"Our approach to blocking links" https://help.twitter.com/en/safety-and-security/phishing-spa...

"The Infrastructure Behind Twitter: Scale" https://blog.twitter.com/engineering/en_us/topics/infrastruc...

"Mux" https://twitter.github.io/finagle/guide/Protocols.html#mux

I do agree that some of this could be done better a decade later (like, using Rust for some things instead of Scala), but it was all considered. A single machine is a fun thing to think about, but not close to realistic. CPU time was not usually the concern in designing these systems.