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diff --git a/docs/manual/mod/mod_http2.html.en b/docs/manual/mod/mod_http2.html.en new file mode 100644 index 0000000..cdccaf2 --- /dev/null +++ b/docs/manual/mod/mod_http2.html.en @@ -0,0 +1,970 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> +<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" /> +<!-- + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + This file is generated from xml source: DO NOT EDIT + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + --> +<title>mod_http2 - Apache HTTP Server Version 2.4</title> +<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> +<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> +<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" /> +<script src="../style/scripts/prettify.min.js" type="text/javascript"> +</script> + +<link href="../images/favicon.ico" rel="shortcut icon" /></head> +<body> +<div id="page-header"> +<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> +<p class="apache">Apache HTTP Server Version 2.4</p> +<img alt="" src="../images/feather.png" /></div> +<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> +<div id="path"> +<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> +<div id="page-content"> +<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> | +<a href="../fr/mod/mod_http2.html" hreflang="fr" rel="alternate" title="Français"> fr </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> +<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.17 and later</td></tr></table> +<h3>Summary</h3> + + <p>This module provides HTTP/2 (<a href="https://tools.ietf.org/html/rfc7540">RFC 7540</a>) + 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> + + <p>You must enable HTTP/2 via <code class="directive"><a href="../mod/core.html#protocols">Protocols</a></code> + in order to use the functionality described in this document. The + HTTP/2 protocol <a href="https://http2.github.io/faq/#does-http2-require-encryption">does not require</a> the use of encryption so two schemes are available: + <code>h2</code> (HTTP/2 over TLS) and <code>h2c</code> (HTTP/2 over TCP).</p> + + <p>Two useful configuration schemes are:</p> + + <div class="note"><h3>HTTP/2 in a VirtualHost context (TLS only)</h3> + <pre class="prettyprint lang-config">Protocols h2 http/1.1</pre> + + <p>Allows HTTP/2 negotiation (h2) via TLS ALPN in a secure + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>. + HTTP/2 preamble checking (Direct mode, see <code class="directive"><a href="#h2direct">H2Direct</a></code>) is disabled by default for <code>h2</code>.</p> + </div> + + <div class="note"><h3>HTTP/2 in a Server context (TLS and cleartext)</h3> + <pre class="prettyprint lang-config">Protocols h2 h2c http/1.1</pre> + + <p>Allows HTTP/2 negotiation (h2) via TLS ALPN for secure + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>. Allows + HTTP/2 cleartext negotiation (h2c) upgrading from an initial HTTP/1.1 + connection or via HTTP/2 preamble checking (Direct mode, see + <code class="directive"><a href="#h2direct">H2Direct</a></code>).</p> + </div> + + <p>Refer to the official <a href="https://http2.github.io/faq">HTTP/2 FAQ</a> + for any doubt about the protocol.</p> + + </div> +<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3> +<ul id="topics"> +<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it works</a></li> +</ul><h3 class="directives">Directives</h3> +<ul id="toc"> +<li><img alt="" src="../images/down.gif" /> <a href="#h2copyfiles">H2CopyFiles</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2direct">H2Direct</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2earlyhints">H2EarlyHints</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="#h2moderntlsonly">H2ModernTLSOnly</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2outputbuffering">H2OutputBuffering</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2padding">H2Padding</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2push">H2Push</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2pushdiarysize">H2PushDiarySize</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2pushpriority">H2PushPriority</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2pushresource">H2PushResource</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2serializeheaders">H2SerializeHeaders</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2streammaxmemsize">H2StreamMaxMemSize</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2tlscooldownsecs">H2TLSCoolDownSecs</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2tlswarmupsize">H2TLSWarmUpSize</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2upgrade">H2Upgrade</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#h2windowsize">H2WindowSize</a></li> +</ul> +<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_http2">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_http2">Report a bug</a></li></ul><h3>See also</h3> +<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="section"> +<h2><a name="how-it-works" id="how-it-works">How it works</a></h2> + + <h3><a name="dimensioning" id="dimensioning">HTTP/2 Dimensioning</a></h3> + <p> + Enabling HTTP/2 on your Apache Server has impact on the resource + consumption and if you have a busy site, you may need to consider + carefully the implications. + </p> + <p> + The first noticeable thing after enabling HTTP/2 is that your server + processes will start additional threads. The reason for this is that + HTTP/2 gives all requests that it receives to its own <em>Worker</em> + threads for processing, collects the results and streams them out + to the client. + </p> + <p> + In the current implementation, these workers use a separate thread + pool from the MPM workers that you might be familiar with. This is + just how things are right now and not intended to be like this forever. + (It might be forever for the 2.4.x release line, though.) So, HTTP/2 + workers, or shorter H2Workers, will not show up in <code class="module"><a href="../mod/mod_status.html">mod_status</a></code>. They + are also not counted against directives such as <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>. However + they take <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> + as default if you have not configured something + else via <code class="directive"><a href="#h2minworkers">H2MinWorkers</a></code> and + <code class="directive"><a href="#h2maxworkers">H2MaxWorkers</a></code>. + </p> + <p> + Another thing to watch out for is is memory consumption. Since HTTP/2 + keeps more state on the server to manage all the open request, priorities + for and dependencies between them, it will always need more memory + than HTTP/1.1 processing. There are three directives which steer the + memory footprint of a HTTP/2 connection: + <code class="directive"><a href="#h2maxsessionstreams">H2MaxSessionStreams</a></code>, + <code class="directive"><a href="#h2windowsize">H2WindowSize</a></code> and + <code class="directive"><a href="#h2streammaxmemsize">H2StreamMaxMemSize</a></code>. + </p> + <p> + <code class="directive"><a href="#h2maxsessionstreams">H2MaxSessionStreams</a></code> limits the + number of parallel requests that a client can make on a HTTP/2 connection. + It depends on your site how many you should allow. The default is 100 which + is plenty and unless you run into memory problems, I would keep it this + way. Most requests that browsers send are GETs without a body, so they + use up only a little bit of memory until the actual processing starts. + </p> + <p> + <code class="directive"><a href="#h2windowsize">H2WindowSize</a></code> controls how much + the client is allowed to send as body of a request, before it waits + for the server to encourage more. Or, the other way around, it is the + amount of request body data the server needs to be able to buffer. This + is per request. + </p> + <p> + And last, but not least, <code class="directive"><a href="#h2streammaxmemsize">H2StreamMaxMemSize</a></code> + controls how much response data shall be buffered. The request sits in + a H2Worker thread and is producing data, the HTTP/2 connection tries + to send this to the client. If the client does not read fast enough, + the connection will buffer this amount of data and then suspend the + H2Worker. + </p> + + + <h3><a name="misdirected" id="misdirected">Multiple Hosts and Misdirected Requests</a></h3> + <p> + Many sites use the same TLS certificate for multiple virtual hosts. The + certificate either has a wildcard name, such as '*.example.org' or carries + several alternate names. Browsers using HTTP/2 will recognize that and reuse + an already opened connection for such hosts. + </p> + <p> + While this is great for performance, it comes at a price: such vhosts + need more care in their configuration. The problem is that you will have + multiple requests for multiple hosts on the same TLS connection. And that + makes renegotiation impossible, in face the HTTP/2 standard forbids it. + </p> + <p> + So, if you have several virtual hosts using the same certificate and + want to use HTTP/2 for them, you need to make sure that all vhosts have + exactly the same SSL configuration. You need the same protocol, + ciphers and settings for client verification. + </p> + <p> + If you mix things, Apache httpd will detect it and return a special + response code, 421 Misdirected Request, to the client. + </p> + + + <h3><a name="envvars" id="envvars">Environment Variables</a></h3> + <p> + This module can be configured to provide HTTP/2 related information + as additional environment variables to the SSI and CGI namespace, as well + as in custom log configurations (see <code>%{VAR_NAME}e</code>). + </p> + + <table class="bordered"> + + <tr> + <th><a name="table3">Variable Name:</a></th> + <th>Value Type:</th> + <th>Description:</th> + </tr> + <tr><td><code>HTTP2</code></td><td>flag</td><td>HTTP/2 is being used.</td></tr> + <tr><td><code>H2PUSH</code></td><td>flag</td><td>HTTP/2 Server Push is enabled for this connection and also supported by the client.</td></tr> + <tr><td><code>H2_PUSH</code></td><td>flag</td><td>alternate name for <code>H2PUSH</code></td></tr> + <tr><td><code>H2_PUSHED</code></td><td>string</td><td>empty or <code>PUSHED</code> for a request being pushed by the server.</td></tr> + <tr><td><code>H2_PUSHED_ON</code></td><td>number</td><td>HTTP/2 stream number that triggered the push of this request.</td></tr> + <tr><td><code>H2_STREAM_ID</code></td><td>number</td><td>HTTP/2 stream number of this request.</td></tr> + <tr><td><code>H2_STREAM_TAG</code></td><td>string</td><td>HTTP/2 process unique stream identifier, consisting of connection id and stream id separated by <code>-</code>.</td></tr> + </table> + + + </div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="H2CopyFiles" id="H2CopyFiles">H2CopyFiles</a> <a name="h2copyfiles" id="h2copyfiles">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Determine file handling in responses</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2CopyFiles on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2CopyFiles off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.24 and later.</td></tr> +</table> + <p> + This directive influences how file content is handled in + responses. When <code>off</code>, which is the default, file handles + are passed from the requestion processing down to the main + connection, using the usual Apache setaside handling for + managing the lifetime of the file. + </p> + <p> + When set to <code>on</code>, file content is copied while the + request is still being processed and the buffered data is passed + on to the main connection. This is better if a third party + module is injecting files with different lifetimes into the response. + </p> + <p> + An example for such a module is <code>mod_wsgi</code> that may place + Python file handles into the response. Those files get close down when + Python thinks processing has finished. That may be well before + <code class="module"><a href="../mod/mod_http2.html">mod_http2</a></code> is done with them. + </p> + +</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 h2c, off for h2 protocol</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. + </p> + <p> + 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 is defined in RFC 7540 for the cleartext (h2c) case. Its + use on TLS connections not mandated by the standard. + </p> + <p> + When a server/vhost does not have h2 or h2c enabled via + <code class="directive"><a href="../mod/core.html#protocols">Protocols</a></code>, + the connection is never inspected for a HTTP/2 preamble. + <code class="directive">H2Direct</code> + does not matter then. This is important for connections that + use protocols where an initial read might hang indefinitely, such + as NNTP. + </p> + <p> + For clients that have out-of-band knowledge about a server + supporting h2c, direct HTTP/2 saves the client from having to + perform an HTTP/1.1 upgrade, resulting in better performance + and avoiding the Upgrade restrictions on request bodies. + </p> + <p> + This makes direct h2c attractive for server to server communication + as well, when the connection can be trusted or is secured by other means. + </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="H2EarlyHints" id="H2EarlyHints">H2EarlyHints</a> <a name="h2earlyhints" id="h2earlyhints">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Determine sending of 103 status codes</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2EarlyHints on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2EarlyHints 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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.24 and later.</td></tr> +</table> + <p> + This setting controls if HTTP status 103 interim responses are + forwarded to the client or not. By default, this is currently + not the case since a range of clients still have trouble with + unexpected interim responses. + </p> + <p> + When set to <code>on</code>, PUSH resources announced with + <code class="directive"><a href="#h2pushresource">H2PushResource</a></code> will + trigger an interim 103 response + before the final response. The 103 response will carry <code>Link</code> + headers that advise the <code>preload</code> of such resources. + </p> + +</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 class="directive"><a href="#h2minworkers">H2MinWorkers</a></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 class="module"><a href="../mod/mod_http2.html">mod_http2</a></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 class="module"><a href="../mod/mod_http2.html">mod_http2</a></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="H2ModernTLSOnly" id="H2ModernTLSOnly">H2ModernTLSOnly</a> <a name="h2moderntlsonly" id="h2moderntlsonly">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Require HTTP/2 connections to be "modern TLS" only</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2ModernTLSOnly on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2ModernTLSOnly on</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.18 and later.</td></tr> +</table> + <p> + This directive toggles the security checks on HTTP/2 connections + in TLS mode (https:). This can be used server wide or for specific + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>s. + </p> + <p> + The security checks require that the TSL protocol is at least + TLSv1.2 and that none of the ciphers listed in RFC 7540, Appendix A + is used. These checks will be extended once new security requirements + come into place. + </p> + <p> + The name stems from the + <a href="https://wiki.mozilla.org/Security/Server_Side_TLS">Security/Server Side TLS</a> + definitions at mozilla where "modern compatibility" is defined. Mozilla Firefox and + other browsers require modern compatibility for HTTP/2 connections. As everything + in OpSec, this is a moving target and can be expected to evolve in the future. + </p> + <p> + One purpose of having these checks in <code class="module"><a href="../mod/mod_http2.html">mod_http2</a></code> is to enforce this + security level for all connections, not only those from browsers. The other + purpose is to prevent the negotiation of HTTP/2 as a protocol should + the requirements not be met. + </p> + <p> + Ultimately, the security of the TLS connection is determined by the + server configuration directives for <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code>. + </p> + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2ModernTLSOnly off</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="H2OutputBuffering" id="H2OutputBuffering">H2OutputBuffering</a> <a name="h2outputbuffering" id="h2outputbuffering">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Determine buffering behaviour of output</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2OutputBuffering on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2OutputBuffering on</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.48 and later.</td></tr> +</table> + <p> + The directive <code class="directive">H2OutputBuffering</code> controls the buffering of stream output. + The default is on, which is the behaviour of previous versions. When off, all + bytes are made available immediately to the main connection for sending them + out to the client. This fixes interop issues with certain flavours of gRPC. + </p> + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="H2Padding" id="H2Padding">H2Padding</a> <a name="h2padding" id="h2padding">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Determine the range of padding bytes added to payload frames</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2Padding <em>numbits</em></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2Padding 0</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.39 and later.</td></tr> +</table> + <p> + With the default 0, no padding bytes are added to any payload + frames, e.g. HEADERS, DATA and PUSH_PROMISE. This is the behaviour + of previous versions. It means that under certain conditions, an + observer of network traffic can see the length of those frames + in the TLS stream. + </p> + <p> + When configuring numbits of 1-8, a random number in range + [0, 2^numbits[ are added to each frame. The random value is chosen + independently for each frame that the module sends back to the client. + </p> + <p> + While more padding bytes give better message length obfuscation, they + are also additional traffic. The optimal number therefore depends on + the kind of web traffic the server carries. + </p> + <p> + The default of 0, e.g. no padding, was chosen for maximum backward + compatibility. There might be deployments where padding bytes are + unwanted or do harm. The most likely cause would be a client that + has a faults implementation. + </p> + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="H2Push" id="H2Push">H2Push</a> <a name="h2push" id="h2push">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>H2 Server Push Switch</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2Push on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2Push on</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.18 and later.</td></tr> +</table> + <p> + This directive toggles the usage of the HTTP/2 server push + protocol feature. + </p> + <p> + The HTTP/2 protocol allows the server to push other resources to + a client when it asked for a particular one. This is helpful + if those resources are connected in some way and the client can + be expected to ask for it anyway. The pushing then saves the + time it takes the client to ask for the resources itself. On the + other hand, pushing resources the client never needs or already + has is a waste of bandwidth. + </p> + <p> + Server pushes are detected by inspecting the <code>Link</code> headers of + responses (see https://tools.ietf.org/html/rfc5988 for the + specification). When a link thus specified has the <code>rel=preload</code> + attribute, it is treated as a resource to be pushed. + </p> + <p> + Link headers in responses are either set by the application or + can be configured via <code class="directive"><a href="#h2pushresource">H2PushResource</a></code> or + using <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> as: + </p> + <div class="example"><h3>mod_headers example</h3><pre class="prettyprint lang-config"><Location /index.html> + Header add Link "</css/site.css>;rel=preload" + Header add Link "</images/logo.jpg>;rel=preload" +</Location></pre> +</div> + <p> + As the example shows, there can be several link headers added + to a response, resulting in several pushes being triggered. There + are no checks in the module to avoid pushing the same resource + twice or more to one client. Use with care. + </p> + <p> + HTTP/2 server pushes are enabled by default. On a server or virtual host, + you may enable/disable this feature for any connection to the host. In addition, + you may disable PUSH for a set of resources in a Directory/Location. This controls + which resources may cause a PUSH, not which resources may be sent via PUSH. + </p> + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2Push off</pre> +</div> + <p> + Last but not least, pushes happen only when the client signals + its willingness to accept those. Most browsers do, some, like Safari 9, + do not. Also, pushes also only happen for resources from the same + <em>authority</em> as the original response is for. + </p> + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="H2PushDiarySize" id="H2PushDiarySize">H2PushDiarySize</a> <a name="h2pushdiarysize" id="h2pushdiarysize">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>H2 Server Push Diary Size</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2PushDiarySize <em>n</em></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2PushDiarySize 256</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.19 and later.</td></tr> +</table> + <p> + This directive toggles the maximum number of HTTP/2 server pushes + that are remembered per HTTP/2 connection. This can be used inside the + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> + section to influence the number for all connections to that virtual host. + </p> + <p> + The push diary records a digest of pushed + resources (their URL) to avoid duplicate pushes on the same connection. + These value are not persisted, so clients opening a new connection + will experience known pushes again. + </p> + <p> + If the maximum size is reached, newer entries replace the oldest + ones. A diary entry uses 8 bytes, letting a + default diary with 256 entries consume around 2 KB of memory. + </p> + <p> + A size of 0 will effectively disable the push diary. + </p> + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="H2PushPriority" id="H2PushPriority">H2PushPriority</a> <a name="h2pushpriority" id="h2pushpriority">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>H2 Server Push Priority</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2PushPriority <em>mime-type</em> [after|before|interleaved] [<em>weight</em>]</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2PushPriority * After 16</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.18 and later. For having an + effect, a nghttp2 library version 1.5.0 or newer is necessary.</td></tr> +</table> + <p> + This directive defines the priority handling of pushed responses + based on the content-type of the response. This is usually defined + per server config, but may also appear in a virtual host. + </p> + <p> + HTTP/2 server pushes are always related to a client request. Each + such request/response pairs, or <em>streams</em> have a dependency + and a weight, together defining the <em>priority</em> of a stream. + </p> + <p> + When a stream <em>depends</em> on another, say X depends on Y, + then Y gets all bandwidth before X gets any. Note that this + does not mean that Y will block X. If Y has no data to send, + all bandwidth allocated to Y can be used by X. + </p> + <p> + When a stream has more than one dependent, say X1 and X2 both + depend on Y, the <em>weight</em> determines the bandwidth + allocation. If X1 and X2 have the same weight, they both get + half of the available bandwidth. If the weight of X1 is twice + as large as that for X2, X1 gets twice the bandwidth of X2. + </p> + <p> + Ultimately, every stream depends on the <em>root</em> stream which + gets all the bandwidth available, but never sends anything. So all + its bandwidth is distributed by weight among its children. Which + either have data to send or distribute the bandwidth to their + own children. And so on. If none of the children have data + to send, that bandwidth get distributed somewhere else according + to the same rules. + </p> + <p> + The purpose of this priority system is to always make use of + available bandwidth while allowing precedence and weight + to be given to specific streams. Since, normally, all streams + are initiated by the client, it is also the one that sets + these priorities. + </p> + <p> + Only when such a stream results in a PUSH, gets the server to + decide what the <em>initial</em> priority of such a pushed + stream is. In the examples below, X is the client stream. It + depends on Y and the server decides to PUSH streams P1 and P2 + onto X. + </p> + <p> + The default priority rule is: + </p> + <div class="example"><h3>Default Priority Rule</h3><pre class="prettyprint lang-config">H2PushPriority * After 16</pre> +</div> + <p> + which reads as 'Send a pushed stream of any content-type + depending on the client stream with weight 16'. And so P1 + and P2 will be send after X and, as they have equal weight, + share bandwidth equally among themselves. + </p> + <div class="example"><h3>Interleaved Priority Rule</h3><pre class="prettyprint lang-config">H2PushPriority text/css Interleaved 256</pre> +</div> + <p> + which reads as 'Send any CSS resource on the same dependency and + weight as the client stream'. If P1 has content-type 'text/css', + it will depend on Y (as does X) and its effective weight will be + calculated as <code>P1ew = Xw * (P1w / 256)</code>. With P1w being + 256, this will make the effective weight the same as the weight + of X. If both X and P1 have data to send, bandwidth will be allocated + to both equally. + </p> + <p> + With Pw specified as 512, a pushed, interleaved stream would + get double the weight of X. With 128 only half as much. Note that + effective weights are always capped at 256. + </p> + <div class="example"><h3>Before Priority Rule</h3><pre class="prettyprint lang-config">H2PushPriority application/json Before</pre> +</div> + <p> + This says that any pushed stream of content type 'application/json' + should be send out <em>before</em> X. This makes P1 dependent + on Y and X dependent on P1. So, X will be stalled as long as + P1 has data to send. The effective weight is inherited from the + client stream. Specifying a weight is not allowed. + </p> + <p> + Be aware that the effect of priority specifications is limited + by the available server resources. If a server does not have + workers available for pushed streams, the data for the stream + may only ever arrive when other streams have been finished. + </p> + <p> + Last, but not least, there are some specifics of the syntax + to be used in this directive: + </p> + <ol> + <li>'*' is the only special content-type that matches all others. + 'image/*' will not work.</li> + <li>The default dependency is 'After'. </li> + <li>There are also default weights: for 'After' it is 16, 'interleaved' is 256. + </li> + </ol> + <div class="example"><h3>Shorter Priority Rules</h3><pre class="prettyprint lang-config">H2PushPriority application/json 32 # an After rule +H2PushPriority image/jpeg before # weight inherited +H2PushPriority text/css interleaved # weight 256 default</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="H2PushResource" id="H2PushResource">H2PushResource</a> <a name="h2pushresource" id="h2pushresource">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Declares resources for early pushing to the client</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2PushResource [add] <em>path</em> [critical]</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.24 and later.</td></tr> +</table> + <p> + When added to a directory/location HTTP/2 PUSHes will be attempted + for all paths added via this directive. This directive can be used + several times for the same location. + </p> + <p> + This directive pushes resources much earlier than adding + <code>Link</code> headers via <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code>. + <code class="module"><a href="../mod/mod_http2.html">mod_http2</a></code> announces these resources in a + <code>103 Early Hints</code> interim response to the client. + That means that clients not supporting PUSH will still get + early preload hints. + </p> + <p> + In contrast to setting <code>Link</code> response headers + via <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code>, this directive will only + take effect on HTTP/2 connections. + </p> + <p> + By adding <code>critical</code> to such a resource, the server + will give processing it more preference and send its data, once + available, before the data from the main request. + </p> + +</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="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="H2TLSCoolDownSecs" id="H2TLSCoolDownSecs">H2TLSCoolDownSecs</a> <a name="h2tlscooldownsecs" id="h2tlscooldownsecs">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure the number of seconds of idle time on TLS before shrinking writes</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2TLSCoolDownSecs <em>seconds</em></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2TLSCoolDownSecs 1</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.18 and later.</td></tr> +</table> + <p> + This directive sets the number of seconds of idle time on a TLS + connection before the TLS write size falls back to small (~1300 bytes) + length. + This can be used server wide or for specific + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>s. + </p> + <p> + See <code class="directive"><a href="#h2tlswarmupsize">H2TLSWarmUpSize</a></code> for a + description of TLS warmup. <code class="directive">H2TLSCoolDownSecs</code> reflects the fact + that connections may deteriorate over time (and TCP flow adjusts) + for idle connections as well. It is beneficial to overall performance + to fall back to the pre-warmup phase after a number of seconds that + no data has been sent. + </p> + <p> + In deployments where connections can be considered reliable, this + timer can be disabled by setting it to 0. + </p> + <p> + The following example sets the seconds to zero, effectively disabling + any cool down. Warmed up TLS connections stay on maximum record + size. + </p> + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2TLSCoolDownSecs 0</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="H2TLSWarmUpSize" id="H2TLSWarmUpSize">H2TLSWarmUpSize</a> <a name="h2tlswarmupsize" id="h2tlswarmupsize">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure the number of bytes on TLS connection before doing max writes</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2TLSWarmUpSize <em>amount</em></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2TLSWarmUpSize 1048576</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> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.4.18 and later.</td></tr> +</table> + <p> + This directive sets the number of bytes to be sent in small + TLS records (~1300 bytes) until doing maximum sized writes (16k) + on https: HTTP/2 connections. + This can be used server wide or for specific + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>s. + </p> + <p> + Measurements by <a href="https://www.igvita.com">google performance + labs</a> show that best performance on TLS connections is reached, + if initial record sizes stay below the MTU level, to allow a + complete record to fit into an IP packet. + </p> + <p> + While TCP adjust its flow-control and window sizes, longer TLS + records can get stuck in queues or get lost and need retransmission. + This is of course true for all packets. TLS however needs the + whole record in order to decrypt it. Any missing bytes at the end + will stall usage of the received ones. + </p> + <p> + After a sufficient number of bytes have been send successfully, + the TCP state of the connection is stable and maximum TLS record + sizes (16 KB) can be used for optimal performance. + </p> + <p> + In deployments where servers are reached locally or over reliable + connections only, the value might be decreased with 0 disabling + any warmup phase altogether. + </p> + <p> + The following example sets the size to zero, effectively disabling + any warmup phase. + </p> + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2TLSWarmUpSize 0</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="H2Upgrade" id="H2Upgrade">H2Upgrade</a> <a name="h2upgrade" id="h2upgrade">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>H2 Upgrade Protocol Switch</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2Upgrade on|off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2Upgrade on for h2c, off for h2 protocol</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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/1.1 Upgrade method + for switching to HTTP/2. This + should be used inside a + <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> + section to enable Upgrades to HTTP/2 for that virtual host. + </p> + <p> + This method of switching protocols is defined in HTTP/1.1 and + uses the "Upgrade" header (thus the name) to announce willingness + to use another protocol. This may happen on any request of a + HTTP/1.1 connection. + </p> + <p> + This method of protocol switching is enabled by default on cleartext + (potential h2c) connections and disabled on TLS (potential h2), + as mandated by RFC 7540. + </p> + <p> + Please be aware that Upgrades are only accepted for requests + that carry no body. POSTs and PUTs with content will never + trigger an upgrade to HTTP/2. + See <code class="directive"><a href="#h2direct">H2Direct</a></code> for an + alternative to Upgrade. + </p> + <p> + This mode only has an effect when h2 or h2c is enabled via + the <code class="directive"><a href="../mod/core.html#protocols">Protocols</a></code>. + </p> + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2Upgrade 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="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 65535</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> | +<a href="../fr/mod/mod_http2.html" hreflang="fr" rel="alternate" title="Français"> fr </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 by our moderators if they are either implemented or considered invalid/off-topic. 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