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443 lines
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HTML
443 lines
16 KiB
HTML
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Dynamically configured mass virtual hosting</title>
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</head>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
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vlink="#000080" alink="#FF0000">
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">Dynamically configured mass virtual
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hosting</h1>
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<p>This document describes how to efficiently serve an
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arbitrary number of virtual hosts with Apache 1.3. <!--
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Written by Tony Finch (fanf@demon.net) (dot@dotat.at).
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Some examples were derived from Ralf S. Engleschall's document
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http://www.engelschall.com/pw/apache/rewriteguide/
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Some suggestions were made by Brian Behlendorf.
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-->
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</p>
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<h2><a id="contents" name="contents">Contents:</a></h2>
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<ul>
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<li><a href="#motivation">Motivation</a></li>
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<li><a href="#overview">Overview</a></li>
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<li><a href="#simple">Simple dynamic virtual hosts</a></li>
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<li><a href="#homepages">A virtually hosted homepages
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system</a></li>
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<li><a href="#combinations">Using more than one virtual
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hosting system on the same server</a></li>
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<li><a href="#ipbased">More efficient IP-based virtual
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hosting</a></li>
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<li><a href="#oldversion">Using older versions of
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Apache</a></li>
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<li><a href="#simple.rewrite">Simple dynamic virtual hosts
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using <code>mod_rewrite</code></a></li>
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<li><a href="#homepages.rewrite">A homepages system using
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<code>mod_rewrite</code></a></li>
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<li><a href="#xtra-conf">Using a separate virtual host
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configuration file</a></li>
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</ul>
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<hr />
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<h2><a id="motivation" name="motivation">Motivation</a></h2>
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<p>The techniques described here are of interest if your
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<code>httpd.conf</code> contains many
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<code><VirtualHost></code> sections that are
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substantially the same, for example:</p>
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<pre>
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NameVirtualHost 111.22.33.44
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<VirtualHost 111.22.33.44>
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ServerName www.customer-1.com
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DocumentRoot /www/hosts/www.customer-1.com/docs
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ScriptAlias /cgi-bin/ /www/hosts/www.customer-1.com/cgi-bin
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</VirtualHost>
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<VirtualHost 111.22.33.44>
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ServerName www.customer-2.com
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DocumentRoot /www/hosts/www.customer-2.com/docs
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ScriptAlias /cgi-bin/ /www/hosts/www.customer-2.com/cgi-bin
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</VirtualHost>
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# blah blah blah
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<VirtualHost 111.22.33.44>
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ServerName www.customer-N.com
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DocumentRoot /www/hosts/www.customer-N.com/docs
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ScriptAlias /cgi-bin/ /www/hosts/www.customer-N.com/cgi-bin
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</VirtualHost>
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</pre>
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<br />
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<br />
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<p>The basic idea is to replace all of the static
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<code><VirtualHost></code> configuration with a mechanism
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that works it out dynamically. This has a number of
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advantages:</p>
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<ol>
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<li>Your configuration file is smaller so Apache starts
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faster and uses less memory.</li>
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<li>Adding virtual hosts is simply a matter of creating the
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appropriate directories in the filesystem and entries in the
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DNS - you don't need to reconfigure or restart Apache.</li>
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</ol>
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<br />
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<br />
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<p>The main disadvantage is that you cannot have a different
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log file for each virtual host; however if you have very many
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virtual hosts then doing this is dubious anyway because it eats
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file descriptors. It is better to log to a pipe or a fifo and
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arrange for the process at the other end to distribute the logs
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to the customers (it can also accumulate statistics, etc.).</p>
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<hr />
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<h2><a id="overview" name="overview">Overview</a></h2>
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<p>A virtual host is defined by two pieces of information: its
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IP address, and the contents of the <code>Host:</code> header
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in the HTTP request. The dynamic mass virtual hosting technique
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is based on automatically inserting this information into the
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pathname of the file that is used to satisfy the request. This
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is done most easily using <a
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href="../mod/mod_vhost_alias.html"><code>mod_vhost_alias</code></a>,
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but if you are using a version of Apache up to 1.3.6 then you
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must use <a
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href="../mod/mod_rewrite.html"><code>mod_rewrite</code></a>.
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Both of these modules are disabled by default; you must enable
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one of them when configuring and building Apache if you want to
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use this technique.</p>
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<p>A couple of things need to be `faked' to make the dynamic
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virtual host look like a normal one. The most important is the
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server name which is used by Apache to generate
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self-referential URLs, etc. It is configured with the
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<code>ServerName</code> directive, and it is available to CGIs
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via the <code>SERVER_NAME</code> environment variable. The
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actual value used at run time is controlled by the <a
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href="../mod/core.html#usecanonicalname"><code>UseCanonicalName</code></a>
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setting. With <code>UseCanonicalName Off</code> the server name
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comes from the contents of the <code>Host:</code> header in the
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request. With <code>UseCanonicalName DNS</code> it comes from a
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reverse DNS lookup of the virtual host's IP address. The former
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setting is used for name-based dynamic virtual hosting, and the
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latter is used for IP-based hosting. If Apache cannot work out
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the server name because there is no <code>Host:</code> header
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or the DNS lookup fails then the value configured with
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<code>ServerName</code> is used instead.</p>
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<p>The other thing to `fake' is the document root (configured
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with <code>DocumentRoot</code> and available to CGIs via the
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<code>DOCUMENT_ROOT</code> environment variable). In a normal
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configuration this setting is used by the core module when
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mapping URIs to filenames, but when the server is configured to
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do dynamic virtual hosting that job is taken over by another
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module (either <code>mod_vhost_alias</code> or
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<code>mod_rewrite</code>) which has a different way of doing
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the mapping. Neither of these modules is responsible for
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setting the <code>DOCUMENT_ROOT</code> environment variable so
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if any CGIs or SSI documents make use of it they will get a
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misleading value.</p>
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<hr />
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<h2><a id="simple" name="simple">Simple dynamic virtual
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hosts</a></h2>
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<p>This extract from <code>httpd.conf</code> implements the
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virtual host arrangement outlined in the <a
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href="#motivation">Motivation</a> section above, but in a
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generic fashion using <code>mod_vhost_alias</code>.</p>
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<pre>
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# get the server name from the Host: header
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UseCanonicalName Off
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# this log format can be split per-virtual-host based on the first field
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LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon
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CustomLog logs/access_log vcommon
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# include the server name in the filenames used to satisfy requests
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VirtualDocumentRoot /www/hosts/%0/docs
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VirtualScriptAlias /www/hosts/%0/cgi-bin
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</pre>
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<p>This configuration can be changed into an IP-based virtual
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hosting solution by just turning <code>UseCanonicalName
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Off</code> into <code>UseCanonicalName DNS</code>. The server
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name that is inserted into the filename is then derived from
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the IP address of the virtual host.</p>
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<hr />
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<h2><a id="homepages" name="homepages">A virtually hosted
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homepages system</a></h2>
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<p>This is an adjustment of the above system tailored for an
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ISP's homepages server. Using a slightly more complicated
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configuration we can select substrings of the server name to
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use in the filename so that e.g. the documents for
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<samp>www.user.isp.com</samp> are found in
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<code>/home/user/</code>. It uses a single <code>cgi-bin</code>
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directory instead of one per virtual host.</p>
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<pre>
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# all the preliminary stuff is the same as above, then
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# include part of the server name in the filenames
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VirtualDocumentRoot /www/hosts/%2/docs
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# single cgi-bin directory
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ScriptAlias /cgi-bin/ /www/std-cgi/
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</pre>
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<p>There are examples of more complicated
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<code>VirtualDocumentRoot</code> settings in <a
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href="../mod/mod_vhost_alias.html">the
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<code>mod_vhost_alias</code> documentation</a>.</p>
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<hr />
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<h2><a id="combinations" name="combinations">Using more than
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one virtual hosting system on the same server</a></h2>
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<p>With more complicated setups you can use Apache's normal
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<code><VirtualHost></code> directives to control the
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scope of the various virtual hosting configurations. For
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example, you could have one IP address for homepages customers
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and another for commercial customers with the following setup.
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This can of course be combined with conventional
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<code><VirtualHost></code> configuration sections.</p>
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<pre>
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UseCanonicalName Off
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LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon
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<Directory /www/commercial>
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Options FollowSymLinks
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AllowOverride All
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</Directory>
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<Directory /www/homepages>
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Options FollowSymLinks
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AllowOverride None
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</Directory>
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<VirtualHost 111.22.33.44>
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ServerName www.commercial.isp.com
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CustomLog logs/access_log.commercial vcommon
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VirtualDocumentRoot /www/commercial/%0/docs
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VirtualScriptAlias /www/commercial/%0/cgi-bin
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</VirtualHost>
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<VirtualHost 111.22.33.45>
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ServerName www.homepages.isp.com
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CustomLog logs/access_log.homepages vcommon
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VirtualDocumentRoot /www/homepages/%0/docs
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ScriptAlias /cgi-bin/ /www/std-cgi/
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</VirtualHost>
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</pre>
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<hr />
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<h2><a id="ipbased" name="ipbased">More efficient IP-based
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virtual hosting</a></h2>
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<p>After <a href="#simple">the first example</a> I noted that
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it is easy to turn it into an IP-based virtual hosting setup.
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Unfortunately that configuration is not very efficient because
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it requires a DNS lookup for every request. This can be avoided
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by laying out the filesystem according to the IP addresses
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themselves rather than the corresponding names and changing the
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logging similarly. Apache will then usually not need to work
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out the server name and so incur a DNS lookup.</p>
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<pre>
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# get the server name from the reverse DNS of the IP address
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UseCanonicalName DNS
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# include the IP address in the logs so they may be split
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LogFormat "%A %h %l %u %t \"%r\" %s %b" vcommon
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CustomLog logs/access_log vcommon
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# include the IP address in the filenames
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VirtualDocumentRootIP /www/hosts/%0/docs
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VirtualScriptAliasIP /www/hosts/%0/cgi-bin
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</pre>
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<hr />
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<h2><a id="oldversion" name="oldversion">Using older versions
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of Apache</a></h2>
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<p>The examples above rely on <code>mod_vhost_alias</code>
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which appeared after version 1.3.6. If you are using a version
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of Apache without <code>mod_vhost_alias</code> then you can
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implement this technique with <code>mod_rewrite</code> as
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illustrated below, but only for Host:-header-based virtual
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hosts.</p>
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<p>In addition there are some things to beware of with logging.
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Apache 1.3.6 is the first version to include the
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<code>%V</code> log format directive; in versions 1.3.0 - 1.3.3
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the <code>%v</code> option did what <code>%V</code> does;
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version 1.3.4 has no equivalent. In all these versions of
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Apache the <code>UseCanonicalName</code> directive can appear
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in <code>.htaccess</code> files which means that customers can
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cause the wrong thing to be logged. Therefore the best thing to
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do is use the <code>%{Host}i</code> directive which logs the
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<code>Host:</code> header directly; note that this may include
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<code>:port</code> on the end which is not the case for
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<code>%V</code>.</p>
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<hr />
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<h2><a id="simple.rewrite" name="simple.rewrite">Simple dynamic
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virtual hosts using <code>mod_rewrite</code></a></h2>
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<p>This extract from <code>httpd.conf</code> does the same
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thing as <a href="#simple">the first example</a>. The first
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half is very similar to the corresponding part above but with
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some changes for backward compatibility and to make the
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<code>mod_rewrite</code> part work properly; the second half
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configures <code>mod_rewrite</code> to do the actual work.</p>
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<p>There are a couple of especially tricky bits: By default,
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<code>mod_rewrite</code> runs before the other URI translation
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modules (<code>mod_alias</code> etc.) so if they are used then
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<code>mod_rewrite</code> must be configured to accommodate
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them. Also, mome magic must be performed to do a
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per-dynamic-virtual-host equivalent of
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<code>ScriptAlias</code>.</p>
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<pre>
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# get the server name from the Host: header
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UseCanonicalName Off
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# splittable logs
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LogFormat "%{Host}i %h %l %u %t \"%r\" %s %b" vcommon
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CustomLog logs/access_log vcommon
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<Directory /www/hosts>
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# ExecCGI is needed here because we can't force
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# CGI execution in the way that ScriptAlias does
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Options FollowSymLinks ExecCGI
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</Directory>
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# now for the hard bit
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RewriteEngine On
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# a ServerName derived from a Host: header may be any case at all
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RewriteMap lowercase int:tolower
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## deal with normal documents first:
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# allow Alias /icons/ to work - repeat for other aliases
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RewriteCond %{REQUEST_URI} !^/icons/
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# allow CGIs to work
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RewriteCond %{REQUEST_URI} !^/cgi-bin/
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# do the magic
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RewriteRule ^/(.*)$ /www/hosts/${lowercase:%{SERVER_NAME}}/docs/$1
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## and now deal with CGIs - we have to force a MIME type
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RewriteCond %{REQUEST_URI} ^/cgi-bin/
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RewriteRule ^/(.*)$ /www/hosts/${lowercase:%{SERVER_NAME}}/cgi-bin/$1 [T=application/x-httpd-cgi]
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# that's it!
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</pre>
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<hr />
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<h2><a id="homepages.rewrite" name="homepages.rewrite">A
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homepages system using <code>mod_rewrite</code></a></h2>
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<p>This does the same thing as <a href="#homepages">the second
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example</a>.</p>
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<pre>
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RewriteEngine on
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RewriteMap lowercase int:tolower
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# allow CGIs to work
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RewriteCond %{REQUEST_URI} !^/cgi-bin/
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# check the hostname is right so that the RewriteRule works
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RewriteCond ${lowercase:%{SERVER_NAME}} ^www\.[a-z-]+\.isp\.com$
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# concatenate the virtual host name onto the start of the URI
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# the [C] means do the next rewrite on the result of this one
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RewriteRule ^(.+) ${lowercase:%{SERVER_NAME}}$1 [C]
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# now create the real file name
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RewriteRule ^www\.([a-z-]+)\.isp\.com/(.*) /home/$1/$2
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# define the global CGI directory
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ScriptAlias /cgi-bin/ /www/std-cgi/
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</pre>
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<hr />
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<h2><a id="xtra-conf" name="xtra-conf">Using a separate virtual
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host configuration file</a></h2>
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<p>This arrangement uses more advanced <code>mod_rewrite</code>
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features to get the translation from virtual host to document
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root from a separate configuration file. This provides more
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flexibility but requires more complicated configuration.</p>
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<p>The <code>vhost.map</code> file contains something like
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this:</p>
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<pre>
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www.customer-1.com /www/customers/1
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www.customer-2.com /www/customers/2
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# ...
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www.customer-N.com /www/customers/N
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</pre>
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<br />
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<br />
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<p>The <code>http.conf</code> contains this:</p>
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<pre>
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RewriteEngine on
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RewriteMap lowercase int:tolower
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# define the map file
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RewriteMap vhost txt:/www/conf/vhost.map
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# deal with aliases as above
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RewriteCond %{REQUEST_URI} !^/icons/
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RewriteCond %{REQUEST_URI} !^/cgi-bin/
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RewriteCond ${lowercase:%{SERVER_NAME}} ^(.+)$
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# this does the file-based remap
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RewriteCond ${vhost:%1} ^(/.*)$
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RewriteRule ^/(.*)$ %1/docs/$1
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RewriteCond %{REQUEST_URI} ^/cgi-bin/
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RewriteCond ${lowercase:%{SERVER_NAME}} ^(.+)$
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RewriteCond ${vhost:%1} ^(/.*)$
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RewriteRule ^/(.*)$ %1/cgi-bin/$1
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</pre>
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<br />
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<br />
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<!--#include virtual="footer.html" -->
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</body>
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</html>
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