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-<title>Dynamically configured mass virtual hosting - Apache HTTP Server</title>
+<title>Dynamically Configured Mass Virtual Hosting - Apache HTTP Server</title>
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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 2.3</a> > <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>Dynamically configured mass virtual hosting</h1>
+<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 2.3</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>
<p>This document describes how to efficiently serve an
- arbitrary number of virtual hosts with Apache.
+ 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 more than
- one virtual hosting system 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="#oldversion">Using older versions of Apache</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#simple.rewrite">Simple dynamic
- virtual hosts using <code>mod_rewrite</code></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>
+ 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">
</code></p></div>
<p>The basic idea is to replace all of the static
- <code><VirtualHost></code> configuration with a mechanism
- that works it out dynamically. This has a number of
+ <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
- faster and uses less memory.</li>
+ <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 very many
- virtual hosts then doing this is dubious anyway because it eats
- file descriptors. 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 (it can also accumulate statistics, etc.).</p>
+ <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">
<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
- is based on automatically inserting this information into the
+ used here is based on automatically inserting this information into the
pathname of the file that is used to satisfy the request. This
- is done most easily using <code class="module"><a href="../mod/mod_vhost_alias.html">mod_vhost_alias</a></code>,
- but if you are using a version of Apache up to 1.3.6 then you
- must use <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
+ 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
+ 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
- comes from the contents of the <code>Host:</code> header in the
- request. With <code>UseCanonicalName DNS</code> it comes from a
+ 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
+ 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 setting is used by the core module when
+ 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 is taken over by another
+ 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
+ <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
+ 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>
+<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
</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>
+<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
+ <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 e.g. the documents for
+ 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><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 more than
- one virtual hosting system on the same server</a></h2>
+<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
+ <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 homepages customers
- and another for commercial customers with the following setup.
- This can of course be combined with conventional
+ 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
<code><VirtualHost></code> configuration sections.</p>
<div class="example"><p><code>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
-<h2><a name="ipbased" id="ipbased">More efficient IP-based virtual hosting</a></h2>
+<h2><a name="ipbased" id="ipbased">More Efficient IP-Based Virtual Hosting</a></h2>
- <p>After <a href="#simple">the first example</a> I noted that
- it is easy to turn it into an IP-based virtual hosting setup.
- Unfortunately that configuration is not very efficient because
- it requires a DNS lookup for every request. This can be avoided
- by laying out the filesystem according to the IP addresses
- themselves rather than the corresponding names and changing the
- logging similarly. Apache will then usually not need to work
- out the server name and so incur a DNS lookup.</p>
+ <p>The configuration changes suggested to turn <a href="#simple">the first
+ example</a> into an IP-based virtual hosting setup result in
+ a rather inefficient setup. A new DNS lookup is required for every
+ request. To avoid this overhead, the filesystem can be arranged to
+ correspond to the IP addresses, instead of to the host names, thereby
+ negating the need for a DNS lookup. Logging will also have to be adjusted
+ to fit this system.</p>
<div class="example"><p><code>
# get the server name from the reverse DNS of the IP address<br />
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
-<h2><a name="oldversion" id="oldversion">Using older versions of Apache</a></h2>
-
- <p>The examples above rely on <code>mod_vhost_alias</code>
- which appeared after version 1.3.6. If you are using a version
- of Apache without <code>mod_vhost_alias</code> then you can
- implement this technique with <code>mod_rewrite</code> as
- illustrated below, but only for Host:-header-based virtual
- hosts.</p>
-
- <p>In addition there are some things to beware of with logging.
- Apache 1.3.6 is the first version to include the
- <code>%V</code> log format directive; in versions 1.3.0 - 1.3.3
- the <code>%v</code> option did what <code>%V</code> does;
- version 1.3.4 has no equivalent. In all these versions of
- Apache the <code>UseCanonicalName</code> directive can appear
- in <code>.htaccess</code> files which means that customers can
- cause the wrong thing to be logged. Therefore the best thing to
- do is use the <code>%{Host}i</code> directive which logs the
- <code>Host:</code> header directly; note that this may include
- <code>:port</code> on the end which is not the case for
- <code>%V</code>.</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.rewrite" id="simple.rewrite">Simple dynamic
- virtual hosts using <code>mod_rewrite</code></a></h2>
+<h2><a name="simple.rewrite" id="simple.rewrite">Simple Dynamic
+ Virtual Hosts Using <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code></a></h2>
<p>This extract from <code>httpd.conf</code> does the same
thing as <a href="#simple">the first example</a>. The first
- half is very similar to the corresponding part above but with
- some changes for backward compatibility and to make the
+ half is very similar to the corresponding part above, except for
+ some changes, required for backward compatibility and to make the
<code>mod_rewrite</code> part work properly; the second half
configures <code>mod_rewrite</code> to do the actual work.</p>
- <p>There are a couple of especially tricky bits: By default,
- <code>mod_rewrite</code> runs before the other URI translation
- modules (<code>mod_alias</code> etc.) so if they are used then
- <code>mod_rewrite</code> must be configured to accommodate
- them. Also, some magic must be performed to do a
+ <p>There are a couple of especially tricky bits: by default,
+ <code>mod_rewrite</code> runs before other URI translation
+ modules (<code>mod_alias</code> etc.) - so if you wish to use these modules, <code>mod_rewrite</code> must be configured to accommodate
+ them. Also, some magic is required to do a
per-dynamic-virtual-host equivalent of
<code>ScriptAlias</code>.</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.rewrite" id="homepages.rewrite">A
- homepages system using <code>mod_rewrite</code></a></h2>
+ Homepages System Using <code>mod_rewrite</code></a></h2>
<p>This does the same thing as <a href="#homepages">the second
example</a>.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
-<h2><a name="xtra-conf" id="xtra-conf">Using a separate virtual
- host configuration file</a></h2>
+<h2><a name="xtra-conf" id="xtra-conf">Using a Separate Virtual
+ Host Configuration File</a></h2>
- <p>This arrangement uses more advanced <code>mod_rewrite</code>
- features to get the translation from virtual host to document
- root from a separate configuration file. This provides more
- flexibility but requires more complicated configuration.</p>
+ <p>This arrangement uses more advanced <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
+ features to work out the translation from virtual host to document
+ root, from a separate configuration file. This provides more
+ flexibility, but requires more complicated configuration.</p>
- <p>The <code>vhost.map</code> file contains something like
+ <p>The <code>vhost.map</code> file should look something like
this:</p>
<div class="example"><p><code>
www.customer-N.com /www/customers/N<br />
</code></p></div>
- <p>The <code>http.conf</code> contains this:</p>
+ <p>The <code>httpd.conf</code> should contain the following:</p>
<div class="example"><p><code>
RewriteEngine on<br />
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