Getting CancelledError Python FastAPI application using openai chat completion

[stone hinge]

I have Python FastAPI application that uses openai's chat completion api with stream. I am getting CancelledError very frequently. I also added timeout middleware with 2 mins timeout and is still same error.

The same prompts works fine on my local machine. It's happening only in Railway. I guess may have to tweak some timeout out setting in Railway. I will provide full stack trace below. Please let me know how to resolve it.

CancelledError('Cancelled by cancel scope 7fa0af45f910')Traceback (most recent call last):\n\n\n File \"/usr/local/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py\", line 472, in astream\n async for chunk in self._astream(\n\n\n File \"/usr/local/lib/python3.10/site-packages/langchain_openai/chat_models/base.py\", line 1989, in astream\n async for chunk in super().astream(*args, **kwargs):\n\n\n File \"/usr/local/lib/python3.10/site-packages/langchain_openai/chat_models/base.py\", line 779, in astream\n async for chunk in response:\n\n\n File \"/usr/local/lib/python3.10/site-packages/openai/streaming.py\", line 147, in aiter\n async for item in self._iterator:\n\n\n File \"/usr/local/lib/python3.10/site-packages/openai/_streaming.py\", line 160, in stream\n async for sse in iterator:\n\n\n File \"/usr/local/lib/python3.10/site-packages/openai/_streaming.py\", line 151, in iterevents\n async for sse in self._decoder.aiter_bytes(self.response.aiter_bytes()):\n\n\n File \"/usr/local/lib/python3.10/site-packages/openai/_streaming.py

[sterile geyser]

Project ID: ab55d7b2-61b7-4e97-b893-4b10bd69492b

[stone hinge]

ab55d7b2-61b7-4e97-b893-4b10bd69492b

[peak tundra]

for clarity, this is not an issue with railway, you would not have to tweak settings in railway, this is an application level issue.

how long are these streams?

[stone hinge]

@peak tundra I don't have this issue when running locally.

I also tried increasing async time out using middle ware and no luck.

The response streams only for few seconds

[peak tundra]

it's good start that it works locally but please keep in mind that it does not mean you don't have an application level issue.

since this is an application level issue we would need a minimal reproducible example.

[stone hinge]

Thank you @peak tundra .

I tried lot of troubleshooting options today like changing from guvicorn to uvicorn , setting keep-alive timeout in uvicorn and refactoring code to handle timeout etc. But none of it worked.

Then, I installed docker and ran my app inside docker and it works perfectly fine.

I will attach debug logs from local and inside railway app to see if that helps.

I have spent whole day today trying to debug this and no luck. Any help will be greatly appreciated.

[peak tundra]

since this is an application level issue we would need a minimal reproducible example.

[stone hinge]

Thank you @peak tundra Here is minimal example to reproduce.

App url : https://streamingfastapiexample-production.up.railway.app/ - when you click streaming response will stream, but it will stop before finishing.
Code : https://github.com/erajasekar/StreamingFastAPIExample ( Use master branch)

FYI - I deployed same exact code on another clould provider render and it works fine https://streamingfastapiexample.onrender.com/.

I am guess that there is some http connection or timeout parameter we need to tweak on Railway.

[peak tundra]

just for the record other cloud providers tend to monkey patch away a lot of user mistakes, but Railway will over ever run your code as-is

this is SSE, please see this proof of concept that has no such issues - https://utilities.up.railway.app/sse

ive had it run for multiple minutes without stopping, this further cements the fact that this is an application level issue.

[stone hinge]

hmm. Thank you for example. But it's sending events after every second. what happens when delay between events is more than 1 second and random. The example I provided has minimal code of my application and it is using openai's streaming sdk.

If you show if my minimal example working or help me troubleshoot, I would really appreciate.

Thank you for your support on weekend.

[peak tundra]

ill try to implement a similar endpoint in my example app

done, though it just streams the embedded text, it doesnt use openai - https://utilities.up.railway.app/sse2

[stone hinge]

Thanks, It's very tricky problem. I tried lot of things on application level, but nothing worked.

[peak tundra]

this is clearly an application level issue, i suggest getting even more minimal

[stone hinge]

This is a minimum MVP example to confirm that I could deploy my app in Railway.

[peak tundra]

it can get even more minimal, remove openai

[stone hinge]

I have to use open api for my product. I doubt it's issue in openapi python library as it is used in chatgpt and many other applications.

[peak tundra]

right but you need to eliminate all variables

[stone hinge]

Hi @peak tundra , Is there any proxy used for outbound communication from Railway servers to external apis ?

I use a python library for extracting youtube transcripts which works fine in Railway, but it doesn't work in render.

When I researched further I found that youtube blocks requests from cloud machine servers and possible solution to get around is to use a proxy.

But youtube is not blocking requests from Railway

[peak tundra]

we do not have any proxy / filtering / firewall on outbound traffic

[stone hinge]

Ok, it appears that there is some issue related to outbound communication from Railway to OpenAI related to streaming.

[peak tundra]

nope, this would be an application level issue, it is not productive for you to pin this issue on the platform

[stone hinge]

This is based on what I find from troubleshooting. My goal to not to pin point problem with the platform and but to figure out a solution for my issue.

Let me know if this is something that could be resolved through support or I should move to another platform instead of spending time in trouble shooting this.

Thank you for being with me in debugging this.

[peak tundra]

unfortunately we can not provide application level support, so theres not much more we can do here as this is not an issue with the platform

[peak tundra]

switched my own program over to using the same exact same openai completion, same prompt, same model, same settings, same everything, but written in golang.

i can reproduce this locally, meaning this is very much not an issue with railway.

[STREAM_CLOSED] means openai closed the stream.

found your issue.

you set max_tokens to 512 - https://github.com/erajasekar/StreamingFastAPIExample/blob/master/fastapp.py#L21

and so did i in my 1:1 golang rewrite.

the response i showed above reached 512 tokens exactly

@stone hinge for viz

[stone hinge]

Thank you @peak tundra . The example application works after increasing token count. But my actual application still fails. will troubleshoot.

[peak tundra]

during however many dozens of times I've used your Railway hosted site, it never outright failed to stream me text, what issue are you getting?

[stone hinge]

async CancelledError.

Attaching the logs and source code of original application that is failing.

( minimal example version works fine after increasing token size, it's still not clear how it works on local with 512 token size and not from Railway ).

[peak tundra]

that just looks like you not handling an error properly

[stone hinge]

Added logging for exception handling gives me this stack trace:

asyncio.exceptions.CancelledError: Cancelled by cancel scope 7fa2af3bd900

 

During handling of the above exception, another exception occurred:

 

Traceback (most recent call last):

  File "/app/api/v1/chat.py", line 60, in streaming_response

    async for chunk in llm_service.continue_chat(user_id, session_id, chat_request.message):

  File "/app/services/llm_service.py", line 128, in continue_chat

    async for chunk in self.systhesis_video_transcript_stream(user_id, session['transcript']):

  File "/app/services/llm_service.py", line 88, in systhesis_video_transcript_stream

    async for chunk in chain.astream(input="Synthesize the video transcript."):

  File "/usr/local/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 3430, in astream

    async for chunk in self.atransform(input_aiter(), config, **kwargs):

  File "/usr/local/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 3413, in atransform

    async for chunk in self._atransform_stream_with_config(

  File "/usr/local/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 2332, in _atransform_stream_with_config

    await run_manager.on_chain_error(e, inputs=final_input)

asyncio.exceptions.CancelledError: Cancelled by cancel scope 7fa2af3bd900

Not sure what is causing this

[peak tundra]

you are now using langchan? i thought you where using openai

either way, we can't help here since this is coding issue and we dont offer coding help