High level perspective on the switch from PHP to Python27 Mar 2011
It may be fatuous to write this post before we've actually finished the transition from PHP to Python, but I started writing a different post and this is what came out. Sometimes that happens.
In January of 2010 we started migrating addons.mozilla.org from CakePHP to Django. It was a controversial decision. Developers were ambivalent to excited, managers were opposed to neutral - a split anyone would expect. When I first talked about it I expected to be able to turn off PHP by the end of the year. It didn't turn out quite like that.
Fifteen months later we're still transitioning and it's still stressful. The toughest part about a major migration like this is that there is only one team that is doing the migration, continuing to add the new features we need, and all the while maintaining the old site. That's a stressful environment for developers since the interactions between the languages can be complicated, it's stressful for managers because features take longer to complete, and it's stressful for users (and QA for that matter) because issues will arise which are hard to reproduce and complicated to explain.
In the midst of all the work of migration, the rest of the company is still working: the security team is announcing bounties on our site which means we need to be vigilant about fixing issues, project management continues to come up with features to be added, the site perseveres in its never-ending quest for a new look and feel, and Firefox 4 is using AMO like never before meaning approaching 10,000 hits per second is a regular day. All of that is specific to the add-ons site, but consider your own company if you're thinking of going down the same road - what is coming up for your site that will throw a wrench in the works?
The meat and potatoes of it really comes down to: Given the hindsight of today, would the migration be a good idea? There isn't a right answer for every site, but for AMO we did the right thing1. As of today the majority of pages that matter are on Python - there are some admin tools, and some cron jobs, and the occasional semi-obsolete public page that is on PHP, but for the most part, we're looking really good (less hand waving, more real data). My new (overly optimistic?) plan is to have PHP off by the end of this year. We'll see.
To give you an idea of man-hours, we've had anywhere from 3 to 6 superhero developers working on the site over the past 15 months, and it's looking like the whole thing will take around 24 months. That's a big chunk of time for a site that needs to grow and evolve as quickly as popular sites do these days.
So, overall, I think the lesson is: any reasonably sized site is going to have rabbit holes in it. At first glance AMO might look like it's got a dozen "main" pages, with a couple dozen more supporting pages (and throw in a few more for the admin CRUD). Have a look at that spreadsheet I linked above and you'll see that's not even remotely the case. The spreadsheet even ignores sub-pages in a few places and doesn't include any new features added in the past year. If you're considering a migration, think it through well. Make a spreadsheet of every URL, identify the complicated areas, and make sure everyone is clear on the timeline and what it means for new features. People will absolutely try to scope creep your migration - make it clear if a section of the site is migrating as-is or can be migrated and redesigned at the same time. Redesigns add complexity for the developers but can earn you some good will with the users and managers and if you're in this boat you can use all the good will you can get.
May you have the best of luck with your decisions. :)
1 I'll write another post about pros/cons of the actual frameworks and platforms. Let's just assume we're happy with the technical side of the switch for now.