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docker-compose -e flag does not override default value

I have created the following docker-compose.yml:

version: "3.8"

services:
  app:
    image: my-image
    build:
      context: .
      dockerfile: Dockerfile
    working_dir: /src
    command: python ${SCRIPT}
    environment:
      - .env

  app-dev:
    extends:
      service: app
    volumes:
      - ./src:/src

My .env file has one line:

SCRIPT=./tutorial_00/docker_test.py

I will now do the following steps:

  1. Build the docker image: docker-compose up --build app
    This will build the image and run the docker_test.py script
  2. Now I want to run a different python script using this command: docker-compose run --rm -e SCRIPT=tutorial_01/main.py app
    This should override the default value for the SCRIPT variable which was retrieved from the .env file with tutorial_01/main.py. However it ignores this flag and still runs the default script. I don’t really know why. It seems like the parameter is completely ignored.

If I run the following command docker-compose run --rm -e SCRIPT=./tutorial_01/main.py app env it shows me that the variable was set successfully:

PATH=/venv/bin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=e420aa256ae69
TERM=xterm
SCRIPT=./tutorial_01/main.py
LANG=C.UTF-8
GPG_KEY=A035C8C19219BA821E8D684696D
PYTHON_VERSION=3.11.9
PYTHON_PIP_VERSION=24.0
PYTHON_SETUPTOOLS_VERSION=65.5.1

If I set ./tutorial_01/main.py as the default value in .env it successfully runs this file instead. So the path is definetly valid.

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2

Answers


  1. Chosen as BEST ANSWER
    0

    EDIT: A real answer was given and marked as such. I'm just leaving this here fyi. However I'd not recommend doing it this way. Use the solution provided by "Hans Kilian" instead.

    I experimented a little bit and I'm starting to think that variables inside the command: block are not possible. I assume the command you are actually running has to be static. Therefore I am using the following workaround. I run a static file which will run the correct file for me based on the given environment variable. I updated the docker-compose.yml as follows:

    version: "3.8"

services:
  app:
    image: my-image
    build:
      context: .
      dockerfile: Dockerfile
    working_dir: /src
    command: python start.py
    environment:
      - SCRIPT=./tutorial_00/docker_test.py

  app-dev:
    extends:
      service: app
    volumes:
      - ./src:/src

    Then I created a new python file called start.py inside my docker src directory which will get the ENV SCRIPT and runs a python file at that location:

    import os
import subprocess
import sys


def main():
    # Retrieve the environment variable 'SCRIPT'
    script_path = os.getenv('SCRIPT')

    if not script_path:
        print("Error: The 'SCRIPT' environment variable is not set.")
        sys.exit(1)

    # Check if the file exists
    if not os.path.isfile(script_path):
        print(f"Error: The file at '{script_path}' does not exist.")
        sys.exit(1)

    # Execute the Python script
    try:
        subprocess.run([sys.executable, script_path], check=True)
    except subprocess.CalledProcessError as e:
        print(
            f"Error: The script at '{script_path}' failed with exit code {e.returncode}.")
        sys.exit(e.returncode)


if __name__ == "__main__":
    main()

    Now I can successfully run any python script by passing the SCRIPT variable during the docker-compose run command:

    docker-compose run --rm -e SCRIPT=tutorial_02/main.py app

    This definitely works but it feels like a bit of a "shady" workaround. Let me know if there is a better way to do this.


  2. 0

    When talking about compose and environment variables, you have to be careful about if the variables are for compose or for the container.

    The -e option with docker compose run is for the container. So when you run

    docker-compose run --rm -e SCRIPT=./tutorial_01/main.py app env

    the SCRIPT variable is set inside the container and is not available in the compose file.

    To make a variable available to compose, you can set it on the host. If you do do

    SCRIPT=./tutorial_01/main.py docker-compose run --rm app env

    the script variable is set on the host, docker compose has access to it and your compose file will work as expected.

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