| <?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="<-" 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="./">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"> en </a> | |
| <a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </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><VirtualHost></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"><VirtualHost></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"> en </a> | |
| <a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </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. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div> |
| <script type="text/javascript"><!--//--><![CDATA[//><!-- |
| var comments_shortname = 'httpd'; |
| var comments_identifier = 'http://httpd.apache.org/docs/2.4/vhosts/details.html'; |
| (function(w, d) { |
| if (w.location.hostname.toLowerCase() == "httpd.apache.org") { |
| d.write('<div id="comments_thread"><\/div>'); |
| var s = d.createElement('script'); |
| s.type = 'text/javascript'; |
| s.async = true; |
| s.src = 'https://comments.apache.org/show_comments.lua?site=' + comments_shortname + '&page=' + comments_identifier; |
| (d.getElementsByTagName('head')[0] || d.getElementsByTagName('body')[0]).appendChild(s); |
| } |
| else { |
| d.write('<div id="comments_thread">Comments are disabled for this page at the moment.<\/div>'); |
| } |
| })(window, document); |
| //--><!]]></script></div><div id="footer"> |
| <p class="apache">Copyright 2021 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> |
| <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></div><script type="text/javascript"><!--//--><![CDATA[//><!-- |
| if (typeof(prettyPrint) !== 'undefined') { |
| prettyPrint(); |
| } |
| //--><!]]></script> |
| </body></html> |