I have recently got some basic mod-proxy concepts
and these simple info would have helped me a lot:
- connection pooling == reuse. My brain did not pick
up this simple nomenclature at first read for some
reason, probably because we have parameters called
"*reuse*" and not "*pooling*". I find the term
"reuse" clearer than "pooling", but this is
debatable :)
- the concept of "Worker" needs to be read before
the ProxyPass section (that people probably read
directly after checking a search engine) to fully
understand its power.
- the fact that a worker is related to a single process
(and not shared as a Balancer) is a really important
concept that I tried to highlight when talking
about maxconns (question popped up a lot of times
from users).
Hope that my understanding is correct, feedback is welcome.
git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@
1803171 13f79535-47bb-0310-9956-
ffa450edef68
<p>The two default workers have a fixed configuration
and will be used if no other worker matches the request.
- They do not use HTTP Keep-Alive or connection pooling.
+ They do not use HTTP Keep-Alive or connection reuse.
The TCP connections to the origin server will instead be
opened and closed for each request.</p>
<div class="note"><h3>DNS resolution for origin domains</h3>
<p>DNS resolution happens when the socket to
the origin domain is created for the first time.
- When connection pooling is used, each backend domain is resolved
- only once per child process, and reused for all further connections
+ When connection reuse is enabled, each backend domain is resolved
+ only once per child process, and cached for all further connections
until the child is recycled. This information should to be considered
while planning DNS maintenance tasks involving backend domains.
Please also check <code class="directive"><a href="#proxypass">ProxyPass</a></code>
a local virtual path; <var>url</var> is a partial URL for the
remote server and cannot include a query string.</p>
- <div class="note"><strong>Note: </strong>This directive is not supported within
+ <div class="note">It is strongly suggested to review the concept of a
+ <a href="#workers">Worker</a> before proceeding any further
+ with this section.</div>
+
+ <div class="note">This directive is not supported within
<code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> and
<code class="directive"><a href="../mod/core.html#files"><Files></a></code> containers.</div>
using <code>key=value</code> parameters, described in the tables
below.</p>
+ <div class="warning"><h3>Maximum connections to the backend</h3>
<p>By default, mod_proxy will allow and retain the maximum number of
connections that could be used simultaneously by that web server child
process. Use the <code>max</code> parameter to reduce the number from
- the default. Use the <code>ttl</code> parameter to set an optional
+ the default. The pool of connections is maintained per web server child
+ process, and <code>max</code> and other settings are not coordinated
+ among all child processes, except when only one child process is allowed
+ by configuration or MPM design.</p>
+ </div>
+
+ <p>Use the <code>ttl</code> parameter to set an optional
time to live; connections which have been unused for at least
<code>ttl</code> seconds will be closed. <code>ttl</code> can be used
to avoid using a connection which is subject to closing because of the
backend server's keep-alive timeout.</p>
- <p>The pool of connections is maintained per web server child
- process, and <code>max</code> and other settings are not coordinated
- among all child processes, except when only one child process is allowed
- by configuration or MPM design.</p>
-
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">ProxyPass "/example" "http://backend.example.com" max=20 ttl=120 retry=300</pre>
</div>
- <table class="bordered"><tr><th>BalancerMember parameters</th></tr></table>
+ <table class="bordered"><tr><th>Worker|BalancerMember parameters</th></tr></table>
<table>
<tr><th>Parameter</th>
<th>Default</th>
httpd and
the backend server (regardless of protocol) tends to silently
drop connections or when backends themselves may be under round-
- robin DNS. To disable connection pooling reuse,
+ robin DNS. To disable connection reuse,
set this property value to <code>On</code>.
</td></tr>
<tr><td>enablereuse</td>
<p>The two default workers have a fixed configuration
and will be used if no other worker matches the request.
- They do not use HTTP Keep-Alive or connection pooling.
+ They do not use HTTP Keep-Alive or connection reuse.
The TCP connections to the origin server will instead be
opened and closed for each request.</p>
<note><title>DNS resolution for origin domains</title>
<p>DNS resolution happens when the socket to
the origin domain is created for the first time.
- When connection pooling is used, each backend domain is resolved
- only once per child process, and reused for all further connections
+ When connection reuse is enabled, each backend domain is resolved
+ only once per child process, and cached for all further connections
until the child is recycled. This information should to be considered
while planning DNS maintenance tasks involving backend domains.
Please also check <directive module="mod_proxy">ProxyPass</directive>
a local virtual path; <var>url</var> is a partial URL for the
remote server and cannot include a query string.</p>
- <note><strong>Note: </strong>This directive is not supported within
+ <note>It is strongly suggested to review the concept of a
+ <a href="#workers">Worker</a> before proceeding any further
+ with this section.</note>
+
+ <note>This directive is not supported within
<directive type="section" module="core">Directory</directive> and
<directive type="section" module="core">Files</directive> containers.</note>
using <code>key=value</code> parameters, described in the tables
below.</p>
+ <note type="warning"><title>Maximum connections to the backend</title>
<p>By default, mod_proxy will allow and retain the maximum number of
connections that could be used simultaneously by that web server child
process. Use the <code>max</code> parameter to reduce the number from
- the default. Use the <code>ttl</code> parameter to set an optional
+ the default. The pool of connections is maintained per web server child
+ process, and <code>max</code> and other settings are not coordinated
+ among all child processes, except when only one child process is allowed
+ by configuration or MPM design.</p>
+ </note>
+
+ <p>Use the <code>ttl</code> parameter to set an optional
time to live; connections which have been unused for at least
<code>ttl</code> seconds will be closed. <code>ttl</code> can be used
to avoid using a connection which is subject to closing because of the
backend server's keep-alive timeout.</p>
- <p>The pool of connections is maintained per web server child
- process, and <code>max</code> and other settings are not coordinated
- among all child processes, except when only one child process is allowed
- by configuration or MPM design.</p>
-
<example><title>Example</title>
<highlight language="config">
ProxyPass "/example" "http://backend.example.com" max=20 ttl=120 retry=300
</highlight>
</example>
- <table border="2"><tr><th>BalancerMember parameters</th></tr></table>
+ <table border="2"><tr><th>Worker|BalancerMember parameters</th></tr></table>
<table>
<tr><th>Parameter</th>
<th>Default</th>
httpd and
the backend server (regardless of protocol) tends to silently
drop connections or when backends themselves may be under round-
- robin DNS. To disable connection pooling reuse,
+ robin DNS. To disable connection reuse,
set this property value to <code>On</code>.
</td></tr>
<tr><td>enablereuse</td>
<p> The following example passes the request URI as a filesystem
path for the PHP-FPM daemon to run. The request URL is implicitly added
to the 2nd parameter. The hostname and port following fcgi:// are where
- PHP-FPM is listening. Connection pooling is enabled.</p>
+ PHP-FPM is listening. Connection pooling/reuse is enabled.</p>
<div class="example"><h3>PHP-FPM</h3><pre class="prettyprint lang-config">ProxyPassMatch "^/myapp/.*\.php(/.*)?$" "fcgi://localhost:9000/var/www/" enablereuse=on</pre>
</div>
<p> The following example passes the request URI as a filesystem
path for the PHP-FPM daemon to run. The request URL is implicitly added
to the 2nd parameter. The hostname and port following fcgi:// are where
- PHP-FPM is listening. Connection pooling is enabled.</p>
+ PHP-FPM is listening. Connection pooling/reuse is enabled.</p>
<example><title>PHP-FPM</title>
<highlight language="config">
ProxyPassMatch "^/myapp/.*\.php(/.*)?$" "fcgi://localhost:9000/var/www/" enablereuse=on
<p>Using this flag triggers the use of <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>, without handling of persistent connections. This
means the performance of your proxy will be better if you set it up with <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> or
<code class="directive"><a href="../mod/mod_proxy.html#proxypassmatch">ProxyPassMatch</a></code></p>
-<p>This is because this flag triggers the use of the default worker, which does not handle connection pooling.</p>
+<p>This is because this flag triggers the use of the default worker, which does not handle connection pooling/reuse.</p>
<p>Avoid using this flag and prefer those directives, whenever you can.</p>
</div>
<p>Using this flag triggers the use of <module>mod_proxy</module>, without handling of persistent connections. This
means the performance of your proxy will be better if you set it up with <directive module="mod_proxy">ProxyPass</directive> or
<directive module="mod_proxy">ProxyPassMatch</directive></p>
-<p>This is because this flag triggers the use of the default worker, which does not handle connection pooling.</p>
+<p>This is because this flag triggers the use of the default worker, which does not handle connection pooling/reuse.</p>
<p>Avoid using this flag and prefer those directives, whenever you can.</p>
</note>
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