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Brandon
Brandon

Reputation: 3146

How do I display output from Python application running inside Docker container?

So, I've got some Python code running inside a Docker container. I started up my local env using Google's gcloud script. I'm seeing basic access style logs and health check info, but I'm not sure how I can pass through log messages I'm writing from my Python app to the console. Is there a parameter I can set to accomplish this with my gcloud script or is there something I can set in the Dockerfile that can help?

Upvotes: 16

Views: 17850

Answers (2)

yuranos
yuranos

Reputation: 9735

(Answer based on the comments)

You don't need to know the container ID if you wrap the app into docker-compose. Just add docker-compose.yml alongside your Dockerfile. It might sound as an extra level of indirection, but for a simple app it's as trivial as this:

version: "3.3"

services:
  build: .
  python_app:
    environment:
      - PYTHONUNBUFFERED=1

That's it. The benefit of having it is that you don't need to pass a lot of flags that docker require because they are added automatically. It also simplifies work with volumes and env vars if they become required later.

You can they view logs by service name:

docker-compose logs python_app

By the way, I'd rather set PYTHONUNBUFFERED=1 if I'm testing something locally. It disabled buffering, which makes logging more deterministic locally. I had a lot of logging problems, for example, when I tried to spin up grpc server in my python app because the logs that are flushed before the server starts were not all init logs I wanted to see. And once the server starts, you will not see the init logs because the logging reattaches to a different/spawned process.

Upvotes: 1

Sentient07
Sentient07

Reputation: 1290

For Python to log on your terminal/command line/console, when executed from a docker container, you should have this variable set in your docker-compose.yml 

  environment:
    - PYTHONUNBUFFERED=0

This is also a valid solution if you're using print to debug.

Upvotes: 28

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