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I'm trying to containerise a service which listens to a Google PubSub queue of urls, processes the data using some ML models and uploads the results to a firestore DB.

Locally it works as expected, however when it comes to building and running the docker container I see some very strange behaviour. When I run the server through:

CMD ["python3", "urlQueueProcessor.py"]

at the end of the Dockerfile, the script starts but doesn't behave as expected. Some console warnings/startup stuff from packages are printed, but it immediately hangs before reaching any of my code. If I try a print statement before my imports it never shows.

What's stranger is that if I enter the container and run the exact same command through the terminal it does exactly what I expect and starts the server. I made a little script to check the environments and when I run it through CMD and terminal they both show the same output.

Has anyone seen this before? Or is there any workaround that I can try? I've tried starting it through a .sh but it didn't make any difference. I've spent around 2 days on this with no luck so any help would be appreciated. Here's the Dockerfile

Cheers.

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  • can you provide more details? - Dockerfile - how have you connected inside the container? post the exact command Commented Feb 15, 2024 at 17:31
  • I find the container name with docker ps, then use docker exec -it [container_name] /bin/sh (in Windows cmd terminal). I linked the Dockerfile at the end of the post. Commented Feb 15, 2024 at 17:52
  • Does Why doesn't Python app print anything when run in a detached docker container? describe your issue? If not, can you edit the question to include a minimal reproducible example directly in the question and not behind links? Commented Feb 15, 2024 at 18:55
  • @DavidMaze The solutions from that thread actually worked, thank you. I can't believe the server was working all this time but just not able to print the logs. Commented Feb 15, 2024 at 19:46

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The thread that @DavidMaze suggested turned out to be the same issue; the script was running correctly but none of my print statements were being shown in the logs (also making debugging attempts invisible). Specifically, all I needed to do was change:

CMD ["python3", "urlQueueProcessor.py"]

to

CMD ["python3", "-u", "urlQueueProcessor.py"]
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