances running in the same process. In the backend,
logs about servers up/down will use this tag. As a hint, it can be convenient
to set a log-tag related to a hosted customer in a defaults section then put
all the frontends and backends for that customer, then start another customer
in a new defaults section. See also the global "log-tag" directive.
Set the maximum server queue size for maintaining keep-alive connections

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
HTTP keep-alive tries to reuse the same server connection whenever possible,
but sometimes it can be counter-productive, for example if a server has a lot
of connections while other ones are idle. This is especially true for static
servers.

The purpose of this setting is to set a threshold on the number of queued
connections at which HAProxy stops trying to reuse the same server and prefers
to find another one. The default value, -1, means there is no limit. A value
of zero means that keep-alive requests will never be queued. For very close
servers which can be reached with a low latency and which are not sensible to
breaking keep-alive, a low value is recommended (e.g. local static server can
use a value of 10 or less). For remote servers suffering from a high latency,
higher values might be needed to cover for the latency and/or the cost of
picking a different server.

Note that this has no impact on responses which are maintained to the same
server consecutively to a 401 response. They will still go to the same server
even if they have to be queued.
Set the maximum number of outgoing connections we can keep idling for a given
client session. The default is 5 (it precisely equals MAX_SRV_LIST which is
defined at build time).

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
maxconn <conns>
Fix the maximum number of concurrent connections on a frontend

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<conns>   is the maximum number of concurrent connections the frontend will
          accept to serve. Excess connections will be queued by the system
          in the socket's listen queue and will be served once a connection
          closes.
If the system supports it, it can be useful on big sites to raise this limit
very high so that HAProxy manages connection queues, instead of leaving the
clients with unanswered connection attempts. This value should not exceed the
global maxconn. Also, keep in mind that a connection contains two buffers
of tune.bufsize (16kB by default) each, as well as some other data resulting
in about 33 kB of RAM being consumed per established connection. That means
that a medium system equipped with 1GB of RAM can withstand around
20000-25000 concurrent connections if properly tuned.

Also, when <conns> is set to large values, it is possible that the servers
are not sized to accept such loads, and for this reason it is generally wise
to assign them some reasonable connection limits.

When this value is set to zero, which is the default, the global "maxconn"
value is used.
mode { tcp|http|log }
Set the running mode or protocol of the instance

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
tcp       The instance will work in pure TCP mode. A full-duplex connection
          will be established between clients and servers, and no layer 7
          examination will be performed. This is the default mode. It
          should be used for SSL, SSH, SMTP, ...

http      The instance will work in HTTP mode. The client request will be
          analyzed in depth before connecting to any server. Any request
          which is not RFC-compliant will be rejected. Layer 7 filtering,
          processing and switching will be possible. This is the mode which
          brings HAProxy most of its value.

log       When used in a backend section, it will turn the backend into a
          log backend. Such backend can be used as a log destination for
          any "log" directive by using the "backend@<name>" syntax. Log
          messages will be distributed to the servers from the backend
          according to the lb settings which can be configured using the
          "balance" keyword. Log backends support UDP servers by prefixing
          the server's address with the "udp@" prefix. Common backend and
          server features are supported, but not TCP or HTTP specific ones.
When doing content switching, it is mandatory that the frontend and the
backend are in the same mode (generally HTTP), otherwise the configuration
will be refused.
Example :
defaults http_instances
    mode http
monitor fail { if | unless } <condition>
Add a condition to report a failure to a monitor HTTP request.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
no
no
yes
yes
yes
yes
no
no
Arguments :
if <cond>     the monitor request will fail if the condition is satisfied,
              and will succeed otherwise. The condition should describe a
              combined test which must induce a failure if all conditions
              are met, for instance a low number of servers both in a
              backend and its backup.

unless <cond> the monitor request will succeed only if the condition is
              satisfied, and will fail otherwise. Such a condition may be
              based on a test on the presence of a minimum number of active
              servers in a list of backends.
This statement adds a condition which can force the response to a monitor
request to report a failure. By default, when an external component queries
the URI dedicated to monitoring, a 200 response is returned. When one of the
conditions above is met, HAProxy will return 503 instead of 200. This is
very useful to report a site failure to an external component which may base
routing advertisements between multiple sites on the availability reported by
HAProxy. In this case, one would rely on an ACL involving the "nbsrv"
criterion. Note that "monitor fail" only works in HTTP mode. Both status
messages may be tweaked using "errorfile" or "errorloc" if needed.
Example:
frontend www
   mode http
   acl site_dead nbsrv(dynamic) lt 2
   acl site_dead nbsrv(static)  lt 2
   monitor-uri   /site_alive
   monitor fail  if site_dead
Intercept a URI used by external components' monitor requests

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments :
<uri>     is the exact URI which we want to intercept to return HAProxy's
          health status instead of forwarding the request.
When an HTTP request referencing <uri> will be received on a frontend,
HAProxy will not forward it nor log it, but instead will return either
"HTTP/1.0 200 OK" or "HTTP/1.0 503 Service unavailable", depending on failure
conditions defined with "monitor fail". This is normally enough for any
front-end HTTP probe to detect that the service is UP and running without
forwarding the request to a backend server. Note that the HTTP method, the
version and all headers are ignored, but the request must at least be valid
at the HTTP level. This keyword may only be used with an HTTP-mode frontend.

Monitor requests are processed very early, just after the request is parsed
and even before any "http-request". The only rulesets applied before are the
tcp-request ones. They cannot be logged either, and it is the intended
purpose. Only one URI may be configured for monitoring; when multiple
"monitor-uri" statements are present, the last one will define the URI to
be used. They are only used to report HAProxy's health to an upper component,
nothing more. However, it is possible to add any number of conditions using
"monitor fail" and ACLs so that the result can be adjusted to whatever check
can be imagined (most often the number of available servers in a backend).

Note: if <uri> starts by a slash ('/'), the matching is performed against the
      request's path instead of the request's uri. It is a workaround to let
      the HTTP/2 requests match the monitor-uri. Indeed, in HTTP/2, clients
      are encouraged to send absolute URIs only.
Example :
# Use /haproxy_test to report HAProxy's status
frontend www
    mode http
    monitor-uri /haproxy_test
Enable or disable early dropping of aborted requests pending in queues.

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
In presence of very high loads, the servers will take some time to respond.
The per-instance connection queue will inflate, and the response time will
increase respective to the size of the queue times the average per-stream
response time. When clients will wait for more than a few seconds, they will
often hit the "STOP" button on their browser, leaving a useless request in
the queue, and slowing down other users, and the servers as well, because the
request will eventually be served, then aborted at the first error
encountered while delivering the response.

As there is no way to distinguish between a full STOP and a simple output
close on the client side, HTTP agents should be conservative and consider
that the client might only have closed its output channel while waiting for
the response. However, this introduces risks of congestion when lots of users
do the same, and is completely useless nowadays because probably no client at
all will close the stream while waiting for the response. Some HTTP agents
support this behavior (Squid, Apache, HAProxy), and others do not (TUX, most
hardware-based load balancers). So the probability for a closed input channel
to represent a user hitting the "STOP" button is close to 100%, and the risk
of being the single component to break rare but valid traffic is extremely
low, which adds to the temptation to be able to abort a stream early while
still not served and not pollute the servers.

In HAProxy, the user can choose the desired behavior using the option
"abortonclose". By default (without the option) the behavior is HTTP
compliant and aborted requests will be served. But when the option is
specified, a stream with an incoming channel closed will be aborted while
it is still possible, either pending in the queue for a connection slot, or
during the connection establishment if the server has not yet acknowledged
the connection request. This considerably reduces the queue size and the load
on saturated servers when users are tempted to click on STOP, which in turn
reduces the response time for other users.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable relaxing of HTTP request parsing

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. Similarly, the
list of characters allowed to appear in a URI is well defined by RFC3986, and
chars 0-31, 32 (space), 34 ('"'), 60 ('<'), 62 ('>'), 92 ('\'), 94 ('^'), 96
('`'), 123 ('{'), 124 ('|'), 125 ('}'), 127 (delete) and anything above are
not allowed at all. HAProxy always blocks a number of them (0..32, 127). The
remaining ones are blocked by default unless this option is enabled. This
option also relaxes the test on the HTTP version, it allows HTTP/0.9 requests
to pass through (no version specified), as well as different protocol names
(e.g. RTSP), and multiple digits for both the major and the minor version.
Finally, this option also allows incoming URLs to contain fragment references
('#' after the path).

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
requests, but the complete request will be captured in order to permit later
analysis using the "show errors" request on the UNIX stats socket. Similarly,
requests containing invalid chars in the URI part will be logged. Doing this
also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable relaxing of HTTP response parsing

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. This option also
relaxes the test on the HTTP version format, it allows multiple digits for
both the major and the minor version.

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
responses, but the complete response will be captured in order to permit
later analysis using the "show errors" request on the UNIX stats socket.
Doing this also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Use either all backup servers at a time or only the first one

May be used in the following contexts: tcp, http, log

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
By default, the first operational backup server gets all traffic when normal
servers are all down. Sometimes, it may be preferred to use multiple backups
at once, because one will not be enough. When "option allbackups" is enabled,
the load balancing will be performed among all backup servers when all normal
ones are unavailable. The same load balancing algorithm will be used and the
servers' weights will be respected. Thus, there will not be any priority
order between the backup servers anymore.

This option is mostly used with static server farms dedicated to return a
"sorry" page when an application is completely offline.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Analyze all server responses and block responses with cacheable cookies

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
Some high-level frameworks set application cookies everywhere and do not
always let enough control to the developer to manage how the responses should
be cached. When a session cookie is returned on a cacheable object, there is a
high risk of session crossing or stealing between users traversing the same
caches. In some situations, it is better to block the response than to let
some sensitive session information go in the wild.

The option "checkcache" enables deep inspection of all server responses for
strict compliance with HTTP specification in terms of cacheability. It
carefully checks "Cache-control", "Pragma" and "Set-cookie" headers in server
response to check if there's a risk of caching a cookie on a client-side
proxy. When this option is enabled, the only responses which can be delivered
to the client are :
  - all those without "Set-Cookie" header;
  - all those with a return code other than 200, 203, 204, 206, 300, 301,
    404, 405, 410, 414, 501, provided that the server has not set a
    "Cache-control: public" header field;
  - all those that result from a request using a method other than GET, HEAD,
    OPTIONS, TRACE, provided that the server has not set a 'Cache-Control:
    public' header field;
  - those with a 'Pragma: no-cache' header
  - those with a 'Cache-control: private' header
  - those with a 'Cache-control: no-store' header
  - those with a 'Cache-control: max-age=0' header
  - those with a 'Cache-control: s-maxage=0' header
  - those with a 'Cache-control: no-cache' header
  - those with a 'Cache-control: no-cache="set-cookie"' header
  - those with a 'Cache-control: no-cache="set-cookie,' header
    (allowing other fields after set-cookie)

If a response doesn't respect these requirements, then it will be blocked
just as if it was from an "http-response deny" rule, with an "HTTP 502 bad
gateway". The session state shows "PH--" meaning that the proxy blocked the
response during headers processing. Additionally, an alert will be sent in
the logs so that admins are informed that there's something to be fixed.

Due to the high impact on the application, the application should be tested
in depth with the option enabled before going to production. It is also a
good practice to always activate it during tests, even if it is not used in
production, as it will report potentially dangerous application behaviors.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable the sending of TCP keepalive packets on the client side

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "clitcpka" enables the emission of TCP keep-alive probes on the
client side of a connection, which should help when session expirations are
noticed between HAProxy and a client.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable continuous traffic statistics updates

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
By default, counters used for statistics calculation are incremented
only when a stream finishes. It works quite well when serving small
objects, but with big ones (for example large images or archives) or
with A/V streaming, a graph generated from HAProxy counters looks like
a hedgehog. With this option enabled counters get incremented frequently
along the stream, typically every 5 seconds, which is often enough to
produce clean graphs. Recounting touches a hotpath directly so it is not
not enabled by default, as it can cause a lot of wakeups for very large
session counts and cause a small performance drop.
Enable or disable the implicit HTTP/2 upgrade from an HTTP/1.x client
connection.

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
By default, HAProxy is able to implicitly upgrade an HTTP/1.x client
connection to an HTTP/2 connection if the first request it receives from a
given HTTP connection matches the HTTP/2 connection preface (i.e. the string
"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"). This way, it is possible to support
HTTP/1.x and HTTP/2 clients on a non-SSL connections. This option must be
used to disable the implicit upgrade. Note this implicit upgrade is only
supported for HTTP proxies, thus this option too. Note also it is possible to
force the HTTP/2 on clear connections by specifying "proto h2" on the bind
line. Finally, this option is applied on all bind lines. To disable implicit
HTTP/2 upgrades for a specific bind line, it is possible to use "proto h1".

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable logging of normal, successful connections

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
There are large sites dealing with several thousand connections per second
and for which logging is a major pain. Some of them are even forced to turn
logs off and cannot debug production issues. Setting this option ensures that
normal connections, those which experience no error, no timeout, no retry nor
redispatch, will not be logged. This leaves disk space for anomalies. In HTTP
mode, the response status code is checked and return codes 5xx will still be
logged.

It is strongly discouraged to use this option as most of the time, the key to
complex issues is in the normal logs which will not be logged here. If you
need to separate logs, see the "log-separate-errors" option instead.
Enable or disable logging of null connections

May be used in the following contexts: tcp, http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
In certain environments, there are components which will regularly connect to
various systems to ensure that they are still alive. It can be the case from
another load balancer as well as from monitoring systems. By default, even a
simple port probe or scan will produce a log. If those connections pollute
the logs too much, it is possible to enable option "dontlognull" to indicate
that a connection on which no data has been transferred will not be logged,
which typically corresponds to those probes. Note that errors will still be
returned to the client and accounted for in the stats. If this is not what is
desired, option http-ignore-probes can be used instead.

It is generally recommended not to use this option in uncontrolled
environments (e.g. internet), otherwise scans and other malicious activities
would not be logged.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
option forwarded [ proto ] [ host | host-expr <host_expr> ] [ by | by-expr <by_expr> ] [ by_port | by_port-expr <by_port_expr>] [ for | for-expr <for_expr> ] [ for_port | for_port-expr <for_port_expr>]
Enable insertion of the rfc 7239 forwarded header in requests sent to servers

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments :
<host_expr>     optional argument to specify a custom sample expression
                those result will be used as 'host' parameter value

<by_expr>       optional argument to specicy a custom sample expression
                those result will be used as 'by' parameter nodename value

<for_expr>      optional argument to specicy a custom sample expression
                those result will be used as 'for' parameter nodename value

<by_port_expr>  optional argument to specicy a custom sample expression
                those result will be used as 'by' parameter nodeport value

<for_port_expr> optional argument to specicy a custom sample expression
                those result will be used as 'for' parameter nodeport value
Since HAProxy works in reverse-proxy mode, servers are losing some request
context (request origin: client ip address, protocol used...)

A common way to address this limitation is to use the well known
x-forward-for and x-forward-* friends to expose some of this context to the
underlying servers/applications.
While this use to work and is widely deployed, it is not officially supported
by the IETF and can be the root of some interoperability as well as security
issues.

To solve this, a new HTTP extension has been described by the IETF:
forwarded header (RFC7239).
More information here: https://www.rfc-editor.org/rfc/rfc7239.html

The use of this single header allow to convey numerous details
within the same header, and most importantly, fixes the proxy chaining
issue. (the rfc allows for multiple chained proxies to append their own
values to an already existing header).

This option may be specified in defaults, listen or backend section, but it
will be ignored for frontend sections.

Setting option forwarded without arguments results in using default implicit
behavior.
Default behavior enables proto parameter and injects original client ip.

The equivalent explicit/manual configuration would be:
      option forwarded proto for

The keyword 'by' is used to enable 'by' parameter ("nodename") in
forwarded header. It allows to embed request proxy information.
'by' value will be set to proxy ip (destination address)
If not available (ie: UNIX listener), 'by' will be set to
"unknown".

The keyword 'by-expr' is used to enable 'by' parameter ("nodename") in
forwarded header. It allows to embed request proxy information.
'by' value will be set to the result of the sample expression
<by_expr>, if valid, otherwise it will be set to "unknown".

The keyword 'for' is used to enable 'for' parameter ("nodename") in
forwarded header. It allows to embed request client information.
'for' value will be set to client ip (source address)
If not available (ie: UNIX listener), 'for' will be set to
"unknown".

The keyword 'for-expr' is used to enable 'for' parameter ("nodename") in
forwarded header. It allows to embed request client information.
'for' value will be set to the result of the sample expression
<for_expr>, if valid, otherwise it will be set to "unknown".

The keyword 'by_port' is used to provide "nodeport" info to
'by' parameter. 'by_port' requires 'by' or 'by-expr' to be set or
it will be ignored.
"nodeport" will be set to proxy (destination) port if available,
otherwise it will be ignored.

The keyword 'by_port-expr' is used to provide "nodeport" info to
'by' parameter. 'by_port-expr' requires 'by' or 'by-expr' to be set or
it will be ignored.
"nodeport" will be set to the result of the sample expression
<by_port_expr>, if valid, otherwise it will be ignored.

The keyword 'for_port' is used to provide "nodeport" info to
'for' parameter. 'for_port' requires 'for' or 'for-expr' to be set or
it will be ignored.
"nodeport" will be set to client (source) port if available,
otherwise it will be ignored.

The keyword 'for_port-expr' is used to provide "nodeport" info to
'for' parameter. 'for_port-expr' requires 'for' or 'for-expr' to be set or
it will be ignored.
"nodeport" will be set to the result of the sample expression
<for_port_expr>, if valid, otherwise it will be ignored.
Examples :
# Those servers want the ip address and protocol of the client request
# Resulting header would look like this:
#   forwarded: proto=http;for=127.0.0.1
backend www_default
    mode http
    option forwarded
    #equivalent to: option forwarded proto for

# Those servers want the requested host and hashed client ip address
# as well as client source port (you should use seed for xxh32 if ensuring
# ip privacy is a concern)
# Resulting header would look like this:
#   forwarded: host="haproxy.org";for="_000000007F2F367E:60138"
backend www_host
    mode http
    option forwarded host for-expr src,xxh32,hex for_port

# Those servers want custom data in host, for and by parameters
# Resulting header would look like this:
#   forwarded: host="host.com";by=_haproxy;for="[::1]:10"
backend www_custom
    mode http
    option forwarded host-expr str(host.com) by-expr str(_haproxy) for for_port-expr int(10)

# Those servers want random 'for' obfuscated identifiers for request
# tracing purposes while protecting sensitive IP information
# Resulting header would look like this:
#   forwarded: for=_000000002B1F4D63
backend www_for_hide
    mode http
    option forwarded for-expr rand,hex
option forwardfor [ except <network> ] [ header <name> ] [ if-none ]
Enable insertion of the X-Forwarded-For header to requests sent to servers

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments :
<network> is an optional argument used to disable this option for sources
          matching <network>
<name>    an optional argument to specify a different "X-Forwarded-For"
          header name.
Since HAProxy works in reverse-proxy mode, the servers see its IP address as
their client address. This is sometimes annoying when the client's IP address
is expected in server logs. To solve this problem, the well-known HTTP header
"X-Forwarded-For" may be added by HAProxy to all requests sent to the server.
This header contains a value representing the client's IP address. Since this
header is always appended at the end of the existing header list, the server
must be configured to always use the last occurrence of this header only. See
the server's manual to find how to enable use of this standard header. Note
that only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.

The keyword "header" may be used to supply a different header name to replace
the default "X-Forwarded-For". This can be useful where you might already
have a "X-Forwarded-For" header from a different application (e.g. stunnel),
and you need preserve it. Also if your backend server doesn't use the
"X-Forwarded-For" header and requires different one (e.g. Zeus Web Servers
require "X-Cluster-Client-IP").

Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1. IPv4 and IPv6 are both supported.

Alternatively, the keyword "if-none" states that the header will only be
added if it is not present. This should only be used in perfectly trusted
environment, as this might cause a security issue if headers reaching HAProxy
are under the control of the end-user.

This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined. In the case of the "if-none" argument, if at least one of
the frontend or the backend does not specify it, it wants the addition to be
mandatory, so it wins.
Example :
# Public HTTP address also used by stunnel on the same machine
frontend www
    mode http
    option forwardfor except 127.0.0.1  # stunnel already adds the header

# Those servers want the IP Address in X-Client
backend www
    mode http
    option forwardfor header X-Client
Enable or disable the case adjustment of HTTP/1 headers sent to bogus clients

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

When HAProxy receives an HTTP/1 response, its header names are converted to
lower case and manipulated and sent this way to the clients. If a client is
known to violate the HTTP standards and to fail to process a response coming
from HAProxy, it is possible to transform the lower case header names to a
different format when the response is formatted and sent to the client, by
enabling this option and specifying the list of headers to be reformatted
using the global directives "h1-case-adjust" or "h1-case-adjust-file". This
must only be a temporary workaround for the time it takes the client to be
fixed, because clients which require such workarounds might be vulnerable to
content smuggling attacks and must absolutely be fixed.

Please note that this option will not affect standards-compliant clients.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable the case adjustment of HTTP/1 headers sent to bogus servers

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

When HAProxy receives an HTTP/1 request, its header names are converted to
lower case and manipulated and sent this way to the servers. If a server is
known to violate the HTTP standards and to fail to process a request coming
from HAProxy, it is possible to transform the lower case header names to a
different format when the request is formatted and sent to the server, by
enabling this option and specifying the list of headers to be reformatted
using the global directives "h1-case-adjust" or "h1-case-adjust-file". This
must only be a temporary workaround for the time it takes the server to be
fixed, because servers which require such workarounds might be vulnerable to
content smuggling attacks and must absolutely be fixed.

Please note that this option will not affect standards-compliant servers.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable waiting for whole HTTP request body before proceeding

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments : none
It is sometimes desirable to wait for the body of an HTTP request before
taking a decision. This is what is being done by "balance url_param" for
example. The first use case is to buffer requests from slow clients before
connecting to the server. Another use case consists in taking the routing
decision based on the request body's contents. This option placed in a
frontend or backend forces the HTTP processing to wait until either the whole
body is received or the request buffer is full. It can have undesired side
effects with some applications abusing HTTP by expecting unbuffered
transmissions between the frontend and the backend, so this should definitely
not be used by default.
Enable or disable logging of null connections and request timeouts

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
no
no
Arguments : none
Recently some browsers started to implement a "pre-connect" feature
consisting in speculatively connecting to some recently visited web sites
just in case the user would like to visit them. This results in many
connections being established to web sites, which end up in 408 Request
Timeout if the timeout strikes first, or 400 Bad Request when the browser
decides to close them first. These ones pollute the log and feed the error
counters. There was already "option dontlognull" but it's insufficient in
this case. Instead, this option does the following things :
   - prevent any 400/408 message from being sent to the client if nothing
     was received over a connection before it was closed;
   - prevent any log from being emitted in this situation;
   - prevent any error counter from being incremented

That way the empty connection is silently ignored. Note that it is better
not to use this unless it is clear that it is needed, because it will hide
real problems. The most common reason for not receiving a request and seeing
a 408 is due to an MTU inconsistency between the client and an intermediary
element such as a VPN, which blocks too large packets. These issues are
generally seen with POST requests as well as GET with large cookies. The logs
are often the only way to detect them.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Enable or disable HTTP keep-alive from client to server for HTTP/1.x
connections

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments : none
By default HAProxy operates in keep-alive mode with regards to persistent
HTTP/1.x connections: for each connection it processes each request and
response, and leaves the connection idle on both sides. This mode may be
changed by several options such as "option http-server-close" or "option
httpclose". This option allows to set back the keep-alive mode, which can be
useful when another mode was used in a defaults section.

Setting "option http-keep-alive" enables HTTP keep-alive mode on the client-
and server- sides. This provides the lowest latency on the client side (slow
network) and the fastest session reuse on the server side at the expense
of maintaining idle connections to the servers. In general, it is possible
with this option to achieve approximately twice the request rate that the
"http-server-close" option achieves on small objects. There are mainly two
situations where this option may be useful :

  - when the server is non-HTTP compliant and authenticates the connection
    instead of requests (e.g. NTLM authentication)

  - when the cost of establishing the connection to the server is significant
    compared to the cost of retrieving the associated object from the server.

This last case can happen when the server is a fast static server of cache.

At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "timeout http-keep-alive" or "timeout http-request" if
not set.

This option disables and replaces any previous "option httpclose" or "option
http-server-close".
Instruct the system to favor low interactive delays over performance in HTTP

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes
Arguments : none
In HTTP, each payload is unidirectional and has no notion of interactivity.
Any agent is expected to queue data somewhat for a reasonably low delay.
There are some very rare server-to-server applications that abuse the HTTP
protocol and expect the payload phase to be highly interactive, with many
interleaved data chunks in both directions within a single request. This is
absolutely not supported by the HTTP specification and will not work across
most proxies or servers. When such applications attempt to do this through
HAProxy, it works but they will experience high delays due to the network
optimizations which favor performance by instructing the system to wait for
enough data to be available in order to only send full packets. Typical
delays are around 200 ms per round trip. Note that this only happens with
abnormal uses. Normal uses such as CONNECT requests nor WebSockets are not
affected.

When "option http-no-delay" is present in either the frontend or the backend
used by a connection, all such optimizations will be disabled in order to
make the exchanges as fast as possible. Of course this offers no guarantee on
the functionality, as it may break at any other place. But if it works via
HAProxy, it will work as fast as possible. This option should never be used
by default, and should never be used at all unless such a buggy application
is discovered. The impact of using this option is an increase of bandwidth
usage and CPU usage, which may significantly lower performance in high
latency environments.
Define whether HAProxy will announce keepalive for HTTP/1.x connection to the
server or not

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
no
no
yes
yes
yes
yes
Arguments : none
When running with "option http-server-close" or "option httpclose", HAProxy
adds a "Connection: close" header to the HTTP/1.x request forwarded to the
server. Unfortunately, when some servers see this header, they automatically
refrain from using the chunked encoding for responses of unknown length,
while this is totally unrelated. The effect is that a client or a cache could
receive an incomplete response without being aware of it, and consider the
response complete.

By setting "option http-pretend-keepalive", HAProxy will make the server
believe it will keep the connection alive. The server will then not fall back
to the abnormal undesired above. When HAProxy gets the whole response, it
will close the connection with the server just as it would do with the
"option httpclose". That way the client gets a normal response and the
connection is correctly closed on the server side.

It is recommended not to enable this option by default, because most servers
will more efficiently close the connection themselves after the last packet,
and release its buffers slightly earlier. Also, the added packet on the
network could slightly reduce the overall peak performance. However it is
worth noting that when this option is enabled, HAProxy will have slightly
less work to do. So if HAProxy is the bottleneck on the whole architecture,
enabling this option might save a few CPU cycles.

This option may be set in backend and listen sections. Using it in a frontend
section will be ignored and a warning will be reported during startup. It is
a backend related option, so there is no real reason to set it on a
frontend.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
option http-restrict-req-hdr-names { preserve | delete | reject }
Set HAProxy policy about HTTP request header names containing characters
outside the "[a-zA-Z0-9-]" charset

May be used in the following contexts: http

May be used in sections :

defaultsfrontendlistenbackend
yes
yes
yes
yes
yes
yes
yes
yes