svn commit: r1823750 - /httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en

[el...@apache.org]

Author: elukey
Date: Sat Feb 10 12:16:07 2018
New Revision: 1823750

URL: http://svn.apache.org/viewvc?rev=1823750&view=rev
Log:
documentation rebuild

Modified:
    httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en

Modified: httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en?rev=1823750&r1=1823749&r2=1823750&view=diff
==============================================================================
--- httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en (original)
+++ httpd/httpd/trunk/docs/manual/mod/mod_proxy_fcgi.html.en Sat Feb 10 12:16:07 2018
@@ -92,6 +92,30 @@
     <div class="example"><h3>Single application instance, connection reuse (2.4.11 and later)</h3><pre class="prettyprint lang-config">ProxyPass "/myapp/" "fcgi://localhost:4000/" enablereuse=on</pre>
 </div>
 
+    <div class="note"><h3>Enable connection reuse to a FCGI backend like PHP-FPM</h3>
+    <p>Please keep in mind that PHP-FPM (at the time of writing, February 2018)
+    uses a prefork model, namely each of its worker processes can handle one
+    connection at the time.<br /> 
+    By default mod_proxy (configured with <code>enablereuse=on</code>)
+    allows a connection pool of
+    <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> connections to the
+    backend for each httpd process, so the following use cases should be taken
+    into account:</p>
+    <ul>
+      <li>Under HTTP/1.1 load it will likely cause the creation of up to
+      <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
+      connections to the FCGI backend.</li>
+      <li>Under HTTP/2 load, due to how <code class="module"><a href="../mod/mod_http2.html">mod_http2</a></code> is implemented,
+      there are additional h2 worker threads that may force the creation of other
+      backend connections. The overall count of connections in the pools may raise
+      to more than <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>.</li>
+    </ul>
+    <p>The maximum number of PHP-FPM worker processes needs to be configured wisely,
+    since there is the chance that they will all end up "busy" handling idle
+    persistent connections, without any room for new ones to be established,
+    and the end user experience will be a pile of HTTP request timeouts.</p>
+    </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