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Comment by marknutter | Hacker News Reader

I thought Twitter was always the canonical example for a large Ruby on Rails app. Although these days it's splintered into a very large variety of different technologies, I believe Rails is still in the mix somewhere.

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Nope, their entire stack is JVM based now.

That wouldn't exclude JRuby though

I know they're not using JRuby

That's not the move they made; they moved to Scala. Their original Rails app couldn't scale. They now use Rails on the front end, but the real data isn't Rails. This has been written about extensively:

http://highscalability.com/blog/2013/7/8/the-architecture-tw...

http://highscalability.com/scaling-twitter-making-twitter-10...

The newer link doesn't mention them using Rails anymore. It's probably still in use in some internal apps, but the main twitter.com site should be 100% Scala now.

No, I asked to an engineer last month and their still using their 'Monorail' for twitter.com

Not entire stack, they are still using some parts of the original monorail app in their stack.

This was true as of July 2013. Source: A Twitter Engineer working on the Tweets Service inside their mothership SoA Application.

I spoke to an engineering manager at Twitter a few months ago. While he did not definitively say that "all" front-facing code is in Scala, when I asked him where does Twitter still use Ruby on Rails, he said something along the lines of "We still use Ruby on Rails for internal tools," which would imply that the main Twitter app is mostly/all Scala.

Would the backend operations be part of that? Stuff like indexing, caching, database maintenance, etc

I can reasonably assume that those tasks are not what he meant by "internal tools." When someone talks about "internal tools," they are referring to stuff like internal dashboards. Other hypothetical examples: 1) internal bug tracker, 2) a custom CRM for a company's sales team, 3) an internal message board, 4) a conference room scheduler, 5) a dashboard to view the health of a service, etc etc.

I believe the front-facing Twitter.com is all Scala, but a lot of their internal and smaller sites are RoR.

Thought it was the other way around: RoR still exists in the UI but they transitioned to Scala due to all the outages they had 3-5 years ago.

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