GitLab CI/CD for Docker in Docker

build_flask_service:
  image: docker:19.03.13
  stage: build
  services:
    - docker:19.03.13-dind
  variables:
    IMAGE_TAG_SHA: "$CI_REGISTRY_IMAGE/calculator_app/image:$CI_COMMIT_SHORT_SHA"      
    IMAGE_TAG: "$CI_REGISTRY_IMAGE/calculator_app/image:latest"     
  script:    
    - cd mse_flask_web_site/    
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY   
    - docker pull $IMAGE_TAG || true 
    - docker build -t $IMAGE_TAG_SHA -t $IMAGE_TAG .    
    - docker push $IMAGE_TAG_SHA    
    - docker push $IMAGE_TAG
  before_script:
    - docker info