There are several reasons you might need to run multiple versions of PHP on the same server. Maybe you have a PHP 5.2 application running on your server and you need to start working on another application based on a new framework like Symfony2 or Lithium? Perhaps you haver a client with a legacy site that runs PHP 5.2, or maybe you simply want to test some of the new functionality? This post is going to explain how to setup a server to run multiple versions of PHP.

Normally, Apache can only be compiled with one version of PHP, but FastCGI gets around that by letting you define it in a configuration file instead. They also include support for defining the user the process runs as (suexec) that helps to make permissions issues lesser. Included are all of the command-line calls and config settings you'll need to make to get things set up.

The challenge with securing a shared hosting server is how to secure the website from attack both from the outside and from the inside. PHP has built-in features to help, but ultimately it's the wrong place to address the problem.

His guide steps through the entire process - getting the software, configuring Apache (with the PHP/CGI installation) and configuring suexec, both for the default install and then for the shared server settings. There's even a few brief benchmarks showing the speed of execution for scripts with and without the suexec environment.