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Aegir provides some hook functions in its API, one of which allows you to inject extra configuration snippets into your Apache vhost files for sites.

When would I want to do this?

A good example for this is when you may need to inject a custom Rewrite rule that goes beyond what the Aegir Aliases 'redirection' feature provides.

Or, perhaps you have to inject some htpasswd mod_auth password protection for your site, or perhaps a CustomLog definition.

Typically you'd just add what you need to the vhost file, but the problem is that Aegir manages these vhosts, and on every Verify task, will rewrite the config from a template, blowing away your changes in the process. Ouch!

Fortunately there is a very easy and elegant solution to this problem to save your configurations persistently across Verify tasks and the like, by means of invoking the Provision hook provision_apache_vhost_config()

A simple example

In this example I'll inject a simple 'ErrorLog' apache definition into a vhost to save the site error logs to a file.

1. Create a file in ~aegir/.drush called mig5.drush.inc
2. Add this snippet of PHP to the file:
   
<?php
  function mig5_provision_apache_vhost_config($uri, $data) {
    return "ErrorLog /var/aegir/" . $uri . ".error.log";
  }
3. Install a site or verify an existing one

Check your site's vhost config file (in /var/aegir/config/server_master/apache/vhost.d/) and you'll see the line has been injected into the '#Extra configuration' area of the vhost

It's that simple! You can see that via the hook, we pass $uri and the drush data to the function, allowing me to abstract the site url so that each site will get its own error log. You could do extra PHP conditionals to ensure certain data only gets inserted into certain sites of a specific name.

To inject multiple lines instead of one, use an array, i.e

The key point of this is that the file ~aegir/.drush/mig5.drush.inc file will never be touched by Aegir, so you can rest assured your changes will be respected.