[pas]

C10k is the classic problem that made event-driven systems (async programming) the "must have" for modern distributed systems. Especially coupled with websocket proxying. Thousands of long lived connections, but individually they are all very light work, so the cost of switching had started to dominate the work done by the CPU.

Sure, it can be handled as a big array where every element is a struct consisting of the ingress and egress socket/fd referencse, read and write buffers, and some saved state label, and then crunching all of it in a big while loop, in C, with epoll. Nginx does this, but that big array can become the bottleneck quickly. (Lock contention, cache line conflicts resulting in poor memory bandwidth utilization, etc.)

But if you have low-overhead async-await, then you don't have to solve the big array problem and you don't have to write that huge state machine thing either, things become easy[-er] to reason about again.