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<title>Dynamically Configured Mass Virtual Hosting - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.0</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>Dynamically Configured Mass Virtual Hosting</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/vhosts/mass.html" title="English"> en </a> |
<a href="../ko/vhosts/mass.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
<p>This document describes how to efficiently serve an
arbitrary number of virtual hosts with the Apache httpd webserver.
</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#motivation">Motivation</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#overview">Overview</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#simple">Simple Dynamic Virtual Hosts</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#homepages">A Virtually Hosted Homepages System</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#combinations">Using Multiple Virtual
Hosting Systems on the Same Server</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ipbased">More Efficient IP-Based Virtual Hosting</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#simple.rewrite">Simple Dynamic
Virtual Hosts Using <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code></a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#homepages.rewrite">A
Homepages System Using <code>mod_rewrite</code></a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#xtra-conf">Using a Separate Virtual
Host Configuration File</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="motivation" id="motivation">Motivation</a></h2>
<p>The techniques described here are of interest if your
<code>httpd.conf</code> contains many
<code><VirtualHost></code> sections that are
substantially the same, for example:</p>
<div class="example"><p><code>
NameVirtualHost 111.22.33.44<br />
<VirtualHost 111.22.33.44><br />
<span class="indent">
ServerName www.customer-1.com<br />
DocumentRoot /www/hosts/www.customer-1.com/docs<br />
ScriptAlias /cgi-bin/ /www/hosts/www.customer-1.com/cgi-bin<br />
</span>
</VirtualHost><br />
<VirtualHost 111.22.33.44><br />
<span class="indent">
ServerName www.customer-2.com<br />
DocumentRoot /www/hosts/www.customer-2.com/docs<br />
ScriptAlias /cgi-bin/ /www/hosts/www.customer-2.com/cgi-bin<br />
</span>
</VirtualHost><br />
# blah blah blah<br />
<VirtualHost 111.22.33.44><br />
<span class="indent">
ServerName www.customer-N.com<br />
DocumentRoot /www/hosts/www.customer-N.com/docs<br />
ScriptAlias /cgi-bin/ /www/hosts/www.customer-N.com/cgi-bin<br />
</span>
</VirtualHost>
</code></p></div>
<p>The basic idea is to replace all of the static
<code><VirtualHost></code> configurations with a mechanism
that works them out dynamically. This has a number of
advantages:</p>
<ol>
<li>Your configuration file is smaller, so Apache starts
more quickly and uses less memory.</li>
<li>Adding virtual hosts is simply a matter of creating the
appropriate directories in the filesystem and entries in the
DNS - you don't need to reconfigure or restart Apache.</li>
</ol>
<p>The main disadvantage is that you cannot have a different log file for
each virtual host; however, if you have many virtual hosts, doing
this can be a bad idea anyway, because of the number of file
descriptors needed. It is better to log to a pipe or a fifo, and arrange for
the process at the other end to distribute the logs to the customers.
(This can also be used to accumulate statistics, etc.).</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="overview" id="overview">Overview</a></h2>
<p>A virtual host is defined by two pieces of information: its
IP address, and the contents of the <code>Host:</code> header
in the HTTP request. The dynamic mass virtual hosting technique
used here is based on automatically inserting this information into the
pathname of the file that is used to satisfy the request. This
can be most easily done by using <code class="module"><a href="../mod/mod_vhost_alias.html">mod_vhost_alias</a></code>
with Apache 2.0. Alternatively, <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> can be used.
Both of these modules are disabled by default; you must enable
one of them when configuring and building Apache if you want to
use this technique.</p>
<p>A couple of things need to be `faked' to make the dynamic
virtual host look like a normal one. The most important is the
server name, which is used by Apache to generate
self-referential URLs etc. It is configured with the
<code>ServerName</code> directive, and it is available to CGIs
via the <code>SERVER_NAME</code> environment variable. The
actual value used at run time is controlled by the <code class="directive"><a href="../mod/core.html#usecanonicalname">UseCanonicalName</a></code>
setting. With <code>UseCanonicalName Off</code>, the server name
is taken from the contents of the <code>Host:</code> header in the
request. With <code>UseCanonicalName DNS</code>, it is taken from a
reverse DNS lookup of the virtual host's IP address. The former
setting is used for name-based dynamic virtual hosting, and the
latter is used for IP-based hosting. If Apache cannot work out
the server name because there is no <code>Host:</code> header,
or the DNS lookup fails, then the value configured with
<code>ServerName</code> is used instead.</p>
<p>The other thing to `fake' is the document root (configured
with <code>DocumentRoot</code> and available to CGIs via the
<code>DOCUMENT_ROOT</code> environment variable). In a normal
configuration, this is used by the core module when
mapping URIs to filenames, but when the server is configured to
do dynamic virtual hosting, that job must be taken over by another
module (either <code>mod_vhost_alias</code> or
<code>mod_rewrite</code>), which has a different way of doing
the mapping. Neither of these modules is responsible for
setting the <code>DOCUMENT_ROOT</code> environment variable so
if any CGIs or SSI documents make use of it, they will get a
misleading value.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="simple" id="simple">Simple Dynamic Virtual Hosts</a></h2>
<p>This extract from <code>httpd.conf</code> implements the
virtual host arrangement outlined in the <a href="#motivation">Motivation</a> section above, but in a
generic fashion using <code>mod_vhost_alias</code>.</p>
<div class="example"><p><code>
# get the server name from the Host: header<br />
UseCanonicalName Off<br />
<br />
# this log format can be split per-virtual-host based on the first field<br />
LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon<br />
CustomLog logs/access_log vcommon<br />
<br />
# include the server name in the filenames used to satisfy requests<br />
VirtualDocumentRoot /www/hosts/%0/docs<br />
VirtualScriptAlias /www/hosts/%0/cgi-bin
</code></p></div>
<p>This configuration can be changed into an IP-based virtual
hosting solution by just turning <code>UseCanonicalName
Off</code> into <code>UseCanonicalName DNS</code>. The server
name that is inserted into the filename is then derived from
the IP address of the virtual host.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="homepages" id="homepages">A Virtually Hosted Homepages System</a></h2>
<p>This is an adjustment of the above system, tailored for an
ISP's homepages server. Using a slightly more complicated
configuration, we can select substrings of the server name to
use in the filename so that, for example, the documents for
<code>www.user.isp.com</code> are found in
<code>/home/user/</code>. It uses a single <code>cgi-bin</code>
directory instead of one per virtual host.</p>
<div class="example"><p><code>
# all the preliminary stuff is the same as above, then<br />
<br />
# include part of the server name in the filenames<br />
VirtualDocumentRoot /www/hosts/%2/docs<br />
<br />
# single cgi-bin directory<br />
ScriptAlias /cgi-bin/ /www/std-cgi/<br />
</code></p></div>
<p>There are examples of more complicated
<code>VirtualDocumentRoot</code> settings in the
<code class="module"><a href="../mod/mod_vhost_alias.html">mod_vhost_alias</a></code> documentation.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="combinations" id="combinations">Using Multiple Virtual
Hosting Systems on the Same Server</a></h2>
<p>With more complicated setups, you can use Apache's normal
<code><VirtualHost></code> directives to control the
scope of the various virtual hosting configurations. For
example, you could have one IP address for general customers' homepages,
and another for commercial customers, with the following setup.
This can, of course, be combined with conventional
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