Because we're in full throes of Zend Framework 2.0 development, I find myself with a variety of PHP binaries floating around my system from both the PHP 5.2 and 5.3 release series. We're at a point now where I'm wanting to test migrating applications from ZF 1.X to 2.0 to se see what works and what doesn't. But that means I need more than one PHP binary enabled on my server...
I use Zend Server on my development box; it's easy to install, and uses my native Ubuntu update manager to get updates. On Ubuntu, it installs the Debian Apache2 packages, so I get the added bonus of familiarity with the configuration structure.
I installed Zend Server some time ago, so I'm still on a PHP 5.2 mod_php binary. I have several PHP 5.3 binaries compiled and installed locally for running unit tests and sample scripts already -- so the question was how to keep my 5.2 mod_php running while simultaneously allowing the ability to run selected vhosts in 5.3?
The answer can be summed up in one acronym: FastCGI.