Want to run python script and Flask api from single Dockerfile

Question

I am trying to create container with following docker file. Since it is going to execute last CMD, it ignores CMD ["sh", "-c", "python3 run_scheduler.py --config=${config}"]. Is there a way to run both from single docker file. Also, is it possible to pass ${config} argument to flask api in CMD ["gunicorn", "--bind", "0.0.0.0:5000", "run_api:application", "&"]

FROM python:3.8

LABEL version="0.1"

WORKDIR /app
COPY . /app

ARG config=dev
RUN  pip install -r requirements.txt
EXPOSE 5000
CMD ["sh", "-c", "python3 run_scheduler.py --config=${config}"]
CMD ["gunicorn",  "--bind", "0.0.0.0:5000",  "run_api:application", "&"]

Check out this SO Post: serverfault.com/questions/685697/… — dfundako
– dfundako, Commented Jun 10, 2020 at 13:49
You can specify an alternate command when you run the container (after the image name in docker run; as a Docker Compose command:). Run two separate containers with two separate commands. — David Maze
– David Maze, Commented Jun 10, 2020 at 14:14

Grzegorz Pudłowski · Accepted Answer · 2020-06-10 15:35:58Z

1

As mentioned in comments you can pass 2-line bash script in CMD. This can cause problems however. Docker is not really meant to run multiple processes in single container. I already see "&" argument in your second CMD. I guess you had problems with second process wasn't running so you tried to push it to the background.

The solution recommended by Docker is to run supervisord inside the container: https://docs.docker.com/config/containers/multi-service_container/

From naming concepts I guess you can solve your problem with Flask-APScheduler https://github.com/viniciuschiele/flask-apscheduler This way you can get rid of second sidecar script.

And lastly you asked:

Also, is it possible to pass ${config} argument to flask api

and answer is yes. Declare ENV in your Dockerfile like so:

FROM python:3.8
...
...
ENV config foo
...
CMD ["whatever_command", "--option", "${config}"]

This way "${config}" will be replaced with value foo.

answered Jun 10, 2020 at 15:35

Grzegorz Pudłowski

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4 Comments

Rajan Sharma Over a year ago

Thanks for help. I did create 2 containers. Worked for my use case.using following docker compose.

version: '3' services:   api:     build:       context: .       dockerfile: Dockerfile     command: ["gunicorn",  "--bind", "0.0.0.0:5000",  "run_api:application", "&"]     ports:       - "5000:5000"   scheduler:     build:       context: .       dockerfile: Dockerfile     command: ["sh", "-c", "python3 run_scheduler.py --config=dev"]     ports:       - "80:80"

Rajan Sharma Over a year ago

I also need to pass --config=dev to command: ["gunicorn", "--bind", "0.0.0.0:5000", "run_api:application", "&"] . This variable I need to use to pick config in Flask Api. I know that I can pass this as an arg from command but how can I access in my flask api (run_api: application).

Grzegorz Pudłowski Over a year ago

You need to use os module: from os import getenv and use getenv to pick up your env var. Have a look at docs.python.org/3.8/library/os.html#os.getenv

Rajan Sharma Over a year ago

Thanks, "from os import getenv and use getenv" did solve the issue.

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