Example Gitlab CI Config for a Rails + Nginx application using Docker Compose

.gitlab-ci.yml

# See how variables work, and a list of predefined ones:
#  - https://docs.gitlab.com/ce/ci/variables/
variables:
  RAILS_IMAGE: registry.gitlab.com/bryanbraun/gridmaster.io/railsapp:$CI_COMMIT_SHA
  NGINX_IMAGE: registry.gitlab.com/bryanbraun/gridmaster.io/nginx:$CI_COMMIT_SHA
  DEPLOY_TAG: $CI_COMMIT_SHA

cache:
  paths:
  - vendor/ruby

# See the following multi-stage set up examples:
#   https://docs.gitlab.com/ce/ci/docker/using_docker_build.html#using-the-gitlab-container-registry
#   https://gist.github.com/jorge07/63b993e8f934012a5abb6b55cc702c75
stages:
  - test
  - build
  - deploy

test_job:
  stage: test
  image: ruby:2.3.4
  services:
    - postgres:9.6.1
  artifacts:
    paths:
      - public/
    expire_in: 12 hrs
  variables:
    RAILS_ENV: test
    POSTGRES_DB: gridmaster_test
    POSTGRES_USER: postgres
    POSTGRES_PASSWORD: ''
  before_script:
    # we install gems and precompile assets now so both the NGINX & RAILS images have a copy
    # of the static assets for baked into their images. For why, see "Compiling Assets" at:
    # http://chrisstump.online/2016/03/17/continuous-deployment-docker-rails/
    - bundle install --jobs $(nproc) --path vendor
    - rails assets:precompile
  script:
    - ls -al public/assets # for debugging
    - rails db:test:prepare
    - rails test

# We a "docker-in-docker" image, to run docker on CI like we do in dev. See:
#  - https://docs.gitlab.com/ce/ci/docker/using_docker_build.html#use-docker-in-docker-executor
#  - http://stackoverflow.com/a/40387216/1154642
build_job:
  stage: build
  image: docker:latest
  services:
    - docker:dind
  before_script:
    - touch .env # prevents an error where docker-compose tries to move a non-existant file.
  variables:
    # We use the overlay driver for improved performance.
    # See: https://docs.gitlab.com/ce/ci/docker/using_docker_build.html#using-the-overlayfs-driver
    DOCKER_DRIVER: overlay
    RAILS_ENV: production
  script:
    - ls -al public/assets # for debugging
    - docker build -t $RAILS_IMAGE .
    - docker build -f config/containers/Dockerfile-nginx -t $NGINX_IMAGE .
    - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN https://registry.gitlab.com
    - docker push $NGINX_IMAGE
    - docker push $RAILS_IMAGE
    # I'm not pushing postgres images because I simply use the official Postgres image.
    # The other images contain precompiled assets and should be built every time.
  only:
    - master

# This job triggers a rake task containing a deploy script. For ideas on deploys scripts, see:
# - http://chrisstump.online/2016/03/17/continuous-deployment-docker-rails/
# Gitlab ones:
# - https://www.stavros.io/posts/how-deploy-django-docker
deploy_job:
  stage: deploy
  image: ruby:2.3.4
  variables:
    RAILS_ENV: test
  environment:
    name: production
    url: https://gridmaster.io
  before_script:
    # We'll access our production server via SSH keys. See
    # https://docs.gitlab.com/ee/ci/ssh_keys/README.html#using-ssh-keys for details.
    # install ssh-agent
    - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
    # run ssh-agent
    - eval $(ssh-agent -s)
    # add ssh key stored in SSH_PRIVATE_KEY variable to the agent store
    - ssh-add <(echo "$SSH_PRIVATE_KEY")
  script:
    - bundle install --jobs $(nproc) --path vendor
    - bundle exec rails docker:deploy
  when: manual
  only:
    - master