Twitter's frontend is still definitely Ruby (on Rails). Based on what I've heard from people who have consulted there, it's a gigantic ball of crap. They've so heavily patched Rails 2.0 that they can't realistically migrate to a more modern version of Rails.

Which is sorta ridiculous considering that it's definitely not among the most complex of the Web apps out there. Even late competitors like www.shoutem.com are much more complex as they allow for a bunch of Twitters to be created on the same platform.

The only complex thing about Twitter is its size, and I bet their developers are working round the clock just to keep it from falling apart.

I do a fair amount of Rails, so I'm really curious here. How could it be that they've so heavily patched 2.0 that they can't move on? Anyone from Twitter care to comment?

I've worked on many Rails apps, and have upgraded the apps from version to version. It's a pain when key elements of the API shift, but it's not that bad...even when the project has monkey-patched Rails a lot. And twitter certainly has the resources to afford to dedicate a few programmers to this task, so I'm just not sure I buy it.

One of the contractors I spoke with said that they had a branch running Rails 2.1 successfully. When they deployed it in production, the entire application fell on its face.

Supposedly, the problem was caused by Cache Money, but nobody at Twitter wanted to risk moving to a different version again. They're still on 2.0 today. :-)

Another fun fact: Twitter has over 1,500 remote git branches. They also have bright green deer in the reception area of their office. :-)

FB is on a much different scale so it'll be out of question for short term but I wonder if they have looked at Quercus.