We are excited to announce that Pantheon now supports choosing your PHP version, allowing you to safely test and upgrade to the latest and greatest version for your site. PHP 5.5 offers a lot of new features for developers, as well as significant increases in performance. In our internal benchmarks, we measured code execution time decrease by over 20% on a Panopoly site, which included over 100 enabled modules:
Pantheon allows you to change your Dev, Test, and Live environments individually per environment, in any combination of Pantheon’s two PHP versions (5.3 & 5.5) as you so desire. Yes, you can choose your own PHP adventure!
To upgrade safely, first change the Development environment version to PHP 5.5 to test it out. If you see no errors on the site or in your logs, you're good to go. If you want to be extra cautious, you can toggle Testing and do a final run through there as well, and then come back to the menu and change the default for all of your environments to 5.5.
However, if you do see issues in Development, you need to make a decision: will you dig in and fix them now, or roll back to PHP 5.3? It's important to make a strong choice at that time, as leaving your environments in an inconsistant state will be a major "gotcha" later on down the line.
Unless your primary development focus is completing a version upgrade, you should roll back until you're ready to take that on as the singular focus of your work. Do, or do not; there is no try. Any other course of action will complicate your work as you'll be left guessing whether or not things will be consistent as you deploy — not a situation a developer wants to see.
PHP toggling is available in each site’s dashboard at the settings menu. Simple, clean and easy to use...PHP versioning is here!
For detailed instructions, see Toggling Between PHP Versions.: Development