build:docker:
  image: docker:20-dind
  variables:
    # using "docker" as the host is only possible if you alias the service below
    DOCKER_HOST: tcp://docker:2375
    # could be wrong here but although Docker defaults to overlay2,
    # Docker-in-Docker (DIND) does not according to the following GitLab doc:
    # https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#use-the-overlayfs-driver
    DOCKER_DRIVER: overlay2
    DOCKER_TLS_CERTDIR: ""
  services:
    - name: docker:20-dind
      alias: docker
      # in our experience although you'd assume this would be sufficient, this did
      # nothing to prevent connection errors without `DOCKER_TLS_CERTDIR` being set
      # to an empty string, and I would call that beyond mildly infuriating.
      command: ["--tls=false"]
  before_script:
    - echo ${REGISTRY_PASSWORD} | docker login ${REGISTRY} -u ${REGISTRY_USER} --
  password-stdin
    - *version_info
  script:
    - docker build .
      --tag ${CONTAINER_IMAGE}:$BUILD_VERSION
      --tag ${CONTAINER_IMAGE}:latest
    - docker push ${CONTAINER_IMAGE}:latest
    - docker push ${CONTAINER_IMAGE}:$BUILD_VERSION