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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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.

The HTTP protocol is transaction-driven. This means that each request will lead
to one and only one response. Traditionally, a TCP connection is established
from the client to the server, a request is sent by the client through the
connection, the server responds, and the connection is closed. A new request
will involve a new connection :

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

In this mode, 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.

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 :

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

Its advantages are a reduced latency between transactions, and less processing
power required on the server side. It is generally better than the close mode,
but not always because the clients often limit their concurrent connections to
a smaller value.

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.

The next improvement is the multiplexed mode, as implemented in HTTP/2. This
time, each transaction is assigned a single stream identifier, and all streams
are multiplexed over an existing connection. Many requests can be sent in
parallel by the client, and responses can arrive in any order since they also
carry the stream identifier.

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 supports 5 connection modes :
  - keep alive    : all requests and responses are processed (default)
  - tunnel        : only the first request and response are processed,
                    everything else is forwarded with no analysis.
  - passive close : tunnel with "Connection: close" added in both directions.
  - server close  : the server-facing connection is closed after the response.
  - forced close  : the connection is actively closed after end of response.

For HTTP/2, the connection mode resembles more the "server close" mode : given
the independence of all streams, there is currently no place to hook the idle
server connection after a response, so it is closed after the response. HTTP/2
is only supported for incoming connections, not on connections going to
servers.

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

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/2 doesn't 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").
However, haproxy natively processes HTTP/1.x requests and headers, so requests
received over an HTTP/2 connection are transcoded to HTTP/1.1 before being
processed. This explains why they still appear as "HTTP/1.1" in haproxy's logs
as well as in server logs.

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 1.2, lines 4 and 5
define a total of 3 values for the "Accept:" header.

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, header names are always sent in lower case,
as can be seen when running in debug mode.

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.

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 are HTTP/1.1 only). 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.

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)

Please refer to RFC7231 for the detailed meaning of all such codes. 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".

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 "block" ACL or "reqdeny" filter
   408  when the request timeout strikes before the request is complete
   500  when haproxy encounters an unrecoverable internal error, such as a
        memory allocation failure, which should never happen
   502  when the server returns an empty, invalid or incomplete response, or
        when an "rspdeny" filter 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).

Response headers work exactly like request headers, and as such, HAProxy uses
the same parsing function for both. Please refer to paragraph 1.2.2 for more
details.

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

  - the arguments from the command-line, which always take precedence
  - the "global" section, which sets process-wide parameters
  - the proxies sections which can take form of "defaults", "listen",
    "frontend" and "backend".

The configuration file syntax consists in lines beginning with a keyword
referenced in this manual, optionally followed by one or several parameters
delimited by spaces.

HAProxy's configuration introduces a quoting and escaping system similar to
many programming languages. The configuration file supports 3 types: escaping
with a backslash, weak quoting with double quotes, and strong quoting with
single quotes.

If spaces have to be entered in strings, then they must be escaped by preceding
them by a backslash ('\') or by quoting them. Backslashes also have to be
escaped by doubling or strong quoting them.

Escaping 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

Weak quoting is achieved by using double quotes (""). Weak quoting prevents
the interpretation of:

       space as a parameter separator
  '    single quote as a strong quoting delimiter
  #    hash as a comment start

Weak quoting permits the interpretation of variables, if you want to use a non
-interpreted dollar within a double quoted string, you should escape it with a
backslash ("\$"), it does not work outside weak quoting.

Interpretation of escaping and special characters are not prevented by weak
quoting.

Strong quoting is achieved by using single quotes (''). Inside single quotes,
nothing is interpreted, it's the efficient way to quote regexes.

Quoted and escaped strings are replaced in memory by their interpreted
equivalent, it allows you to perform concatenation.

# those are equivalents:
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

# those are equivalents:
reqrep "^([^\ :]*)\ /static/(.*)"     \1\ /\2
reqrep "^([^ :]*)\ /static/(.*)"     '\1 /\2'
reqrep "^([^ :]*)\ /static/(.*)"     "\1 /\2"
reqrep "^([^ :]*)\ /static/(.*)"     "\1\ /\2"

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.

bind "fd@${FD_APP1}"

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

user "$HAPROXY_USER"

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

    # 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
   - ca-base
   - chroot
   - crt-base
   - cpu-map
   - daemon
   - description
   - deviceatlas-json-file
   - deviceatlas-log-level
   - deviceatlas-separator
   - deviceatlas-properties-cookie
   - external-check
   - gid
   - group
   - hard-stop-after
   - log
   - log-tag
   - log-send-hostname
   - lua-load
   - nbproc
   - nbthread
   - node
   - pidfile
   - presetenv
   - resetenv
   - uid
   - ulimit-n
   - user
   - setenv
   - stats
   - ssl-default-bind-ciphers
   - ssl-default-bind-ciphersuites
   - ssl-default-bind-options
   - ssl-default-server-ciphers
   - ssl-default-server-ciphersuites
   - ssl-default-server-options
   - ssl-dh-param-file
   - ssl-server-verify
   - unix-bind
   - unsetenv
   - 51degrees-data-file
   - 51degrees-property-name-list
   - 51degrees-property-separator
   - 51degrees-cache-size
   - wurfl-data-file
   - wurfl-information-list
   - wurfl-information-list-separator
   - wurfl-engine-mode
   - wurfl-cache-size
   - wurfl-useragent-priority

 * Performance tuning
   - max-spread-checks
   - maxconn
   - maxconnrate
   - maxcomprate
   - maxcompcpuusage
   - maxpipes
   - maxsessrate
   - maxsslconn
   - maxsslrate
   - maxzlibmem
   - noepoll
   - nokqueue
   - nopoll
   - nosplice
   - nogetaddrinfo
   - noreuseport
   - spread-checks
   - server-state-base
   - server-state-file
   - ssl-engine
   - ssl-mode-async
   - tune.buffers.limit
   - tune.buffers.reserve
   - tune.bufsize
   - tune.chksize
   - tune.comp.maxlevel
   - tune.h2.header-table-size
   - tune.h2.initial-window-size
   - tune.h2.max-concurrent-streams
   - tune.http.cookielen
   - tune.http.logurilen
   - tune.http.maxhdr
   - tune.idletimer
   - tune.lua.forced-yield
   - tune.lua.maxmem
   - tune.lua.session-timeout
   - tune.lua.task-timeout
   - tune.lua.service-timeout
   - tune.maxaccept
   - tune.maxpollevents
   - tune.maxrewrite
   - tune.pattern.cache-size
   - tune.pipesize
   - tune.rcvbuf.client
   - tune.rcvbuf.server
   - tune.recv_enough
   - tune.sndbuf.client
   - tune.sndbuf.server
   - tune.ssl.cachesize
   - tune.ssl.lifetime
   - tune.ssl.force-private-cache
   - tune.ssl.maxrecord
   - tune.ssl.default-dh-param
   - tune.ssl.ssl-ctx-cache-size
   - tune.ssl.capture-cipherlist-size
   - 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
   - debug
   - quiet

Assigns a default directory to fetch SSL CA certificates and CRLs from when a
relative path is used with "ca-file
This keyword is available in sections :
Bind options
Server and default-server options" or "crl-file
This keyword is available in sections :
Bind options
Server and default-server options" directives. Absolute
locations specified in "ca-file
This keyword is available in sections :
Bind options
Server and default-server options" and "crl-file
This keyword is available in sections :
Bind options
Server and default-server options" prevail and ignore "ca-base".

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.

On Linux 2.6 and above, it is possible to bind a process or a thread to a
specific CPU set. This means that the process or the thread will never run on
other CPUs. The "cpu-map" directive specifies CPU sets for process or thread
sets. The first argument is a process set, eventually followed by a thread
set. These sets have the 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 process IDs above nbproc and any thread IDs above nbthread are
ignored. It is possible to specify a range with two such number delimited by
a dash ('-'). It also is possible to specify all processes at once using
"all", only odd numbers using "odd" or even numbers using "even", just like
with the "bind-process" directive. The second and forthcoming arguments are
CPU sets. Each CPU set is either a unique number between 0 and 31 or 63 or a
range with two such numbers delimited by a dash ('-'). Multiple CPU numbers
or ranges may be specified, and the processes or threads will be allowed to
bind to all of them. Obviously, multiple "cpu-map" directives may be
specified. Each "cpu-map" directive will replace the previous ones when they
overlap. A thread will be bound on the intersection of its mapping and the
one of the process on which it is attached. If the intersection is null, no
specific binding will be set for the thread.

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 process set to let HAProxy
automatically bind a process or a thread to a CPU by incrementing
process/thread 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 a process and a thread range with the
"auto:" prefix is not supported. Only one range is supported, the other one
must be a fixed number.

cpu-map 1-4 0-3   # bind processes 1 to 4 on the first 4 CPUs

cpu-map 1/all 0-3 # bind all threads of the first process on the
                  # first 4 CPUs

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

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

# all these lines bind the 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

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

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

# invalid cpu-map because automatic binding is used with a process range
# and a thread range.
cpu-map auto:all/all   0 # invalid
cpu-map auto:all/1-4   0 # invalid
cpu-map auto:1-4/all   0 # invalid

Assigns a default directory to fetch SSL certificates from when a relative
path is used with "crtfile" directives. Absolute locations specified after
"crtfile" 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.

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 character separator for the API properties results. This directive
is optional and set to | 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.

Allows the use of an external agent to perform health checks.
This is disabled by default as a security precaution.
See "option external-check".

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
This keyword is available in sections :
Process management and security
Userlists
Bind options" and "uid
This keyword is available in sections :
Process management and security
Bind options".

Defines the maximum time allowed to perform a clean soft-stop.

<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.

global
  hard-stop-after 30s

Similar to "gid
This keyword is available in sections :
Process management and security
Bind options" but uses the GID of group name <group name> from /etc/group.
See also "gid
This keyword is available in sections :
Process management and security
Bind options" and "user
This keyword is available in sections :
Process management and security
Userlists
Bind options".

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".

<address> 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).

      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.

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

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

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

<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

An optional level can be specified to filter outgoing messages. By default,
all messages are sent. If a maximum 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

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.

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
This keyword is available in sections :
Process management and security
Alphabetically sorted keywords reference" directive.

This global directive loads and executes a Lua file. This directive can be
used multiple times.

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. It is recommended to use this mode with multiprocess and
systemd.
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.

Creates <number> processes when going daemon. This requires the "daemon"
mode. By default, only one process is created, which is the recommended mode
of operation. For systems limited to small sets of file descriptors per
process, it may be needed to fork multiple daemons. USING MULTIPLE PROCESSES
IS HARDER TO DEBUG AND IS REALLY DISCOURAGED. See also "daemon" and
"nbthread".

This setting is only available when support for threads was built in. It
creates <number> threads for each created processes. It means if HAProxy is
started in foreground, it only creates <number> threads for the first
process. See also "nbproc
This keyword is available in sections :
Process management and security
Fetching samples from internal states".

Writes PIDs of all daemons into file <pidfile>. This option is equivalent to
the "-p" command line argument. The file must be accessible to the user
starting the process. See also "daemon".

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".

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".

Limits the stats socket to a certain set of processes numbers. By default the
stats socket is bound to all processes, causing a warning to be emitted when
nbproc is greater than 1 because there is no way to select the target process
when connecting. However, by using this setting, it becomes possible to pin
the stats socket to a specific set of processes, typically the first one. The
warning will automatically be disabled when this setting is used, whatever
the number of processes used. The maximum process ID depends on the machine's
word size (32 or 64). Ranges can be partially defined. The higher bound can
be omitted. In such case, it is replaced by the corresponding maximum
value. A better option consists in using the "process" setting of the "stats
socket" line to force the process on each line.

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"

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
This keyword is available in sections :
Bind options
Server and default-server options". 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
default ssl-options to force on all "bind" lines. Please check the "bind"
keyword to see available options.

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 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
This keyword is available in sections :
Bind options
Server and default-server options". 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
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 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, pre-generated DH parameters of the size
specified by tune.ssl.default-dh-param 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.

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'.

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.

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 }.

By default, the stats socket is limited to 10 concurrent connections. It is
possible to change this value with "stats maxconn".

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
This keyword is available in sections :
Process management and security
Bind options" and "user
This keyword is available in sections :
Process management and security
Userlists
Bind options".

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.

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.

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".

Similar to "uid
This keyword is available in sections :
Process management and security
Bind options" but uses the UID of user name <user name> from /etc/passwd.
See also "uid
This keyword is available in sections :
Process management and security
Bind options" and "group
This keyword is available in sections :
Process management and security
Userlists
Bind options".

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.

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.

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.

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.

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_engine_target         Contains a string representing the currently
                              set WURFL Engine Target. Possible values are
                              "HIGH_ACCURACY", "HIGH_PERFORMANCE", "INVALID".

- 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.

- wurfl_useragent_priority    The user agent priority used by WURFL.

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.

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.

Sets the WURFL engine target. You can choose between 'accuracy' or
'performance' targets. In performance mode, desktop web browser detection is
done programmatically without referencing the WURFL data. As a result, most
desktop web browsers are returned as generic_web_browser WURFL ID for
performance. If either performance or accuracy are not defined, performance
mode is enabled by default.

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

Sets the WURFL caching strategy. Here <U> is the Useragent cache size, and
<D> is the internal device cache size. There are three possibilities here :
- "0"     : no cache is used.
- <U>     : the Single LRU cache is used, the size is expressed in elements.
- <U>,<D> : the Double LRU cache is used, both sizes are in elements. This is
            the highest performing option.

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

Tells WURFL if it should prioritize use of the plain user agent ('plain')
over the default sideloaded browser user agent ('sideloaded_browser').

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

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 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 default to the value
set in DEFAULT_MAXCONN at build time (reported in haproxy -vv) if no memory
limit is enforced, or will be computed based on the memory limit, 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).

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.

Sets the maximum per-process input compression rate to <number> kilobytes
per second. For each session, if the maximum is reached, the compression
level will be decreased during the session. If the maximum is reached at the
beginning of a session, the session 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.

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. In
case of multiple processes (nbproc > 1), each process manages its individual
usage. 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.

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.

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.

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).

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.

Sets the maximum amount of RAM in megabytes per process usable by the zlib.
When the maximum amount is reached, future sessions 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 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 "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" and "noepoll".

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".

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 SO_REUSEPORT - see socket(7). It is equivalent to the
command line argument "-dR".

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.

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

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 reneg
handshakes).

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, sessions which need a buffer wait for
another one to be released by another session. 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.

Sets the buffer size to this size (in bytes). Lower values allow more
sessions 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).

Sets the check buffer size to this size (in bytes). Higher values may help
find string or regex patterns in very large pages, though doing so may imply
more memory and CPU usage. The default value is 16384 and can be changed at
build time. It is not recommended to change this value, but to use better
checks whenever possible.

Sets the maximum compression level. The compression level affects CPU
usage during compression. This value affects CPU usage during compression.
Each session using compression initializes the compression algorithm with
this value. The default value is 1.

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 HTTP/2 initial window size, 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.
The default value is 65535, which roughly allows up to 5 Mbps of upload
bandwidth per client over a network showing a 100 ms ping time, or 500 Mbps
over a 1-ms local network. It can make sense to increase this value to allow
faster uploads, or to reduce it to increase fairness when dealing with many
clients. It doesn't affect resource usage.

Sets the HTTP/2 maximum number of concurrent streams per connection (ie the
number of outstanding requests on a single connection). The default value is
100. A larger one may slightly improve page load time for complex sites when
visited over high latency networks, but increases the amount of resources a
single client may allocate. 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 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 session, so don't push this limit too high.

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 not reason for changing this value. Please check
tune.ssl.maxrecord below.

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.

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.

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.

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
give better performance at high connection rates. However in multi-process
modes, keeping a bit of fairness between processes generally is better to
increase performance. 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 64. 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 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 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.

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 autotune 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.

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 autotune 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. 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
and are shared between all processes if "nbproc
This keyword is available in sections :
Process management and security
Fetching samples from internal states" is greater than 1. Setting
this value to 0 disables the SSL session cache.

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 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 a time. 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).

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. Default value if 1024. 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.

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 size of the buffer used for capturing client-hello cipher
list. If the value is 0 (default value) the capture is disabled, otherwise
a buffer is allocated for each SSL/TLS connection.

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 session. 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 session. 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.

Enables debug mode which dumps to stdout all exchanges, and disables forking
into background. It is the equivalent of the command-line argument "-d". It
should never be used in a production configuration since it may prevent full
system startup.

Do not display any message during startup. It is equivalent to the command-
line argument "-q".

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.

Creates new userlist with name <listname>. Many independent userlists can be
used to store authentication & authorization data for independent customers.

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.

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!

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.

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. 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.

Creates a new peer list with name <peersect>. It is an independent section,
which is referenced by one or more stick-tables.

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.

This re-enables a peers section which was previously disabled via the
"disabled
This keyword is available in sections :
Peers
Alphabetically sorted keywords reference
Server and default-server options" keyword.

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), haproxy will listen for incoming remote peer
connection on <ip>:<port>. Otherwise, <ip>:<port> defines where to connect to
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 <ip>:<port> 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 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.

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

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.

Creates a new mailer list with the name <mailersect>. It is an
independent section which is referenced by one or more proxies.

Defines a mailer inside a mailers section.

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.

mailers mymailers
    timeout mail 20s
    mailer smtp1 192.168.0.1:587

Proxy configuration can be located in a set of sections :
 - defaults [<name>]
 - frontend <name>
 - backend  <name>
 - listen   <name>

A "defaults" section sets default parameters for all other sections following
its declaration. Those default parameters are reset by the next "defaults"
section. See below for the list of parameters which can be set in a "defaults"
section. The name is optional but its use is encouraged for better readability.

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.

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 5 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.

  - TUN: tunnel ("option http-tunnel") : this was the default mode for versions
    1.0 to 1.5-dev21 : only the first request and response are processed, and
    everything else is forwarded with no analysis at all. This mode should not
    be used as it creates lots of trouble with logging and HTTP processing.

  - PCL: passive close ("option httpclose") : exactly the same as tunnel mode,
    but with "Connection: close" appended in both directions to try to make
    both ends close after the first request/response exchange.

  - 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.

  - FCL: forced close ("option forceclose") : the connection is actively closed
    after the end of the response.

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 force close is the strongest.

                          Backend mode

                | KAL | TUN | PCL | SCL | FCL
            ----+-----+-----+-----+-----+----
            KAL | KAL | TUN | PCL | SCL | FCL
            ----+-----+-----+-----+-----+----
            TUN | TUN | TUN | PCL | SCL | FCL
 Frontend   ----+-----+-----+-----+-----+----
   mode     PCL | PCL | PCL | PCL | FCL | FCL
            ----+-----+-----+-----+-----+----
            SCL | SCL | SCL | FCL | SCL | FCL
            ----+-----+-----+-----+-----+----
            FCL | FCL | FCL | FCL | FCL | FCL

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.

keyword	defaults	frontend	listen	backend
acl
appsession
backlog
balance
bind
bind-process
(deprecated)block
capture cookie
capture request header
capture response header
(deprecated)clitimeout
compression
(deprecated)contimeout
cookie
declare capture
default-server
default_backend
description
disabled
dispatch
keyword	defaults	frontend	listen	backend
email-alert from
email-alert level
email-alert mailers
email-alert myhostname
email-alert to
enabled
errorfile
errorloc
errorloc302
errorloc303
force-persist
filter
fullconn
grace
hash-type
http-check disable-on-404
http-check expect
http-check send-state
http-request
http-response
keyword	defaults	frontend	listen	backend
http-reuse
http-send-name-header
id
ignore-persist
load-server-state-from-file
(*)log
log-format
log-format-sd
log-tag
max-keep-alive-queue
maxconn
mode
monitor fail
monitor-net
monitor-uri
(*)option abortonclose
(*)option accept-invalid-http-request
(*)option accept-invalid-http-response
(*)option allbackups
(*)option checkcache
keyword	defaults	frontend	listen	backend
(*)option clitcpka
(*)option contstats
(*)option dontlog-normal
(*)option dontlognull
(*)option forceclose
option forwardfor
(*)option http-buffer-request
(*)option http-ignore-probes
(*)option http-keep-alive
(*)option http-no-delay
(*)option http-pretend-keepalive
(*)option http-server-close
(*)option http-tunnel
(*)option http-use-proxy-header
option httpchk
(*)option httpclose
option httplog
(*)option http_proxy
(*)option independent-streams
option ldap-check
keyword	defaults	frontend	listen	backend
option external-check
(*)option log-health-checks
(*)option log-separate-errors
(*)option logasap
option mysql-check
(*)option nolinger
option originalto
(*)option persist
option pgsql-check
(*)option prefer-last-server
(*)option redispatch
option redis-check
option smtpchk
(*)option socket-stats
(*)option splice-auto
(*)option splice-request
(*)option splice-response
option spop-check
(*)option srvtcpka
option ssl-hello-chk
keyword	defaults	frontend	listen	backend
option tcp-check
(*)option tcp-smart-accept
(*)option tcp-smart-connect
option tcpka
option tcplog
(*)option transparent
external-check command
external-check path
persist rdp-cookie
rate-limit sessions
redirect
(deprecated)redisp
(deprecated)redispatch
reqadd
reqallow
reqdel
reqdeny
reqiallow
reqidel
reqideny
keyword	defaults	frontend	listen	backend
reqipass
reqirep
reqitarpit
reqpass
reqrep
reqtarpit
retries
rspadd
rspdel
rspdeny
rspidel
rspideny
rspirep
rsprep
server
server-state-file-name
server-template
source
(deprecated)srvtimeout
stats admin
keyword	defaults	frontend	listen	backend
stats auth
stats enable
stats hide-version
stats http-request
stats realm
stats refresh
stats scope
stats show-desc
stats show-legends
stats show-node
stats uri
stick match
stick on
stick store-request
stick store-response
stick-table
tcp-check connect
tcp-check expect
tcp-check send
tcp-check send-binary
keyword	defaults	frontend	listen	backend
tcp-request connection
tcp-request content
tcp-request inspect-delay
tcp-request session
tcp-response content
tcp-response inspect-delay
timeout check
timeout client
timeout client-fin
(deprecated)timeout clitimeout
timeout connect
(deprecated)timeout contimeout
timeout http-keep-alive
timeout http-request
timeout queue
timeout server
timeout server-fin
(deprecated)timeout srvtimeout
timeout tarpit
timeout tunnel
keyword	defaults	frontend	listen	backend
(deprecated)transparent
unique-id-format
unique-id-header
use_backend
use-server

This section provides a description of each keyword and its usage.

Declare or complete an access list.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

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.

Define session stickiness on an existing application cookie.

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

<cookie>   this is the name of the cookie used by the application and which
           HAProxy will have to learn for each new session.

<length>   this is the max number of characters that will be memorized and
           checked in each cookie value.

<holdtime> this is the time after which the cookie will be removed from
           memory if unused. If no unit is specified, this time is in
           milliseconds.

request-learn
           If this option is specified, then haproxy will be able to learn
           the cookie found in the request in case the server does not
           specify any in response. This is typically what happens with
           PHPSESSID cookies, or when haproxy's session expires before
           the application's session and the correct server is selected.
           It is recommended to specify this option to improve reliability.

prefix     When this option is specified, haproxy will match on the cookie
           prefix (or URL parameter prefix). The appsession value is the
           data following this prefix.

           Example :
           appsession ASPSESSIONID len 64 timeout 3h prefix

           This will match the cookie ASPSESSIONIDXXX=XXXX,
           the appsession value will be XXX=XXXX.

mode       This option allows to change the URL parser mode.
           2 modes are currently supported :
           - path-parameters :
             The parser looks for the appsession in the path parameters
             part (each parameter is separated by a semi-colon), which is
             convenient for JSESSIONID for example.
             This is the default mode if the option is not set.
           - query-string :
             In this mode, the parser will look for the appsession in the
             query string.

As of version 1.6, appsessions was removed. It is more flexible and more
convenient to use stick-tables instead, and stick-tables support multi-master
replication and data conservation across reloads, which appsessions did not.

Give hints to the system about the approximate listen backlog desired size

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

<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.

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).

Define the load balancing algorithm to be used in a backend.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

<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.

  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%).

  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.

  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
This keyword is available in sections :
Alphabetically sorted keywords reference
Bind options
Server and default-server options"), 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.

  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".

  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.

  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".

  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".

  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 rdp_cookie pattern fetch function.

<arguments> is an optional list of arguments which may be needed by some
            algorithms. Right now, only "url_param" and "uri" 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.

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

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

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 reqideny 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.

Define one or several listening addresses and/or ports in a frontend.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

<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 '::'.
              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
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only).
                  Note: since abstract sockets are not "rebindable", they
                        do not cope well with multi-process mode during
                        soft-restart, so it is better to avoid them if
                        nbproc is greater than 1. The effect is that if the
                        new process fails to start, only one of the old ones
                        will be able to rebind to the socket.
                - 'fd@<n>' -> use file descriptor <n> inherited from the
                  parent. The fd must be bound and may or may not already
                  be listening.
              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.

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}"

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.

Limit visibility of an instance to a certain set of processes numbers.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

all           All process will see this instance. This is the default. It
              may be used to override a default value.

odd           This instance will be enabled on processes 1,3,5,...63. This
              option may be combined with other numbers.

even          This instance will be enabled on processes 2,4,6,...64. This
              option may be combined with other numbers. Do not use it
              with less than 2 processes otherwise some instances might be
              missing from all processes.

process_num   The instance will be enabled on this process number or range,
              whose values must all be between 1 and 32 or 64 depending on
              the machine's word size. Ranges can be partially defined. The
              higher bound can be omitted. In such case, it is replaced by
              the corresponding maximum value. If a proxy is bound to
              process numbers greater than the configured global.nbproc, it
              will either be forced to process #1 if a single process was
              specified, or to all processes otherwise.

This keyword limits binding of certain instances to certain processes. This
is useful in order not to have too many processes listening to the same
ports. For instance, on a dual-core machine, it might make sense to set
'nbproc 2' in the global section, then distributes the listeners among 'odd'
and 'even' instances.

At the moment, it is not possible to reference more than 32 or 64 processes
using this keyword, but this should be more than enough for most setups.
Please note that 'all' really means all processes regardless of the machine's
word size, and is not limited to the first 32 or 64.

Each "bind" line may further be limited to a subset of the proxy's processes,
please consult the "process" bind keyword in section 5.1.

When a frontend has no explicit "bind-process" line, it tries to bind to all
the processes referenced by its "bind" lines. That means that frontends can
easily adapt to their listeners' processes.

If some backends are referenced by frontends bound to other processes, the
backend automatically inherits the frontend's processes.

listen app_ip1
    bind 10.0.0.1:80
    bind-process odd

listen app_ip2
    bind 10.0.0.2:80
    bind-process even

listen management
    bind 10.0.0.3:80
    bind-process 1 2 3 4

listen management
    bind 10.0.0.4:80
    bind-process 1-4

Block a layer 7 request if/unless a condition is matched

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

The HTTP request will be blocked very early in the layer 7 processing
if/unless <condition> is matched. A 403 error will be returned if the request
is blocked. The condition has to reference ACLs (see section 7). This is
typically used to deny access to certain sensitive resources if some
conditions are met or not met. There is no fixed limit to the number of
"block" statements per instance. To block connections at layer 4 (without
sending a 403 error) see "tcp-request connection reject" and
"tcp-request content reject" rules.

This form is deprecated, do not use it in any new configuration, use the new
"http-request deny" instead.

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
# block is deprecated. Use http-request deny instead:
#block if invalid_src || local_dst
http-request deny if invalid_src || local_dst

Capture and log a cookie in the request and in the response.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

<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
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options
Fetching HTTP samples (Layer 7)" 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.

capture cookie ASPSESSION len 32

Capture and log the last occurrence of the specified request header.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

<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 session.
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.

capture request header Host len 15
capture request header X-Forwarded-For len 15
capture request header Referer len 15

Capture and log the last occurrence of the specified response header.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

<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 session.
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.

capture response header Content-length len 9
capture response header Location len 15

Set the maximum inactivity time on the client side.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

<timeout> is the timeout value is 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 inactivity timeout applies when the client is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase, when the client sends the request, and during the
response while it is reading data sent by the server. The value is specified
in milliseconds by default, but can be in any other unit if the number is
suffixed by the unit, as specified at the top of this document. In TCP mode
(and to a lesser extent, in HTTP mode), it is highly recommended that the
client timeout remains equal to the server timeout in order to avoid complex
situations to debug. It is a good practice to cover one or several TCP packet
losses by specifying timeouts that are slightly above multiples of 3 seconds
(e.g. 4 or 5 seconds).

This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of expired sessions in
the system if the system's timeouts are not configured either.

This parameter is provided for compatibility but is currently deprecated.
Please use "timeout client" instead.

Enable HTTP compression.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

algo     is followed by the list of supported compression algorithms.
type     is followed by the list of MIME types that will be compressed.
offload  makes haproxy work as a compression offloader only (see notes).

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.

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. Note: for now, the "offload" setting is
ignored when set in a defaults section.

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
  * HTTP status code is not 200
  * response header "Transfer-Encoding" contains "chunked" (Temporary
    Workaround)
  * 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)

Note: The compression does not rewrite Etag headers, and does not emit the
      Warning header.

compression algo gzip
compression type text/html text/plain

Set the maximum time to wait for a connection attempt to a server to succeed.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

<timeout> is the timeout value is 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.

If the server is located on the same LAN as haproxy, the connection should be
immediate (less than a few milliseconds). Anyway, it is a good practice to
cover one or several TCP packet losses by specifying timeouts that are
slightly above multiples of 3 seconds (e.g. 4 or 5 seconds). By default, the
connect timeout also presets the queue timeout to the same value if this one
has not been specified. Historically, the contimeout was also used to set the
tarpit timeout in a listen section, which is not possible in a pure frontend.

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of failed sessions in
the system if the system's timeouts are not configured either.

This parameter is provided for backwards compatibility but is currently
deprecated. Please use "timeout connect", "timeout queue" or "timeout tarpit"
instead.

Enable cookie-based persistence in a backend.

May be used in sections :

defaults	frontend	listen	backend
yes	no	yes	yes

<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
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options
Fetching HTTP samples (Layer 7)" keyword in a "server" statement. If no cookie
is declared for a given server, the cookie is not set.

cookie JSESSIONID prefix
cookie SRV insert indirect nocache
cookie SRV insert postonly indirect
cookie SRV insert indirect nocache maxidle 30m maxlife 8h

Declares a capture slot.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	no

<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 sections :

defaults	frontend	listen	backend
yes	no	yes	yes

<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.

default-server inter 1000 weight 13

Specify the backend to use when no "use_backend" rule has been matched.

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	no

<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.

use_backend     dynamic  if  url_dyn
use_backend     static   if  url_css url_img extension_img
default_backend dynamic

Describe a listen, frontend or backend.

May be used in sections :

defaults	frontend	listen	backend
no	yes	yes	yes

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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

The "disabled
This keyword is available in sections :
Peers
Alphabetically sorted keywords reference
Server and default-server options" 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
This keyword is available in sections :
Peers
Alphabetically sorted keywords reference
Server and default-server options"
keyword in a "defaults" section.

Set a default server address

May be used in sections :

defaults	frontend	listen	backend
no	no	yes	yes

<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 sections :

defaults	frontend	listen	backend
yes	no	yes	yes

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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

The "enabled
This keyword is available in sections :
Peers
Alphabetically sorted keywords reference
Server and default-server options" keyword is used to explicitly enable an instance, when the
defaults has been set to "disabled
This keyword is available in sections :
Peers
Alphabetically sorted keywords reference
Server and default-server options". This is very rarely used.

Return a file contents instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 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 returned verbatim on the TCP socket. This allows any trick such
as redirections to another URL or site, as well as tricks to clean cookies,
force enable or disable caching, etc... The package provides default error
files returning the same contents as default errors.

The files should not exceed the configured buffer size (BUFSIZE), which
generally is 8 or 16 kB, otherwise they will be truncated. 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. For better HTTP compliance, it is
recommended that all header lines end with CR-LF and not LF alone.

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.

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

Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 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.

Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 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.

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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<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

Declare the mailers to be used when sending email alerts

May be used in sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<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.

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 sections :

defaults	frontend	listen	backend
yes	yes	yes	yes

<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.