Comment by bostik

To be fair, I'd consider hard-core scalability/reliability software engineering skills to be their very own speciality domain.

But I'd also claim that these things fall on a spectrum. At the extreme end we have exchanges and HFT-like trading systems, where absolute accuracy and latency are not even constraints but industry fundamentals. At the other end we have "toy" applications that handle tens of requests per second, tops.

Scalability problems are definitely near the extreme end. Only instead of raw latency, you get to deal with complex failure modes, throughput, capacity problems, read amplification and thundering herds... all the while being constrained by available CPU cycles and bounded memory.