Automatic deployment of Google App Engine project with Gitlab Continuous Integration - https://medium.com/evenbit/an-easy-guide-to-automatically-deploy-your-google-app-engine-project-with-gitlab-ci-48cb84757125

.gitlab-ci.yml

image: python:2.7

before_script:
  - echo "deb http://packages.cloud.google.com/apt cloud-sdk-jessie main" | tee /etc/apt/sources.list.d/google-cloud-sdk.list
  - curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
  - apt-get update && apt-get install google-cloud-sdk

after_script:
  - rm /tmp/$CI_PIPELINE_ID.json

deploy_production:
  stage: deploy
  environment: Production
  only:
    - master
  script:
    - echo $DEPLOY_KEY_FILE_PRODUCTION > /tmp/$CI_PIPELINE_ID.json
    - gcloud auth activate-service-account --key-file /tmp/$CI_PIPELINE_ID.json
    - gcloud --quiet --project $PROJECT_ID_PRODUCTION app deploy