Do they even use Scala? I thought they were using Java (but I may have outdated knowledge). Lichess is written in Scala. Do you have any pointer to an article describing chess.com tech stack?
It was a pithy comment on Lichess's recent post on upgrading to Scala 3.
The listings on https://www.chess.com/jobs provide some hints. Some mentions of PHP and Java for the backend, Kubernetes, Kafka, Redis, MySQL, Mongo, AWS, and GCP, among other things.
Did someone say resume driven development?
So, Web-scale tech? </snark> I bet load is more on the everything but the chess engine itself.
Well there’s the bottleneck in a nut shell. Ditch the PHP. At least consider Play if you can’t ditch the Java (I can’t vouch for it, but theoretically it should help.)
Otherwise they should consider Elixir/Phoenix as it is easily distributable and/or Rust if they need breakneck speed per thread.