May I introduce you to erlang/BEAM? These issues were solved 30 years ago, and the ecosystem has had plenty of time to solidify best practices around exactly what you're asking for.

What actually BEAM protect you against resources consumption ? If you set o timeout all you process will be up and idle.

Default BEAM timeout is usually 5s (probably too long, in some cases), if you miss it the default is unhandled exception, which crashes the process that made the call (and only that process, no others). The VM will then recover all of the resources (file descriptors, sockets, data to be GC'd) associated with that process. All in zero lines of code.

Also you can have millions of processes per core, with minimal performance regression, do you're likely to notice it in monitoring before it becomes a problem.

hmm -- this is a compelling sales pitch. What should I read to learn about how erlang API clients manage pooling + timeout logic?

To be honest I use elixir. Docs are better anyways. For timeouts that information is in the standard library, for example

https ://hexdocs.pm/elixir/GenServer.html#call/3

Note that call is even more sophisticated, it incorporates a liveness check on its counterparty to quit out before timeout if there's been a catastrophe. Note this is effectively a simple form of backpressure management that degrades availability gracefully under stress in favor of ensuring the integrity of existing connections. Because fallibility is so baked into the runtime, every good library incorporates timeouts where it's sensible.

For connection pools, it's not explicitly part of the standard library but basically everyone (maybe not whatsapp) uses poolboy:

https://elixirschool.com/en/lessons/libraries/poolboy/

I have never used it myself, yet, but I trust more experienced devs have incorporated it successfully in ecto (rdbms) and Phoenix (web framework).