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The Apache HTTP Server Reference Manual
by Apache Software Foundation
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ISBN 9781906966034
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3.78  Apache Module mod_vhost_alias



Description:

Provides for dynamically configured mass virtual hosting

Status:

Extension

Module Identifier:

vhost_alias_module

Source File:

mod_vhost_alias.c



Summary

This module creates dynamically configured virtual hosts, by allowing the IP address and/or the Host: 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.

Note If mod_alias or mod_userdir are used for translating URIs to filenames, they will override the directives of mod_vhost_alias described below. For example, the following configuration will map /cgi-bin/script.pl to /usr/local/apache2/cgi-bin/script.pl in all cases:

ScriptAlias /cgi-bin/ /usr/local/apache2/cgi-bin/
VirtualScriptAlias /never/found/%0/cgi-bin/

Directives:

VirtualDocumentRoot

VirtualDocumentRootIP

VirtualScriptAlias

VirtualScriptAliasIP

See also:

3.78.1  Directory Name Interpolation

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 UseCanonicalName 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 printf which have a number of formats:



%% insert a %
%p insert the port number of the virtual host
%N.M insert (part of) the name


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



0 the whole name
1 the first part
2 the second part
-1 the last part
-2 the penultimate part
2+ the second and all subsequent parts
-2+ the penultimate and all preceding parts
1+ and -1+ the same as 0


If N or M is greater than the number of parts available a single underscore is interpolated.

3.78.2  Examples

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

UseCanonicalName Off
VirtualDocumentRoot /usr/local/apache/vhosts/%0

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

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

UseCanonicalName Off
VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.1/%2.2/%2.3/%2

A request for http://www.domain.example.com/directory/file.html will be satisfied by the file /usr/local/apache/vhosts/example.com/d/o/m/domain/directory/file.html.

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

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

The example request would come from /usr/local/apache/vhosts/example.com/n/i/a/domain/directory/file.html.

Alternatively you might use:

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

The example request would come from /usr/local/apache/vhosts/example.com/d/o/m/ain/directory/file.html.

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

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

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

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

VirtualDocumentRoot /usr/local/apache/vhosts/%2.0.%3.0

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

The LogFormat directives %V and %A are useful in conjunction with this module.

VirtualDocumentRoot Directive

Description:

Dynamically configure the location of the document root for a given virtual host

Syntax:

VirtualDocumentRoot interpolated-directory|none

Default:

VirtualDocumentRoot none

Context:

server config, virtual host

Status:

Extension

Module:

mod_vhost_alias

The VirtualDocumentRoot directive allows you to determine where Apache will find your documents based on the value of the server name. The result of expanding interpolated-directory is used as the root of the document tree in a similar manner to the DocumentRoot directive’s argument. If interpolated-directory is none then VirtualDocumentRoot is turned off. This directive cannot be used in the same context as VirtualDocumentRootIP.

VirtualDocumentRootIP Directive

Description:

Dynamically configure the location of the document root for a given virtual host

Syntax:

VirtualDocumentRootIP interpolated-directory|none

Default:

VirtualDocumentRootIP none

Context:

server config, virtual host

Status:

Extension

Module:

mod_vhost_alias

The VirtualDocumentRootIP directive is like the VirtualDocumentRoot directive, except that it uses the IP address of the server end of the connection for directory interpolation instead of the server name.

VirtualScriptAlias Directive

Description:

Dynamically configure the location of the CGI directory for a given virtual host

Syntax:

VirtualScriptAlias interpolated-directory|none

Default:

VirtualScriptAlias none

Context:

server config, virtual host

Status:

Extension

Module:

mod_vhost_alias

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

VirtualScriptAliasIP Directive

Description:

Dynamically configure the location of the cgi directory for a given virtual host

Syntax:

VirtualScriptAliasIP interpolated-directory|none

Default:

VirtualScriptAliasIP none

Context:

server config, virtual host

Status:

Extension

Module:

mod_vhost_alias

The VirtualScriptAliasIP directive is like the VirtualScriptAlias directive, except that it uses the IP address of the server end of the connection for directory interpolation instead of the server name.

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