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<manualpage metafile="vhosts.xml.meta">
  <parentdocument href="./">Rewrite</parentdocument>

<title>Dynamic mass virtual hosts with mod_rewrite</title>

<summary>

<p>This document supplements the <module>mod_rewrite</module> 
<a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
how you can use <module>mod_rewrite</module> to create dynamically 
configured virtual hosts.</p>

<note type="warning">mod_rewrite is not the best way to configure
virtual hosts. You should first consider the <a
href="../vhosts/mass.html">alternatives</a> before resorting to
mod_rewrite. See also the "<a href="avoid.html#vhosts">how to avoid
mod_rewrite</a> document.</note>

</summary>
<seealso><a href="../mod/mod_rewrite.html">Module documentation</a></seealso>
<seealso><a href="intro.html">mod_rewrite introduction</a></seealso>
<seealso><a href="remapping.html">Redirection and remapping</a></seealso>
<seealso><a href="access.html">Controlling access</a></seealso>
<!--<seealso><a href="vhosts.html">Virtual hosts</a></seealso>-->
<seealso><a href="proxy.html">Proxying</a></seealso>
<seealso><a href="rewritemap.html">RewriteMap</a></seealso>
<seealso><a href="advanced.html">Advanced techniques and tricks</a></seealso>
<seealso><a href="avoid.html">When not to use mod_rewrite</a></seealso>

<section id="per-hostname">

  <title>Virtual Hosts For Arbitrary Hostnames</title>

  <dl>
    <dt>Description:</dt>

    <dd>
    <p>We want to automatically create a virtual host for every hostname
    which resolves in our domain, without having to create
    new VirtualHost sections.</p>

    <p>In this recipe, we assume that we'll be using the hostname
    <code>www.<strong>SITE</strong>.example.com</code> for each
    user, and serve their content out of
    <code>/home/<strong>SITE</strong>/www</code>.</p>
    </dd>

    <dt>Solution:</dt>

    <dd>

<example>
RewriteEngine on<br />
<br />
RewriteMap    lowercase int:tolower<br />
<br />
RewriteCond   %{lowercase:%{<strong>HTTP_HOST</strong>}}   ^www\.<strong>([^.]+)</strong>\.example\.com$<br />
RewriteRule   ^(.*) /home/<strong>%1</strong>/www$1
</example></dd>

<dt>Discussion</dt>
    <dd>

    <note type="warning">You will need to take care of the DNS 
    resolution - Apache does
    not handle name resolution. You'll need either to create CNAME 
    records for each hostname, or a DNS wildcard record. Creating DNS
    records is beyond the scope of this document.</note>

<p>The internal <code>tolower</code> RewriteMap directive is used to
ensure that the hostnames being used are all lowercase, so that there is
no ambiguity in the directory structure which must be created.</p>

<p>Parentheses used in a <directive
module="mod_rewrite">RewriteCond</directive> are captured into the
backreferences <code>%1</code>, <code>%2</code>, etc, while parentheses
used in <directive module="mod_rewrite">RewriteRule</directive> are
captured into the backreferences <code>$1</code>, <code>$2</code>,
etc.</p>

<p>
As with many techniques discussed in this document, mod_rewrite really
isn't the best way to accomplish this task. You should, instead,
consider using <module>mod_vhost_alias</module> instead, as it will much
more gracefully handle anything beyond serving static files, such as any
dynamic content, and Alias resolution. 
</p>
    </dd>
  </dl>

</section>

<section id="simple.rewrite"><title>Dynamic
    Virtual Hosts Using <module>mod_rewrite</module></title>

    <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, 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>Because <code>mod_rewrite</code> runs before other URI translation
    modules (e.g., <code>mod_alias</code>), <code>mod_rewrite</code> must
    be told to explicitly ignore any URLs that would have been handled
    by those modules. And, because these rules would otherwise bypass
    any <code>ScriptAlias</code> directives, we must have
    <code>mod_rewrite</code> explicitly enact those mappings.</p>

<example>
# get the server name from the Host: header<br />
UseCanonicalName Off<br />
<br />
# splittable logs<br />
LogFormat "%{Host}i %h %l %u %t \"%r\" %s %b" vcommon<br />
CustomLog logs/access_log vcommon<br />
<br />
&lt;Directory /www/hosts&gt;<br />
<indent>
    # ExecCGI is needed here because we can't force<br />
    # CGI execution in the way that ScriptAlias does<br />
    Options FollowSymLinks ExecCGI<br />
</indent>
&lt;/Directory&gt;<br />
<br />
RewriteEngine On<br />
<br />
# a ServerName derived from a Host: header may be any case at all<br />
RewriteMap  lowercase  int:tolower<br />
<br />
## deal with normal documents first:<br />
# allow Alias /icons/ to work - repeat for other aliases<br />
RewriteCond  %{REQUEST_URI}  !^/icons/<br />
# allow CGIs to work<br />
RewriteCond  %{REQUEST_URI}  !^/cgi-bin/<br />
# do the magic<br />
RewriteRule  ^/(.*)$  /www/hosts/${lowercase:%{SERVER_NAME}}/docs/$1<br />
<br />
## and now deal with CGIs - we have to force a handler<br />
RewriteCond  %{REQUEST_URI}  ^/cgi-bin/<br />
RewriteRule  ^/(.*)$  /www/hosts/${lowercase:%{SERVER_NAME}}/cgi-bin/$1  [H=cgi-script]<br />
</example>

</section>

<section id="xtra-conf"><title>Using a Separate Virtual Host Configuration File</title>

    <p>This arrangement uses more advanced <module>mod_rewrite</module>
    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 should look something like
    this:</p>

<example>
customer-1.example.com  /www/customers/1<br />
customer-2.example.com  /www/customers/2<br />
# ...<br />
customer-N.example.com  /www/customers/N<br />
</example>

    <p>The <code>httpd.conf</code> should contain the following:</p>

<example>
RewriteEngine on<br />
<br />
RewriteMap   lowercase  int:tolower<br />
<br />
# define the map file<br />
RewriteMap   vhost      txt:/www/conf/vhost.map<br />
<br />
# deal with aliases as above<br />
RewriteCond  %{REQUEST_URI}               !^/icons/<br />
RewriteCond  %{REQUEST_URI}               !^/cgi-bin/<br />
RewriteCond  ${lowercase:%{SERVER_NAME}}  ^(.+)$<br />
# this does the file-based remap<br />
RewriteCond  ${vhost:%1}                  ^(/.*)$<br />
RewriteRule  ^/(.*)$                      %1/docs/$1<br />
<br />
RewriteCond  %{REQUEST_URI}               ^/cgi-bin/<br />
RewriteCond  ${lowercase:%{SERVER_NAME}}  ^(.+)$<br />
RewriteCond  ${vhost:%1}                  ^(/.*)$<br />
RewriteRule  ^/(.*)$                      %1/cgi-bin/$1 [H=cgi-script]
</example>

</section>

</manualpage> 
