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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 06:33:50 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 06:33:50 +0000
commitfe39ffb8b90ae4e002ed73fe98617cd590abb467 (patch)
treeb80e5956907d8aeaaffe4e4f0c068c0e6157ce8b /docs/manual/vhosts/details.html.en
parentInitial commit. (diff)
downloadapache2-fe39ffb8b90ae4e002ed73fe98617cd590abb467.tar.xz
apache2-fe39ffb8b90ae4e002ed73fe98617cd590abb467.zip
Adding upstream version 2.4.56.upstream/2.4.56upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<?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>An In-Depth Discussion of Virtual Host Matching - 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 id="manual-page"><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="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
+<div id="path">
+<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.4</a> &gt; <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>An In-Depth Discussion of Virtual Host Matching</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
+</div>
+
+
+ <p>This document attempts to explain
+ exactly what Apache HTTP Server does when deciding what virtual host to
+ serve a request from.</p>
+
+ <p>Most users should read about <a href="name-based.html#namevip">
+ Name-based vs. IP-based Virtual Hosts</a> to decide which type they
+ want to use, then read more about <a href="name-based.html">name-based</a>
+ or <a href="ip-based.html">IP-based</a> virtualhosts, and then see
+ <a href="examples.html">some examples</a>.</p>
+
+ <p>If you want to understand all the details, then you can
+ come back to this page.</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><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#configparsing">Configuration File</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#hostmatching">Virtual Host Matching</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#tips">Tips</a></li>
+</ul><h3>See also</h3><ul class="seealso"><li><a href="ip-based.html">IP-based Virtual Host Support</a></li><li><a href="name-based.html">Name-based Virtual Hosts Support</a></li><li><a href="examples.html">Virtual Host examples for common setups</a></li><li><a href="mass.html">Dynamically configured mass virtual hosting</a></li><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="configparsing" id="configparsing">Configuration File</a></h2>
+
+ <p>There is a <em>main server</em> which consists of all the
+ definitions appearing outside of
+ <code>&lt;VirtualHost&gt;</code> sections.</p>
+
+ <p>There are virtual
+ servers, called <em>vhosts</em>, which are defined by
+ <code class="directive"><a href="../mod/core.html#virtualhost">&lt;VirtualHost&gt;</a></code>
+ sections.</p>
+
+ <p>Each <code>VirtualHost</code> directive includes one
+ or more addresses and optional ports.</p>
+
+ <p>Hostnames can be used in place of IP addresses in a virtual
+ host definition, but they are resolved at startup and if any name
+ resolutions fail, those virtual host definitions are ignored.
+ This is, therefore, not recommended.</p>
+
+ <p>The address can be specified as
+ <code>*</code>, which will match a request if no
+ other vhost has the explicit address on which the request was
+ received. </p>
+
+ <p>The address appearing in the <code>VirtualHost</code>
+ directive can have an optional port. If the port is unspecified,
+ it is treated as a wildcard port, which can also be indicated
+ explicitly using <code>*</code>.
+ The wildcard port matches any port.</p>
+
+ <p>(Port numbers specified in the <code>VirtualHost</code> directive do
+ not influence what port numbers Apache will listen on, they only control
+ which <code>VirtualHost</code> will be selected to handle a request.
+ Use the <code class="directive"><a href="../mod/mpm_common.html#listen">Listen</a></code> directive to
+ control the addresses and ports on which the server listens.)
+ </p>
+
+ <p>Collectively the
+ entire set of addresses (including multiple
+ results from DNS lookups) are called the vhost's
+ <em>address set</em>.</p>
+
+ <p>Apache automatically discriminates on the
+ basis of the HTTP <code>Host</code> header supplied by the client
+ whenever the most specific match for an IP address and port combination
+ is listed in multiple virtual hosts.</p>
+
+ <p>The
+ <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> directive
+ may appear anywhere within the definition of a server. However,
+ each appearance overrides the previous appearance (within that
+ server). If no <code>ServerName</code> is specified, the server
+ attempts to deduce it from the server's IP address.</p>
+
+ <p>The first name-based vhost in the configuration file for a
+ given IP:port pair is significant because it is used for all
+ requests received on that address and port for which no other
+ vhost for that IP:port pair has a matching ServerName or
+ ServerAlias. It is also used for all SSL connections if the
+ server does not support <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>.</p>
+
+ <p>The complete list of names in the <code>VirtualHost</code>
+ directive are treated just like a (non wildcard) <code>ServerAlias</code>
+ (but are not overridden by any <code>ServerAlias</code> statement).</p>
+
+ <p>For every vhost various default values are set. In
+ particular:</p>
+
+ <ol>
+ <li>If a vhost has no <code class="directive"><a href="../mod/core.html#serveradmin">ServerAdmin</a></code>,
+ <code class="directive"><a href="../mod/core.html#timeout">Timeout</a></code>,
+ <code class="directive"><a href="../mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code>,
+ <code class="directive"><a href="../mod/core.html#keepalive">KeepAlive</a></code>,
+ <code class="directive"><a href="../mod/core.html#maxkeepaliverequests">MaxKeepAliveRequests</a></code>,
+ <code class="directive"><a href="../mod/mpm_common.html#receivebuffersize">ReceiveBufferSize</a></code>,
+ or <code class="directive"><a href="../mod/mpm_common.html#sendbuffersize">SendBufferSize</a></code>
+ directive then the respective value is inherited from the
+ main server. (That is, inherited from whatever the final
+ setting of that value is in the main server.)</li>
+
+ <li>The "lookup defaults" that define the default directory
+ permissions for a vhost are merged with those of the
+ main server. This includes any per-directory configuration
+ information for any module.</li>
+
+ <li>The per-server configs for each module from the
+ main server are merged into the vhost server.</li>
+ </ol>
+
+ <p>Essentially, the main server is treated as "defaults" or a
+ "base" on which to build each vhost. But the positioning of
+ these main server definitions in the config file is largely
+ irrelevant -- the entire config of the main server has been
+ parsed when this final merging occurs. So even if a main server
+ definition appears after a vhost definition it might affect the
+ vhost definition.</p>
+
+ <p>If the main server has no <code>ServerName</code> at this
+ point, then the hostname of the machine that <code class="program"><a href="../programs/httpd.html">httpd</a></code>
+ is running on is used instead. We will call the <em>main server address
+ set</em> those IP addresses returned by a DNS lookup on the
+ <code>ServerName</code> of the main server.</p>
+
+ <p>For any undefined <code>ServerName</code> fields, a
+ name-based vhost defaults to the address given first in the
+ <code>VirtualHost</code> statement defining the vhost.</p>
+
+ <p>Any vhost that includes the magic <code>_default_</code>
+ wildcard is given the same <code>ServerName</code> as the
+ main server.</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="hostmatching" id="hostmatching">Virtual Host Matching</a></h2>
+
+ <p>The server determines which vhost to use for a request as
+ follows:</p>
+
+ <h3><a name="hashtable" id="hashtable">IP address lookup</a></h3>
+
+ <p>When the connection is first received on some address and port,
+ the server looks for all the <code>VirtualHost</code> definitions
+ that have the same IP address and port.</p>
+
+ <p>If there are no exact matches for the address and port, then
+ wildcard (<code>*</code>) matches are considered.</p>
+
+ <p>If no matches are found, the request is served by the
+ main server.</p>
+
+ <p>If there are <code>VirtualHost</code> definitions for
+ the IP address, the next step is to decide if we have to
+ deal with an IP-based or a name-based vhost.</p>
+
+
+
+ <h3><a name="ipbased" id="ipbased">IP-based vhost</a></h3>
+
+ <p>If there is exactly one <code>VirtualHost</code> directive
+ listing the IP address and port combination that was determined
+ to be the best match, no further actions are performed and
+ the request is served from the matching vhost.</p>
+
+
+
+ <h3><a name="namebased" id="namebased">Name-based vhost</a></h3>
+
+ <p>If there are multiple <code>VirtualHost</code> directives listing
+ the IP address and port combination that was determined to be the
+ best match, the "list" in the remaining steps refers to the list of vhosts
+ that matched, in the order they were in the configuration file.</p>
+
+ <p>If the connection is using SSL, the server supports <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>, and
+ the SSL client handshake includes the TLS extension with the
+ requested hostname, then that hostname is used below just like the
+ <code>Host:</code> header would be used on a non-SSL connection.
+ Otherwise, the first name-based vhost whose address matched is
+ used for SSL connections. This is significant because the
+ vhost determines which certificate the server will use for the
+ connection.</p>
+
+ <p>If the request contains a <code>Host:</code> header field, the
+ list is searched for the first vhost with a matching
+ <code>ServerName</code> or <code>ServerAlias</code>, and the
+ request is served from that vhost. A <code>Host:</code> header
+ field can contain a port number, but Apache always ignores it and
+ matches against the real port to which the client sent the
+ request.</p>
+
+ <p>The first vhost in the config
+ file with the specified IP address has the highest priority
+ and catches any request to an unknown server name, or a request
+ without a <code>Host:</code> header field (such as a HTTP/1.0
+ request).</p>
+
+
+
+ <h3><a name="persistent" id="persistent">Persistent connections</a></h3>
+
+ <p>The <em>IP lookup</em> described above is only done <em>once</em> for a
+ particular TCP/IP session while the <em>name lookup</em> is done on
+ <em>every</em> request during a KeepAlive/persistent
+ connection. In other words, a client may request pages from
+ different name-based vhosts during a single persistent
+ connection.</p>
+
+
+
+ <h3><a name="absoluteURI" id="absoluteURI">Absolute URI</a></h3>
+
+ <p>If the URI from the request is an absolute URI, and its
+ hostname and port match the main server or one of the
+ configured virtual hosts <em>and</em> match the address and
+ port to which the client sent the request, then the
+ scheme/hostname/port prefix is stripped off and the remaining
+ relative URI is served by the corresponding main server or
+ virtual host. If it does not match, then the URI remains
+ untouched and the request is taken to be a proxy request.</p>
+
+
+<h3><a name="observations" id="observations">Observations</a></h3>
+
+ <ul>
+ <li>Name-based virtual hosting is a process applied after
+ the server has selected the best matching IP-based virtual
+ host.</li>
+
+ <li>If you don't care what IP address the client has connected to, use a
+ "*" as the address of every virtual host, and name-based virtual hosting
+ is applied across all configured virtual hosts.</li>
+
+ <li><code>ServerName</code> and <code>ServerAlias</code>
+ checks are never performed for an IP-based vhost.</li>
+
+ <li>Only the ordering of
+ name-based vhosts for a specific address set is significant.
+ The one name-based vhosts that comes first in the
+ configuration file has the highest priority for its
+ corresponding address set.</li>
+
+ <li>Any port in the <code>Host:</code> header field is never used during the
+ matching process. Apache always uses the real port to which
+ the client sent the request.</li>
+
+ <li>If two vhosts have an address in common, those common addresses
+ act as name-based virtual hosts implicitly. This is new behavior as of
+ 2.3.11.</li>
+
+ <li>The main server is only used to serve a request if the IP
+ address and port number to which the client connected
+ does not match any vhost (including a
+ <code>*</code> vhost). In other words, the main server
+ only catches a request for an unspecified address/port
+ combination (unless there is a <code>_default_</code> vhost
+ which matches that port).</li>
+
+ <li>You should never specify DNS names in
+ <code>VirtualHost</code> directives because it will force
+ your server to rely on DNS to boot. Furthermore it poses a
+ security threat if you do not control the DNS for all the
+ domains listed. There's <a href="../dns-caveats.html">more
+ information</a> available on this and the next two
+ topics.</li>
+
+ <li><code>ServerName</code> should always be set for each
+ vhost. Otherwise a DNS lookup is required for each
+ vhost.</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="tips" id="tips">Tips</a></h2>
+
+ <p>In addition to the tips on the <a href="../dns-caveats.html#tips">DNS Issues</a> page, here are
+ some further tips:</p>
+
+ <ul>
+ <li>Place all main server definitions before any
+ <code>VirtualHost</code> definitions. (This is to aid the
+ readability of the configuration -- the post-config merging
+ process makes it non-obvious that definitions mixed in around
+ virtual hosts might affect all virtual hosts.)</li>
+ </ul>
+
+</div></div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</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&amp;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. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
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