mod_macro

Apache Module mod_macro

Summary

Provides macros within Apache httpd runtime configuration files, to ease the process of creating numerous similar configuration blocks. When the server starts up, the macros are expanded using the provided parameters, and the result is processed as along with the rest of the configuration file.

Usage

Macros are defined using <Macro> blocks, which contain the portion of your configuration that needs to be repeated, complete with variables for those parts that will need to be substituted.

For example, you might use a macro to define a <VirtualHost> block, in order to define multiple similar virtual hosts:

<Macro VHost $name $domain>
<VirtualHost *:80>
    ServerName $domain
    ServerAlias www.$domain

    DocumentRoot "/var/www/vhosts/$name"
    ErrorLog "/var/log/httpd/$name.error_log"
    CustomLog "/var/log/httpd/$name.access_log" combined
</VirtualHost>
</Macro>

Macro names are case-insensitive, like httpd configuration directives. However, variable names are case sensitive.

You would then invoke this macro several times to create virtual hosts:

Use VHost example example.com
Use VHost myhost hostname.org
Use VHost apache apache.org

UndefMacro VHost

At server startup time, each of these Use invocations would be expanded into a full virtualhost, as described by the <Macro> definition.

The UndefMacro directive is used so that later macros using the same variable names don't result in conflicting definitions.

A more elaborate version of this example may be seen below in the Examples section.

Tips

Parameter names should begin with a sigil such as $, %, or @, so that they are clearly identifiable, and also in order to help deal with interactions with other directives, such as the core Define directive. Failure to do so will result in a warning. Nevertheless, you are encouraged to have a good knowledge of your entire server configuration in order to avoid reusing the same variables in different scopes, which can cause confusion.

Parameters prefixed with either $ or % are not escaped. Parameters prefixes with @ are escaped in quotes.

Avoid using a parameter which contains another parameter as a prefix, (For example, $win and $winter) as this may cause confusion at expression evaluation time. In the event of such confusion, the longest possible parameter name is used.

If you want to use a value within another string, it is useful to surround the parameter in braces, to avoid confusion:

<Macro DocRoot ${docroot}>
    DocumentRoot "/var/www/${docroot}/htdocs"
</Macro>

Examples

Virtual Host Definition

A common usage of mod_macro is for the creation of dynamically-generated virtual hosts.

## Define a VHost Macro for repetitive configurations

<Macro VHost $host $port $dir>
  Listen $port
  <VirtualHost *:$port>

    ServerName $host
    DocumentRoot "$dir"

    # Public document root
    <Directory "$dir">
        Require all granted
    </Directory>

    # limit access to intranet subdir.
    <Directory "$dir/intranet">
      Require ip 10.0.0.0/8
    </Directory>
  </VirtualHost>
</Macro>

## Use of VHost with different arguments.

Use VHost www.apache.org 80 /vhosts/apache/htdocs
Use VHost example.org 8080 /vhosts/example/htdocs
Use VHost www.example.fr 1234 /vhosts/example.fr/htdocs

Removal of a macro definition

It's recommended that you undefine a macro once you've used it. This avoids confusion in a complex configuration file where there may be conflicts in variable names.

<Macro DirGroup $dir $group>
  <Directory "$dir">
    Require group $group
  </Directory>
</Macro>

Use DirGroup /www/apache/private private
Use DirGroup /www/apache/server  admin

UndefMacro DirGroup

<Macro name [par1 .. parN]> ... </Macro>

<Macro LocalAccessPolicy>
    Require ip 10.2.16.0/24
</Macro>

<Macro RestrictedAccessPolicy $ipnumbers>
    Require ip $ipnumbers
</Macro>

UndefMacro name

UndefMacro LocalAccessPolicy
UndefMacro RestrictedAccessPolicy

Use name [value1 ... valueN]

Use LocalAccessPolicy
...
Use RestrictedAccessPolicy "192.54.172.0/24 192.54.148.0/24"

Require ip 10.2.16.0/24
...
Require ip 192.54.172.0/24 192.54.148.0/24