Connect to a Service Container in Github Actions

Increasingly there is a need to run containers during a github action build to run realistic tests. In my specific scenario I had a database integration test that I wanted to run against a postgres database with our latest database migrations applied.

We run our builds inside a multi-stage docker build so we actually need to have a build container communicate with the database container during the build phase. This is easy enough in the run phase but in the build phase there is just a flag you can pass to the build called network which takes an argument but the arguments it can take don’t appear to be documented anywhere. After significant trial and error I found that the argument it takes that we want is host. This will build the container using the host networking. As we surfaced the ports for postgres in our workflow file like so

postgres:
    image: postgres:15.3
    ports:
        - 5432:5432
    env:
        POSTGRES_DB: default
        POSTGRES_USER: webapp_user
        POSTGRES_PASSWORD: password
    options: >-
        --health-cmd pg_isready
        --health-interval 10s
        --health-timeout 5s
        --health-retries 5

We are able to access the database from the build context with 127.0.0.1. So we can pass in a variable to our container build

docker build --network=host . --tag ${{ env.DOCKER_REGISTRY_NAME }}/${{ env.DOCKER_IMAGE_NAME }}:${{ github.run_number }} --build-arg 'DATABASE_CONNECTION_STRING=${{ env.DATABASE_CONNECTION_STRING }}'

With all this in place the tests run nicely in the container during the build. Phew.