IIS completly hang (Full Request Pipeline)

Short story about a developer issue :)

Imagine:

You have a frontend, which starts an import process.

After starting the import process, the frontend continuously asks for the status. Nothing new here, so far.

I tried to debug the backend, while the frontend continuously calls my backend.

This caused, that the backend in most cases was completely unresponsive and all services on this AppPool were unresponsive.

The mistake was, that the frontend was calling the backend in loop. Without waiting for the results, before doing the next call (because logic was in .then()).

This caused that the request pipeline of IIS was full and IIS stopped everything and I got TaskCancelledExceptions in my backend. Those Exceptions occured in my HttpClient on backend, which calls a different service (microservice architecture). This issue was very hard to solve, because you don't know what happens on backend. You just get these exceptions and wonder why they timeout in such a short time.

Lesson learned: Never loop in frontend, without waiting for the result!

This issue only appeared in debugger.