alt Hacker Newsfrom experience, during bursts it's never actual web/api server that is bogged down, it's the downstream io bottlenecks.
if your accepting layer is abstracted away and implemented correctly, there is very little performance difference between different concurrency approaches and all you're exposed to as developer is implementation of your handler functions.
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(Upvoted for a really relevant and valuable refinement to the thread.)
Admittedly that layer is almost always abstracted i.e. AWS / GCP and various other smaller hosted solutions that handle a good chunk of load balancing for us. In that landscape BEAM VM's strengths shine even brighter. I've seen firsthand that you can in fact bring a BEAM VM to its knees if you expose it just like that to the net. It's not pretty. Golang fares a touch better and Rust seems almost immune (provided one does not screw up their caching layer and don't do elementary N+1 query mistakes).
Not the case; good abstractions are valuable, but the performance differences between runtimes are very real.
Take the example of some simple HTTP<->blob store service gets slammed with millions of requests when someone using the API does a backfill via some framework on their end that aggressively scales request volume up and out.
Something like, say, async Python/starlette with a coroutine per request is gonna perform slightly worse than Erlang, which in turn is gonna perform much worse than Go.
You're right that those differences are sometimes marginal when the latency of whatever IO the backend's doing dominates the equation. However, in my experience huge volume surges show issues with the runtime (the thing managing/launching multiplexed request handler routines) or the ecosystem (the backend IO libraries' ability to work with the runtime's IO multiplexing and make things like request coalescing easy or automatic) more often than you'd think.
It really takes surprisingly little volume to cripple a return-hello-world Phoenix app that indirects the "hello world" behind way too much middleware and message passing; it takes even less to kick over, say, a Gunicorn instance returning "hello world" at the bottom of the Django middleware stack. Golang with Gin, on the other hand, is surprisingly hard to cripple in the same way. And I say that as someone who likes Elixir and Python a lot more than I like Go!