GitLab: How to build a docker image and run tests or generate documentation using the image

$README.md

How to build a docker image and run tests or generate documentation using the image with GitLab

Let's say you have a ruby project. You write tests using rspec and you write documentation inside the code. And you are using awesome GitLab to host your git repo, run CI pipelines and store your docker images in registry.

Build an image.

First we need to build an image. But we want to leverage docker layer caching, because libraries (rubygems) doesn't update very often. That's why we do docker pull first, and docker build --cache-from after.

If you make a feature branch and update some libraries, you can't use layer with libraries form the master branch. That's why we try to docker pull for feature branch first, and docker pull for master branch after.

And we push built image after to the registry.

Run tests

We use our just built image by setting image for the job. We already have the code inside the image and we don't need to check it out again.

BUT there is a gotcha, current working directory is $CI_PROJECT_DIR and our source code lays in /app. Do cd /app in before_script.

Publish yard documentation with GitLab Pages

When GitLab runner starts a job with you image, it creates a project directory on the host, run a new docker container with the image and mounts project directory as a volume.

After pages is generated, GitLab waits for it in the project directory, that's why we need to move the docs from our docker container to the project directory.

#docker #gitlab-ci

.gitlab-ci.yml

image: docker:git

before_script:
  - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN $CI_REGISTRY

variables:
  CONTAINER_BRANCH_IMAGE: $CI_REGISTRY/$CI_PROJECT_PATH:$CI_COMMIT_REF_SLUG
  CONTAINER_MASTER_IMAGE: $CI_REGISTRY/$CI_PROJECT_PATH:master

stages:
  - build
  - test

build:
  stage: build
  script:
    - >
     if docker pull $CONTAINER_BRANCH_IMAGE; then
       export CONTAINER_CACHE_IMAGE=$CONTAINER_BRANCH_IMAGE
     else
       docker pull $CONTAINER_MASTER_IMAGE || true
       export CONTAINER_CACHE_IMAGE=$CONTAINER_MASTER_IMAGE
     fi
    - docker build --cache-from $CONTAINER_CACHE_IMAGE -t $CONTAINER_BRANCH_IMAGE .
    - docker push $CONTAINER_BRANCH_IMAGE

.init-image: &base
  image: "$CONTAINER_BRANCH_IMAGE"
  variables:
    GIT_STRATEGY: none
  before_script:
    - cd /app
    - cp config/database.yml.sample config/database.yml
    - cp config/redis.yml.sample config/redis.yml

rspec:
  <<: *base
  stage: test
  script:
    - bundle exec rspec

rubocop:
  <<: *base
  stage: test
  script:
    - bundle exec rake style

pages:
  <<: *base
  script:
    - bundle exec yard
    - rm -rf $CI_PROJECT_DIR/public && mkdir -p $CI_PROJECT_DIR/public
    - cp -r  doc/* $CI_PROJECT_DIR/public/
  artifacts:
    paths:
    - public
  only:
    - master

Dockerfile

FROM ruby:2.5.7

ENV LANG C.UTF-8
ENV RAILS_ROOT /app

WORKDIR /app

# Make an image layer with libraries, this will speed up consecutive builds 
COPY Gemfile* ./
COPY vendor/ ./vendor/
RUN bundle install

COPY . .