Missing an order of magnitude? Twitter was claiming to be still running Rails in the mid-2010s, when they apparently had 200+ million active users. The service was finally sunsetted during the big Scala rewrite.

They abandoned their message queue (Starling) written in Ruby early on. That abandonment was often misattributed to them abandoning Rails, I guess because of the shared usage of Ruby. The confusion was compounded to back when someone at Twitter (may have been Odeo at time?) posted a message board rant about how Rails does not scale because ActiveRecord did not allow connecting to multiple databases out of the box. That event seems to be the origins of the "Rails does not scale" mantra that swept the internet for a time. But, humorously, someone replied with a solution a few minutes later.

Ah yes, the Fail Whale era.

They should have kept the fail whale instead of offering "Sorry the tweet couldn't be loaded. Please retry" which I get 3/4 of the time on my phone.

But how many instances did they have running that app, and at what cost? Did they have to build a ridiculous amount of caching in? And wasn't that the time period where they were incredibly unreliable to the point that their "fail whale" server error page became a running gag?

Twitters architecture was a bad joke. Many to many communication in a scalable manner has been a solved problem from decades: you federate. You assign users to buckets, you assign buckets to servers. You route messages like you'd route e-mail. Been there, done that. The federation does not need to be outwardly visible.

Twitters problem was a too centralized architecture not Rails.

And I say that as someone who at the time hated Rails and who still hates Rails. I find it bloated and over-complicated. It may even have led them to make bad architectural choices because of how it was structured.

But they still did make bad architectural choices, and they fixed those choices at the same time they moved off Rails.

Until they had to switch to a mix of Java, Scala and C++.

Had they started with them and there wouldn't exist blue wales.