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| <title>mod_http2 - Apache HTTP Server Version 2.5</title> | |
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| <p class="apache">Apache HTTP Server Version 2.5</p> | |
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| <a href="https://www.apache.org/">Apache</a> > <a href="https://httpd.apache.org/">HTTP Server</a> > <a href="https://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Modules</a></div> | |
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| <div id="preamble"><h1>Apache Module mod_http2</h1> | |
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| <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://www.rfc-editor.org/rfc/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"><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="#h2earlyhint">H2EarlyHint</a></li> | |
| <li><img alt="" src="../images/down.gif"> <a href="#h2earlyhints">H2EarlyHints</a></li> | |
| <li><img alt="" src="../images/down.gif"> <a href="#h2maxdataframelen">H2MaxDataFrameLen</a></li> | |
| <li><img alt="" src="../images/down.gif"> <a href="#h2maxheaderblocklen">H2MaxHeaderBlockLen</a></li> | |
| <li><img alt="" src="../images/down.gif"> <a href="#h2maxsessionstreams">H2MaxSessionStreams</a></li> | |
| <li><img alt="" src="../images/down.gif"> <a href="#h2maxstreamerrors">H2MaxStreamErrors</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="#h2proxyrequests">H2ProxyRequests</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="#h2streamtimeout">H2StreamTimeout</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="#h2websockets">H2WebSockets</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></div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="section"> | |
| <h2 id="how-it-works">How it works <a title="Permanent link" href="#how-it-works" class="permalink">¶</a></h2> | |
| <h3 id="dimensioning">HTTP/2 Dimensioning</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 id="misdirected">Multiple Hosts and Misdirected Requests</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 id="envvars">Environment Variables</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 id="h2copyfiles"><span id="H2CopyFiles">H2CopyFiles</span> Directive <a title="Permanent link" href="#h2copyfiles" class="permalink">¶</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#Override">Override:</a></th><td>FileInfo</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 request 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 id="h2direct"><span id="H2Direct">H2Direct</span> Directive <a title="Permanent link" href="#h2direct" class="permalink">¶</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 id="h2earlyhint"><span id="H2EarlyHint">H2EarlyHint</span> Directive <a title="Permanent link" href="#h2earlyhint" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add a response header to be picked up in 103 Early Hints</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2EarlyHint <var>name</var> <var>value</var></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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| <code class="directive">H2EarlyHint</code> allows adding a response | |
| header before the real request processing is started. Such headers | |
| are picked up for "103 Early Hints" intermediate responses. The main | |
| purpose is to send "preload" information to client browsers. | |
| </p><p> | |
| <var>name</var> and <var>value</var> must be valid HTTP header fields | |
| or will lead to failed responses. <code class="directive">H2EarlyHints</code> | |
| must still be enabled to allow 103 intermediate responses to be sent. | |
| This directive can be repeated several times and header fields of the | |
| same names add. | |
| </p> | |
| <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">H2EarlyHint Link "</my.css>;rel=preload;as=style"</pre> | |
| </div> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2earlyhints"><span id="H2EarlyHints">H2EarlyHints</span> Directive <a title="Permanent link" href="#h2earlyhints" class="permalink">¶</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 id="h2maxdataframelen"><span id="H2MaxDataFrameLen">H2MaxDataFrameLen</span> Directive <a title="Permanent link" href="#h2maxdataframelen" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum bytes inside a single HTTP/2 DATA frame</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxDataFrameLen <var>n</var></code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2MaxDataFrameLen 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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| <code class="directive">H2MaxDataFrameLen</code> limits the maximum | |
| amount of response body bytes placed into a single HTTP/2 DATA | |
| frame. Setting this to 0 places no limit (but the max size | |
| allowed by the protocol is observed). | |
| </p><p> | |
| The module, by default, tries to use the maximum size possible, | |
| which is somewhat around 16KB. This sets the maximum. When less | |
| response data is available, smaller frames will be sent. | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2maxheaderblocklen"><span id="H2MaxHeaderBlockLen">H2MaxHeaderBlockLen</span> Directive <a title="Permanent link" href="#h2maxheaderblocklen" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum size of response headers</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxHeaderBlockLen <var>n</var></code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2MaxHeaderBlockLen 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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| <code class="directive">H2MaxHeaderBlockLen</code> sets the limit | |
| on the overall size of response headers. A setting of 0 | |
| will leave this at the default of 64 KB in nghttp2. | |
| </p> | |
| <p> | |
| Responses with headers larger than this (adding all headers) | |
| will not be processed and result in a reset of the stream. | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2maxsessionstreams"><span id="H2MaxSessionStreams">H2MaxSessionStreams</span> Directive <a title="Permanent link" href="#h2maxsessionstreams" class="permalink">¶</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 <var>n</var></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 id="h2maxstreamerrors"><span id="H2MaxStreamErrors">H2MaxStreamErrors</span> Directive <a title="Permanent link" href="#h2maxstreamerrors" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of client caused errors to tolerate</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2MaxStreamErrors <var>n</var></code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2MaxStreamErrors 8</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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| <code class="directive">H2MaxStreamErrors</code> sets the maximum amount | |
| of tolerated HTTP/2 stream errors caused by the client. | |
| When exceeding this limit, the connection will be closed. | |
| Stream errors are protocol violations on an individual HTTP/2 | |
| stream that do not necessitate a connection close by the | |
| protocol specification, but can be a sign of malicious | |
| activity by a client. | |
| </p> | |
| <p> | |
| Set to 0 to tolerate faulty clients. | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2maxworkeridleseconds"><span id="H2MaxWorkerIdleSeconds">H2MaxWorkerIdleSeconds</span> Directive <a title="Permanent link" href="#h2maxworkeridleseconds" class="permalink">¶</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 <var>n</var></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 id="h2maxworkers"><span id="H2MaxWorkers">H2MaxWorkers</span> Directive <a title="Permanent link" href="#h2maxworkers" class="permalink">¶</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 <var>n</var></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 id="h2minworkers"><span id="H2MinWorkers">H2MinWorkers</span> Directive <a title="Permanent link" href="#h2minworkers" class="permalink">¶</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 <var>n</var></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 id="h2moderntlsonly"><span id="H2ModernTLSOnly">H2ModernTLSOnly</span> Directive <a title="Permanent link" href="#h2moderntlsonly" class="permalink">¶</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 TLS 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 id="h2outputbuffering"><span id="H2OutputBuffering">H2OutputBuffering</span> Directive <a title="Permanent link" href="#h2outputbuffering" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Determine buffering behavior 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 behavior 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 flavors 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 id="h2padding"><span id="H2Padding">H2Padding</span> Directive <a title="Permanent link" href="#h2padding" class="permalink">¶</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 <var>numbits</var></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 behavior | |
| 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 id="h2proxyrequests"><span id="H2ProxyRequests">H2ProxyRequests</span> Directive <a title="Permanent link" href="#h2proxyrequests" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>En-/Disable forward proxy requests via HTTP/2</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2ProxyRequests on|off</code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2ProxyRequests 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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| Use <code class="directive">H2ProxyRequests</code> to enable or disable | |
| handling of HTTP/2 requests in a forward proxy configuration. | |
| </p><p> | |
| Similar to <code class="directive"><a href="../mod/proxy.html#proxyrequests">ProxyRequests</a></code>, this | |
| triggers the needed treatment of requests when HTTP/2 is enabled | |
| in a forward proxy configuration. Both directive should be enabled. | |
| </p><p> | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2push"><span id="H2Push">H2Push</span> Directive <a title="Permanent link" href="#h2push" class="permalink">¶</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 <a href="https://www.rfc-editor.org/rfc/rfc8288">RFC 8288</a> for the | |
| specification of Web Linking). 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 id="h2pushdiarysize"><span id="H2PushDiarySize">H2PushDiarySize</span> Directive <a title="Permanent link" href="#h2pushdiarysize" class="permalink">¶</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 <var>n</var></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 id="h2pushpriority"><span id="H2PushPriority">H2PushPriority</span> Directive <a title="Permanent link" href="#h2pushpriority" class="permalink">¶</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 <var>mime-type</var> [after|before|interleaved] [<var>weight</var>]</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 id="h2pushresource"><span id="H2PushResource">H2PushResource</span> Directive <a title="Permanent link" href="#h2pushresource" class="permalink">¶</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] <var>path</var> [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#Override">Override:</a></th><td>FileInfo</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 id="h2serializeheaders"><span id="H2SerializeHeaders">H2SerializeHeaders</span> Directive <a title="Permanent link" href="#h2serializeheaders" class="permalink">¶</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 id="h2streammaxmemsize"><span id="H2StreamMaxMemSize">H2StreamMaxMemSize</span> Directive <a title="Permanent link" href="#h2streammaxmemsize" class="permalink">¶</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 <var>bytes</var></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 id="h2streamtimeout"><span id="H2StreamTimeout">H2StreamTimeout</span> Directive <a title="Permanent link" href="#h2streamtimeout" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum time waiting when sending/receiving data to stream processing</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2StreamTimeout <var>time-interval</var>[s]</code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>Value of <code class="directive"><a href="../mod/core.html#timeout">Timeout</a></code></code></td></tr> | |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| <code class="directive">H2StreamTimeout</code> specifies the maximum time that | |
| a stream being processed will wait for its data to be sent/received. | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2tlscooldownsecs"><span id="H2TLSCoolDownSecs">H2TLSCoolDownSecs</span> Directive <a title="Permanent link" href="#h2tlscooldownsecs" class="permalink">¶</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 <var>seconds</var></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 id="h2tlswarmupsize"><span id="H2TLSWarmUpSize">H2TLSWarmUpSize</span> Directive <a title="Permanent link" href="#h2tlswarmupsize" class="permalink">¶</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 <var>amount</var></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 id="h2upgrade"><span id="H2Upgrade">H2Upgrade</span> Directive <a title="Permanent link" href="#h2upgrade" class="permalink">¶</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 id="h2websockets"><span id="H2WebSockets">H2WebSockets</span> Directive <a title="Permanent link" href="#h2websockets" class="permalink">¶</a></h2> | |
| <table class="directive"> | |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>En-/Disable WebSockets via HTTP/2</td></tr> | |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>H2WebSockets on|off</code></td></tr> | |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>H2WebSockets 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 2.5.1 and later.</td></tr> | |
| </table> | |
| <p> | |
| Use <code class="directive">H2WebSockets</code> to enable or disable | |
| bootstrapping of WebSockets via the HTTP/2 protocol. This | |
| protocol extension is defined in RFC 8441. | |
| </p><p> | |
| Such requests come as a CONNECT with an extra ':protocol' | |
| header. Such requests are transformed inside the module to | |
| their HTTP/1.1 equivalents before passing it to internal | |
| processing. | |
| </p><p> | |
| This means that HTTP/2 WebSockets can be used for a | |
| <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> with | |
| 'upgrade=websocket' parameter without further changes. | |
| </p><p> | |
| For (3rd party) modules that handle WebSockets directly in the | |
| server, the protocol bootstrapping itself will also work. However | |
| the transfer of data does require extra support in case of HTTP/2. | |
| The negotiated WebSocket will not be able to use the client connection | |
| socket for polling IO related events. | |
| </p><p> | |
| Because enabling this feature might break backward compatibility | |
| for such 3rd party modules, it is not enabled by default. | |
| </p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="h2windowsize"><span id="H2WindowSize">H2WindowSize</span> Directive <a title="Permanent link" href="#h2windowsize" class="permalink">¶</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 <var>bytes</var></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> | |
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