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[DOC] summarize and highlight persistent connections behaviour

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(cherry picked from commit 3b5911a2d7cc61bc586259e12b3f38fd39d3a478)
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Patrick Mezard 2010-06-12 17:02:45 +02:00 committed by Willy Tarreau
parent 105facad12
commit 9ec2ec4085
1 changed files with 35 additions and 26 deletions
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doc/configuration.txt
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@ -127,8 +127,7 @@ header is used: "Content-length". This mode is called the "keep-alive" mode :
Its advantages are a reduced latency between transactions, and less processing 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, 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 but not always because the clients often limit their concurrent connections to
a smaller value. HAProxy currently only supports the HTTP keep-alive mode on a smaller value.
the client side, and transforms it to a close mode on the server side.
A last improvement in the communications is the pipelining mode. It still uses A last 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 keep-alive, but the client does not wait for the first response to send the
@ -142,8 +141,17 @@ latency is eliminated between subsequent requests. Many HTTP agents do not
correctly support pipelining since there is no way to associate a response with 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 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. server to reply in the exact same order as the requests were received.
HAProxy supports pipelined requests on the client side and processes them one
at a time. By default HAProxy operates in a tunnel-like mode with regards to persistent
connections: for each connection it processes the first request and forwards
everything else (including additional requests) to selected server. Once
established, the connection is persisted both on the client and server
sides. Use "option http-server-close" to preserve client persistent connections
while handling every incoming request individually, dispatching them one after
another to servers, in HTTP close mode. Use "option httpclose" to switch both
sides to HTTP close mode. "option forceclose" and "option
http-pretend-keepalive" help working around servers misbehaving in HTTP close
mode.
1.2. HTTP request 1.2. HTTP request
@ -2793,16 +2801,18 @@ no option http-server-close
yes | yes | yes | yes yes | yes | yes | yes
Arguments : none Arguments : none
This mode enables HTTP connection-close mode on the server side while keeping By default, when a client communicates with a server, HAProxy will only
the ability to support HTTP keep-alive and pipelining on the client side. analyze, log, and process the first request of each connection. Setting
This provides the lowest latency on the client side (slow network) and the "option http-server-close" enables HTTP connection-close mode on the server
fastest session reuse on the server side to save server resources, similarly side while keeping the ability to support HTTP keep-alive and pipelining on
to "option forceclose". It also permits non-keepalive capable servers to be the client side. This provides the lowest latency on the client side (slow
served in keep-alive mode to the clients if they conform to the requirements network) and the fastest session reuse on the server side to save server
of RFC2616. Please note that some servers do not always conform to those resources, similarly to "option forceclose". It also permits non-keepalive
requirements when they see "Connection: close" in the request. The effect capable servers to be served in keep-alive mode to the clients if they
will be that keep-alive will never be used. A workaround consists in enabling conform to the requirements of RFC2616. Please note that some servers do not
"option http-pretend-keepalive". always conform to those requirements when they see "Connection: close" in the
request. The effect will be that keep-alive will never be used. A workaround
consists in enabling "option http-pretend-keepalive".
At the moment, logs will not indicate whether requests came from the same At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end session or not. The accept date reported in the logs corresponds to the end
@ -2820,8 +2830,8 @@ no option http-server-close
If this option has been enabled in a "defaults" section, it can be disabled If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it. in a specific instance by prepending the "no" keyword before it.
See also : "option forceclose", "option http-pretend-keepalive" and See also : "option forceclose", "option http-pretend-keepalive",
"option httpclose". "option httpclose" and "1.1. The HTTP transaction model".
option http-use-proxy-header option http-use-proxy-header
@ -2913,15 +2923,13 @@ no option httpclose
yes | yes | yes | yes yes | yes | yes | yes
Arguments : none Arguments : none
As stated in section 1, HAProxy does not yet support the HTTP keep-alive By default, when a client communicates with a server, HAProxy will only
mode. So by default, if a client communicates with a server in this mode, it analyze, log, and process the first request of each connection. If "option
will only analyze, log, and process the first request of each connection. To httpclose" is set, it will check if a "Connection: close" header is already
workaround this limitation, it is possible to specify "option httpclose". It set in each direction, and will add one if missing. Each end should react to
will check if a "Connection: close" header is already set in each direction, this by actively closing the TCP connection after each transfer, thus
and will add one if missing. Each end should react to this by actively resulting in a switch to the HTTP close mode. Any "Connection" header
closing the TCP connection after each transfer, thus resulting in a switch to different from "close" will also be removed.
the HTTP close mode. Any "Connection" header different from "close" will also
be removed.
It seldom happens that some servers incorrectly ignore this header and do not It seldom happens that some servers incorrectly ignore this header and do not
close the connection eventhough they reply "Connection: close". For this close the connection eventhough they reply "Connection: close". For this
@ -2940,7 +2948,8 @@ no option httpclose
If this option has been enabled in a "defaults" section, it can be disabled If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it. in a specific instance by prepending the "no" keyword before it.
See also : "option forceclose" and "option http-server-close" See also : "option forceclose", "option http-server-close" and
"1.1. The HTTP transaction model".
option httplog [ clf ] option httplog [ clf ]