CakePHP makes upgrading easy
Laura attended CakeFest a couple months ago and got to meet some core Cake developers in person. In doing so she let slip that AMO was running on a pretty old version (1.1.12 - Released in December of 2006). Apparently 1.1.15 had some major performance boosts and since we melted the cluster a few times recently (the new API was the culprit) we thought it would be a good idea to investigate upgrading.
I downloaded 1.1.15 and 1.1.19, set up a couple symlinks to swap them into my dev copy and looked at how hard it would be to upgrade.
Hats off to the CakePHP developers. After merging in a short patch to the core CakePHP session code, most of the site worked right out of the box. I made a few minor tweaks to our code for things that had changed (and filed ticket 4140 for them) but all in all it was pretty painless. Nice work guys. It shows a lot of planning and foresight to make a framework that doesn't have a bunch of code-breaking changes after years of development.