Building Docker containers with Gitlab

This tutorial shows how to set up the basic GitLab pipeline to automaticaly build Docker image and publish it to a container registry.

Prerequisites

• Gitlab repository
• Dockerfile in the repository with desired container configuration

Configure CI/CD Gitlab Pipeline file

• In your desired repository, use Set up CI/CD button as shown in the following image.

• In the .gitlab-ci.yml editor copy and paste following snippet:

docker-build:
  image: docker:latest
  stage: build
  services:
    - docker:dind
  before_script:
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
  script:
    - |
      if [[ "$CI_COMMIT_BRANCH" == "$CI_DEFAULT_BRANCH" ]]; then
        tag=""
        echo "Running on default branch '$CI_DEFAULT_BRANCH': tag = 'latest'"
      else
        tag=":$CI_COMMIT_REF_SLUG"
        echo "Running on branch '$CI_COMMIT_BRANCH': tag = $tag"
      fi
    - docker build --pull -t "$CI_REGISTRY_IMAGE${tag}" .
    - docker push "$CI_REGISTRY_IMAGE${tag}"
  rules:
    - if: $CI_COMMIT_BRANCH
      exists:
        - Dockerfile

This will use the standard Gitlab Container Registry available within your own project. Note the variable $CI_REGISTRY, which is specific for the repository.

• Commit changes

• Pipeline will be triggered and it’s status could be shown within the last commit information. For list of jobs for given pipeline visit CI/CD > Pipelines

If pipeline job succeeds, the freshly built container image will be uploaded to Gitlab’s container registry.
The Packages & Registries > Container registry is available here:

For advanced information please refer to the official documentation

How to use images from Gitlab Registry

If the project’s visibility within GitLab is public and container registry is not limited to authenticated users, simply use:

docker run [options] registry.example.com/group/project/image [arguments]

If you are using MUNI ICS GitLab, the registry URL is: registry.gitlab.ics.muni.cz

If project visibility or container registry are set to private, authentication to container registry is needed. You will need to create deploy token and use it as descibed in the official documentation

For more information please refer to official documentation.

Upload image to custom container registry

Change the options of docker login command in before_script part of your definition of pipeline (gitlab-ci.yml).

  before_script:
    - docker login -u "username" -p "password" example.io