image: docker:19
services:
  - docker:19-dind
variables:
  DOCKER_DRIVER: overlay
  DOCKER_TLS_CERTDIR: ""
stages:
  - buildx
  - build
  - push

buildx:
  image: docker:19-git
  stage: buildx
  variables:
    GIT_STRATEGY: none
  artifacts:
    paths:
      - buildx
    expire_in: 1 hour
  services:
    - docker:19-dind
  script:
    - export DOCKER_BUILDKIT=1
    - git clone git://github.com/docker/buildx ./docker-buildx
    - docker build --platform=local -o . ./docker-buildx

build:
  image: docker:19
  stage: build
  services:
    - name: docker:19-dind
      command: ["--experimental"]
  before_script:
    - mkdir -p ~/.docker/cli-plugins
    - mv buildx ~/.docker/cli-plugins/docker-buildx
    - docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
  variables:
    IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
  script:
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
    - docker buildx create --use --name mybuilder
    - docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 --push -t $IMAGE_TAG .

Push latest:
  variables:
    # We are just playing with Docker here. 
    # We do not need GitLab to clone the source code.
    GIT_STRATEGY: none
  stage: push
  only:
    # Only "main" should be tagged "latest"
    - main
  script:
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
    # Because we have no guarantee that this job will be picked up by the same runner 
    # that built the image in the previous step, we pull it again locally
    - docker pull --platform linux/amd64,linux/arm64,linux/arm/v7 $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
    # Then we tag it "latest"
    - docker tag --platform linux/amd64,linux/arm64,linux/arm/v7 $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME $CI_REGISTRY_IMAGE:latest
    # Annnd we push it.
    - docker push --platform linux/amd64,linux/arm64,linux/arm/v7 $CI_REGISTRY_IMAGE:latest

# Finally, the goal here is to Docker tag any Git tag
# GitLab will start a new pipeline everytime a Git tag is created, which is pretty awesome
Push tag:
  variables:
    # Again, we do not need the source code here. Just playing with Docker.
    GIT_STRATEGY: none
  stage: push
  only:
    # We want this job to be run on tags only.
    - tags
  script:
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
    - docker pull $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME