github actions: run multiple jobs in the same docker - docker

Question

I'm learning to deploy github actions to run multiple jobs with docker, and this is what I have so far:
github actions yml file is shown as follow. There are 2 jobs: job0 builds docker with Dockerfile0 and job1 builds docker with Dockerfile1.
# .github/workflows/main.yml
name: docker CI
on: push
jobs:
job0:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout#v2
- name: Build and Run
run: docker build . --file Dockerfile0 --tag job0
job1:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout#v2
- name: Build and Run
run: docker build . --file Dockerfile1 --tag job1
Dockerfile0 and Dockerfile1 share basically the same content, except for the argument in the last line:
FROM ubuntu:20.04
ADD . /docker_ci
RUN apt-get update -y
RUN apt-get install -y ... ...
WORKDIR /docker_ci
RUN python3 script.py <arg>
I wonder, can I build a docker for the 1st job, and then invoke multiple jobs execute command within the docker built from the 1st job? Thus I don't have to keep multiple Dockerfile and save some docker building time.
It would be better to build my docker locally from Dockerfile so I hope to avoid using container from docker hub.
runs-for-docker-actions looks relevant but I have trouble finding example deploying action locally (without publishing).

Answer 1

It definitely sounds like you should not build two different images - not for CI, and not for local development purposes (if it matters).
From the details you have provided, I would consider the following approach:
Define a Dockerfile with an ENTRYPOINT which is the lowest common denominator for your needs (it can be bash or python script.py).
In GitHub Actions, have a single job with multiple steps - one for building the image, and the others for running it with arguments.
For example:
FROM ubuntu
RUN apt-get update && apt-get install -y python3
WORKDIR /app
COPY script.py .
ENTRYPOINT ["python3", "script.py"]
This Dockerfile can be executed with any argument which will be passed on to the script.py entrypoint:
$ docker run --rm -it imagename some arguments
A sample GitHub Actions config might look like this:
jobs:
jobname:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout#v2
- name: Build the image
run: docker build --tag job .
- name: Test 1
run: docker run --rm -it job arg1
- name: Test 2
run: docker run --rm -it job arg2
If you insist on separating these to different jobs, as far as I understand it, your easiest option would still be to rebuild the image (but still using a single Dockerfile), since sharing a docker image built in one job, to another job, will be a more complicated task that I would recommend trying to avoid.