I have a Gitlab CI pipeline to build and publish a Docker container. I want to push the container image to an undefined number (“N”) of repositories. I originally had something like this:

build-and-push:
  image: docker:cli
  services:
    - docker:dind
  parallel:
    matrix:
      - REGISTRY: $REGISTRY1
        USERNAME: $USER1
        PASSWORD: $PASS1
      - REGISTRY: $REGISTRY2
        USERNAME: $USER2
        PASSWORD: $PASS2
  script: |
    docker build --file Dockerfile --tag "$REGISTRY/my-image" .
    echo "$PASSWORD" | docker login --username "$USERNAME" --password-stdin "$REGISTRY"
    docker push "$REGISTRY/my-image"

But this does the docker build for each job, which takes some time and it’s unnecessary to duplicate that part when I only want the docker push part duplicated.

I tried doing docker build in one job and docker push in a subsequent job. But in the second job it sometimes locally sees the image built in the first job, and sometimes it doesn’t (not sure why).

I considered saving to artifacts as a tar file and passing that to docker import/push, but those images can get to multiple GB which seems like overkill for an artifact.

So what’s the right approach here?