GitLab CI example with private image registry

.gitlab-ci.yml

stages:
  - build
  - test
  - cleanup
  - tag

variables:
# don't do checkout unless we need to.
# Tests run on the code already present in the image which was just built.
  GIT_STRATEGY: none
  IMAGE_REPO: gcr.io/${CLOUDSDK_CORE_PROJECT}/app/${CI_COMMIT_REF_NAME}

## Globally defined variables for project:
## 1. CLOUDSDK_CORE_PROJECT, the GCP project id,
##    which is required for cloud-sdk image.
## 2. DOCKER_AUTH_CONFIG contains login credentials to private GCR.
## 3. GOOGLE_APPLICATION_CREDENTIALS contains base64-encoded 
##    service account file in JSON format.

.docker_build:
  image: docker:stable
  services:
    - docker:19.03.1-dind
  variables:
    GIT_STRATEGY: fetch
  before_script:
    - cat $GOOGLE_APPLICATION_CREDENTIALS
      | docker login -u _json_key --password-stdin https://gcr.io
  after_script:
    - docker logout gcr.io

.pytest:
  image: ${IMAGE_REPO}:${CI_COMMIT_SHORT_SHA}
  stage: test
  artifacts:
    reports:
      junit: test_results/*.xml

.gcloud:
  image: google/cloud-sdk:alpine
  before_script: 
  - cat $GOOGLE_APPLICATION_CREDENTIALS | gcloud auth activate-service-account --key-file -
  after_script:
  - gcloud auth revoke

build app:
  extends: .docker_build
  stage: build
  variables:
    GIT_STRATEGY: fetch
  script:
    - docker build
      --build-arg GIT_COMMIT=$CI_COMMIT_SHA
      --build-arg GIT_BRANCH=$CI_COMMIT_REF_NAME
      --build-arg BUILD_NUMBER=$CI_JOB_ID
      -t $IMAGE_REPO:${CI_COMMIT_SHORT_SHA}
      -f modules/app/docker/Dockerfile .
    - docker push $IMAGE_REPO:${CI_COMMIT_SHORT_SHA}

unit tests:
  extends: .pytest
  script:
    - pytest 
      --junit-xml=test_results/unit_tests.xml
      --color=yes
      -k 'unit_tests'
      modules/app/test

integration tests:
  extends: .pytest
  script:
    - pytest 
      --junit-xml=test_results/integration_tests.xml
      --color=yes
      -k 'integration_tests'
      modules/app/test

regression tests:
  extends: .pytest
  script:
    - pytest 
      --junit-xml=test_results/regression_tests.xml
      --color=yes
      -k 'regression_tests'
      modules/app/test

Delete failed image:
  extends: .gcloud
  stage: cleanup
  when: on_failure
  script:
    - gcloud container images delete
      ${IMAGE_REPO}:${CI_COMMIT_SHORT_SHA}

Tag latest:
  extends: .gcloud
  stage: tag
  when: on_success
  script:
    - gcloud container images add-tag
      ${IMAGE_REPO}:${CI_COMMIT_SHORT_SHA} ${IMAGE_REPO}:latest