`CancelledError` raised on app startup in Argo CD

[ishaan-mehta]

I have a FastAPI app that uses uvicorn, and when I run locally with Docker on colima, I never encounter this error, but when I run that same app in Argo CD, I keep seeing the following error and the app immediately shuts down:

INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
ERROR:    Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/starlette/routing.py", line 700, in lifespan
    await receive()
  File "/usr/local/lib/python3.12/site-packages/uvicorn/lifespan/on.py", line 137, in receive
    return await self.receive_queue.get()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/asyncio/queues.py", line 158, in get
    await getter
asyncio.exceptions.CancelledError

(This is transient, however — very rarely, the app does manage to get past this and start without issue.)

As far as I can tell, this error is never supposed to actually surface to the user. How can I solve this? Is this an issue with uvicorn? An issue with starlette? (I am not using Ctrl-C or interacting with the app at all, which I have seen suggested on similar discussions online.)

Originally posted by @ishaan-mehta in #2495

[tonnico]

I see a similar problem in my setup.

Maybe it is an issue with the latest websockets major release?
On my test setup a downgrade to websockets==13.1 will fix the issue.

[hunter2009pf]

same problem, how to fix it?

[Kludex]

Please create a discussion with an MRE.