Here we go, someone's throwing around the S word again. Based on my experience, every time someone mentions "scalability" in a web application context I smell red flags.

Now we don't have details on what the comments service in Reddit entails - maybe it does indeed do a lot of CPU-intensive processing, in which case moving to Golang will definitely help.

But maybe it's also just a trivial "read from DB, spit out JSON", in which case the bottleneck will always be the DB, and "scalability" is just an excuse to justify the work.

The fact this is part of a move off a "legacy" system to "modern" "microservices" suggests there's a huge amount of developers having fun and are incentivized to justify continuing getting paid to have fun replacing a perfectly functioning system, rather than an actual hard blocker to scalability that can't be solved in a simpler way like by throwing more hardware at it.