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<?xml version="1.0" encoding="ISO-8859-1"?>
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<title>mod_http2 - Apache HTTP Server Version 2.4</title>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.4</a> > <a href="./">Modules</a></div>
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<div id="preamble"><h1>Apache Module mod_http2</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_http2.html" title="English"> en </a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Support for the HTTP/2 transport layer</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>http2_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_http2.c</td></tr></table>
<h3>Summary</h3>
<p>This module provides HTTP/2 (RFC 7540) support for the Apache
HTTP Server.</p>
<p>This module relies on <a href="http://nghttp2.org/">libnghttp2</a>
to provide the core http/2 engine.</p>
<div class="warning"><h3>Warning</h3>
<p>This module is experimental. Its behaviors, directives, and
defaults are subject to more change from release to
release relative to other standard modules. Users are encouraged to
consult the "CHANGES" file for potential updates.</p>
</div>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#h2direct">H2Direct</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2maxsessionstreams">H2MaxSessionStreams</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2maxworkeridleseconds">H2MaxWorkerIdleSeconds</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2maxworkers">H2MaxWorkers</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2minworkers">H2MinWorkers</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2serializeheaders">H2SerializeHeaders</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2sessionextrafiles">H2SessionExtraFiles</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2streammaxmemsize">H2StreamMaxMemSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#h2windowsize">H2WindowSize</a></li>
</ul>
<ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2Direct" id="H2Direct">H2Direct</a> <a name="h2direct" id="h2direct">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>H2 Direct Protocol Switch</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2Direct on|off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2Direct on (for non TLS)</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive toggles the usage of the HTTP/2 Direct Mode. This
should be used inside a
<code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>
section to enable direct HTTP/2 communication for that virtual host.
Direct communication means that if the first bytes received by the
server on a connection match the HTTP/2 preamble, the HTTP/2
protocol is switched to immediately without further negotiation.
This mode falls outside the RFC 7540 but has become widely implemented
as it is very convenient for development and testing.
By default the direct HTTP/2 mode is enabled.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2Direct on</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2MaxSessionStreams" id="H2MaxSessionStreams">H2MaxSessionStreams</a> <a name="h2maxsessionstreams" id="h2maxsessionstreams">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of active streams per HTTP/2 session.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxSessionStreams <em>n</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2MaxSessionStreams 100</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the maximum number of active streams per HTTP/2 session (e.g. connection)
that the server allows. A stream is active if it is not <code>idle</code> or
<code>closed</code> according to RFC 7540.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2MaxSessionStreams 20</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2MaxWorkerIdleSeconds" id="H2MaxWorkerIdleSeconds">H2MaxWorkerIdleSeconds</a> <a name="h2maxworkeridleseconds" id="h2maxworkeridleseconds">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of seconds h2 workers remain idle until shut down.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxWorkerIdleSeconds <em>n</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2MaxWorkerIdleSeconds 600</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the maximum number of seconds a h2 worker may
idle until it shuts itself down. This only happens while the number of
h2 workers exceeds <code>H2MinWorkers</code>.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2MaxWorkerIdleSeconds 20</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2MaxWorkers" id="H2MaxWorkers">H2MaxWorkers</a> <a name="h2maxworkers" id="h2maxworkers">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of worker threads to use per child process.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxWorkers <em>n</em></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the maximum number of worker threads to spawn
per child process for HTTP/2 processing. If this directive is not used,
<code>mod_http2</code> will chose a value suitable for the <code>mpm</code>
module loaded.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2MaxWorkers 20</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2MinWorkers" id="H2MinWorkers">H2MinWorkers</a> <a name="h2minworkers" id="h2minworkers">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimal number of worker threads to use per child process.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MinWorkers <em>n</em></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the minimum number of worker threads to spawn
per child process for HTTP/2 processing. If this directive is not used,
<code>mod_http2</code> will chose a value suitable for the <code>mpm</code>
module loaded.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2MinWorkers 10</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2SerializeHeaders" id="H2SerializeHeaders">H2SerializeHeaders</a> <a name="h2serializeheaders" id="h2serializeheaders">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Serialize Request/Response Processing Switch</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2SerializeHeaders on|off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2SerializeHeaders off</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive toggles if HTTP/2 requests shall be serialized in
HTTP/1.1 format for processing by <code>httpd</code> core or if
received binary data shall be passed into the <code>request_rec</code>s
directly.
</p>
<p>
Serialization will lower performance, but gives more backward
compatibility in case custom filters/hooks need it.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2SerializeHeaders on</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2SessionExtraFiles" id="H2SessionExtraFiles">H2SessionExtraFiles</a> <a name="h2sessionextrafiles" id="h2sessionextrafiles">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of Extra File Handles</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2SessionExtraFiles <em>n</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2SessionExtraFiles 5</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets maximum number of <em>extra</em> file handles
a HTTP/2 session is allowed to use. A file handle is counted as
<em>extra</em> when it is transfered from a h2 worker thread to
the main HTTP/2 connection handling. This commonly happens when
serving static files.
</p><p>
Depending on the processing model configured on the server, the
number of connections times number of active streams may exceed
the number of file handles for the process. On the other hand,
converting every file into memory bytes early results in too
many buffer writes. This option helps to mitigate that.
</p><p>
The number of file handles used by a server process is then in
the order of:
</p>
<pre>(h2_connections * extra_files) + (h2_max_worker)</pre>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2SessionExtraFiles 10</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2StreamMaxMemSize" id="H2StreamMaxMemSize">H2StreamMaxMemSize</a> <a name="h2streammaxmemsize" id="h2streammaxmemsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of output data buffered per stream.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2StreamMaxMemSize <em>bytes</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2StreamMaxMemSize 65536</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the maximum number of outgoing data bytes buffered in memory
for an active streams. This memory is not allocated per stream as such. Allocations
are counted against this limit when they are about to be done. Stream processing
freezes when the limit has been reached and will only continue when buffered data
has been sent out to the client.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2StreamMaxMemSize 128000</pre>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="H2WindowSize" id="H2WindowSize">H2WindowSize</a> <a name="h2windowsize" id="h2windowsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Size of Stream Window for upstream data.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2WindowSize <em>bytes</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2WindowSize 65536</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_http2</td></tr>
</table>
<p>
This directive sets the size of the window that is used for flow control
from client to server and limits the amount of data the server has to buffer.
The client will stop sending on a stream once the limit has been reached until
the server announces more available space (as it has processed some of the data).
</p><p>
This limit affects only request bodies, not its meta data such as headers. Also,
it has no effect on response bodies as the window size for those are managed
by the clients.
</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2WindowSize 128000</pre>
</div>
</div>
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_http2.html" title="English"> en </a></p>
</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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