在 docker 容器内启动 cron 服务

Question

I'm trying to run a cron job inside a Docker container housing my backend microservice. The cron job is being modified through a FastAPI call. But, although the job is being created, it is not getting executed. In fact, after accessing the terminal using docker exec -it bash my_container , I tried to add a dummy cron job manually but even that is not getting executed. I checked status using service cron status and it says [ ok ] cron is running.

Dockerfile:

FROM tiangolo/uvicorn-gunicorn-fastapi:python3.7

# Install dependencies:
COPY requirements.txt .
RUN pip3 install -r requirements.txt

RUN apt-get update
RUN apt-get install cron
RUN service cron start

COPY ./app /app

Please help me out.

Answer 1

I would suggest creating a docker container that will run this single task. Then using something like Jenkins to schedule the tasks which will create the container, run the tasks, then close.

This way you'll have some visibility into the status of the tasks. Have they run? Was it a success?

Answer 2

This is a common problem and results from:

• Difference between images and containers
• Running single (??) processes in containers

The RUN service cron start statement is executed during the image build not the container run.

To run cron at container run, you are best placed creating a shell script that includes everything you want to run:

ENTRYPOINT ["bash", "-c", "service cron start && /app"]

NOTE convention is to have a script called ./entrypoint.sh but I've shown the commands in-line for simplicity.

Be aware that you'll then be running a script that runs your process and this may affect processing of signals by the container etc.