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<modulesynopsis>

<name>mod_vhost_alias</name>
<description>Provides for dynamically configured mass virtual
hosting</description>
<status>Extension</status>
<sourcefile>mod_vhost_alias.c</sourcefile>
<identifier>vhost_alias_module</identifier>

<summary>

    <p>This module creates dynamically configured virtual hosts, by
    allowing the IP address and/or the <code>Host:</code> header of
    the HTTP request to be used as part of the pathname to
    determine what files to serve. This allows for easy use of a
    huge number of virtual hosts with similar configurations.</p>


</summary>
    <seealso><directive
    module="core">UseCanonicalName</directive>.</seealso>
    <seealso><a href="../vhosts/mass.html">Dynamically configured mass 
virtual hosting</a></seealso>

<section>
    <title>Directory Name Interpolation</title>

    <p>All the directives in this module interpolate a string into
    a pathname. The interpolated string (henceforth called the
    "name") may be either the server name (see the <a
    href="core.html#usecanonicalname"><code>UseCanonicalName</code></a>
    directive for details on how this is determined) or the IP
    address of the virtual host on the server in dotted-quad
    format. The interpolation is controlled by specifiers inspired
    by <code>printf</code> which have a number of formats:</p>

<table>

<tr><td><code>%%</code></td>
<td>insert a <code>%</code></td></tr>

<tr><td><code>%p</code></td>
<td>insert the port number of the virtual host</td></tr>

<tr><td><code>%N.M</code></td>
<td>insert (part of) the name</td></tr>
     
</table>

    <p><code>N</code> and <code>M</code> are used to specify
    substrings of the name. <code>N</code> selects from the
    dot-separated components of the name, and <code>M</code>
    selects characters within whatever <code>N</code> has selected.
    <code>M</code> is optional and defaults to zero if it isn't
    present; the dot must be present if and only if <code>M</code>
    is present. The interpretation is as follows:</p>

    <table>
      <tr><td><code>0</code></td>
      <td>the whole name</td></tr>

      <tr><td><code>1</code></td>
      <td>the first part</td></tr>

      <tr><td><code>2</code></td>
      <td>the second part</td></tr>

      <tr><td><code>-1</code></td>
      <td>the last part</td></tr>

      <tr><td><code>-2</code></td>
      <td>the penultimate part</td></tr>

      <tr><td><code>2+</code></td>
      <td>the second and all subsequent parts</td></tr>

      <tr><td><code>-2+</code></td>
      <td>the penultimate and all preceding parts</td></tr>

      <tr><td><code>1+</code> and <code>-1+</code></td>
      <td>the same as <code>0</code></td></tr>
    </table>

    <p>If <code>N</code> or <code>M</code> is greater than the number
    of parts available a single underscore is interpolated. </p>

</section>

<section>
    <title>Examples</title>

    <p>For simple name-based virtual hosts you might use the
    following directives in your server configuration file:</p>

<example>
    UseCanonicalName    Off<br />
    VirtualDocumentRoot /usr/local/apache/vhosts/%0
</example>

    <p>A request for
    <code>http://www.example.com/directory/file.html</code> will be
    satisfied by the file
    <code>/usr/local/apache/vhosts/www.example.com/directory/file.html</code>.
    </p> 

    <p>For a very large number of virtual hosts it is a good idea
    to arrange the files to reduce the size of the
    <code>vhosts</code> directory. To do this you might use the
    following in your configuration file:</p>

<example>
    UseCanonicalName    Off<br />
    VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.1/%2.2/%2.3/%2
</example>

    <p>A request for
    <code>http://www.example.isp.com/directory/file.html</code>
    will be satisfied by the file
    <code>/usr/local/apache/vhosts/isp.com/e/x/a/example/directory/file.html</code>.</p>

    <p>A more even spread of files can be achieved by hashing from the
    end of the name, for example: </p>

<example>
    VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.-1/%2.-2/%2.-3/%2
</example>

    <p>The example request would come from
    <code>/usr/local/apache/vhosts/isp.com/e/l/p/example/directory/file.html</code>.</p>

    <p>Alternatively you might use: </p>

<example>
    VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.1/%2.2/%2.3/%2.4+
</example>

    <p>The example request would come from
    <code>/usr/local/apache/vhosts/isp.com/e/x/a/mple/directory/file.html</code>.</p>

    <p>For IP-based virtual hosting you might use the following in
    your configuration file:</p>

<example>
    UseCanonicalName DNS<br />
    VirtualDocumentRootIP   /usr/local/apache/vhosts/%1/%2/%3/%4/docs<br />
    VirtualScriptAliasIP    /usr/local/apache/vhosts/%1/%2/%3/%4/cgi-bin
</example>

    <p>A request for
    <code>http://www.example.isp.com/directory/file.html</code>
    would be satisfied by the file
    <code>/usr/local/apache/vhosts/10/20/30/40/docs/directory/file.html</code>
    if the IP address of <code>www.example.com</code> were
    10.20.30.40. A request for
    <code>http://www.example.isp.com/cgi-bin/script.pl</code> would
    be satisfied by executing the program
    <code>/usr/local/apache/vhosts/10/20/30/40/cgi-bin/script.pl</code>.</p>

    <p>If you want to include the <code>.</code> character in a
    <code>VirtualDocumentRoot</code> directive, but it clashes with
    a <code>%</code> directive, you can work around the problem in
    the following way:</p>

<example>
    VirtualDocumentRoot /usr/local/apache/vhosts/%2.0.%3.0
</example>

    <p>A request for
    <code>http://www.example.isp.com/directory/file.html</code>
    will be satisfied by the file
    <code>/usr/local/apache/vhosts/example.isp/directory/file.html</code>.</p>
     
    <p>The <directive module="mod_log_config">LogFormat</directive>
    directives <code>%V</code> and <code>%A</code> are useful
    in conjunction with this module.</p>
</section>

<directivesynopsis>
<name>VirtualDocumentRoot</name>
<description>Dynamically configure the location of the document root
for a given virtual host</description>
<syntax>VirtualDocumentRoot <em>interpolated-directory</em></syntax>
<default>none</default>
<contextlist>
<context>server config</context>
<context>virtual host</context>
</contextlist>

<usage>

    <p>The <code>VirtualDocumentRoot</code> directive allows you to
    determine where Apache will find your documents based on the
    value of the server name. The result of expanding
    <em>interpolated-directory</em> is used as the root of the
    document tree in a similar manner to the <directive
    module="core">DocumentRoot</directive> directive's argument. 
    If <em>interpolated-directory</em> is <code>none</code> then
    <code>VirtaulDocumentRoot</code> is turned off. This directive 
    cannot be used in the same context as
    <directive>VirtualDocumentRootIP</directive>.</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>VirtualDocumentRootIP</name>
<description>Dynamically configure the location of the document root
for a given virtual host</description>
<syntax>VirtualDocumentRootIP <em>interpolated-directory</em></syntax>
<default>none</default>
<contextlist>
<context>server config</context>
<context>virtual host</context>
</contextlist>

<usage>

<p>The <code>VirtualDocumentRootIP</code> directive is like the
    <directive>VirtualDocumentRoot</directive>
    directive, except that it uses the IP address of the server end
    of the connection instead of the server name.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>VirtualScriptAlias</name>
<description>Dynamically configure the location of the CGI directory for
a given virtual host</description>
<syntax>VirtualScriptAlias <em>interpolated-directory</em></syntax>
<default>none</default>
<contextlist>
<context>server config</context>
<context>virtual host</context>
</contextlist>

<usage>

    <p>The <code>VirtualScriptAlias</code> directive allows you to
    determine where Apache will find CGI scripts in a similar
    manner to <directive>VirtualDocumentRoot</directive>
    does for other documents. It matches requests for URIs starting
    <code>/cgi-bin/</code>, much like <directive
    module="mod_alias">ScriptAlias</directive>
    <code>/cgi-bin/</code> would.</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>VirtualScriptAliasIP</name>
<description>Dynamically configure the location of the cgi directory for
a given virtual host</description>
<syntax>VirtualScriptAliasIP <em>interpolated-directory</em></syntax>
<default>none</default>
<contextlist>
<context>server config</context>
<context>virtual host</context>
</contextlist>

<usage>

    <p>The <code>VirtualScriptAliasIP</code> directive is like the
    <a
    href="#virtualscriptalias"><code>VirtualScriptAlias</code></a>
    directive, except that it uses the IP address of the server end
    of the connection instead of the server name.</p>

    </usage>

</directivesynopsis>
</modulesynopsis>

