GitLab Documentation

Using Docker Build

GitLab CI allows you to use Docker Engine to build and test docker-based projects.

This also allows to you to use docker-compose and other docker-enabled tools.

One of the new trends in Continuous Integration/Deployment is to:

  1. create an application image,
  2. run tests against the created image,
  3. push image to a remote registry, and
  4. deploy to a server from the pushed image.

It's also useful when your application already has the Dockerfile that can be used to create and test an image:

$ docker build -t my-image dockerfiles/
$ docker run my-docker-image /script/to/run/tests
$ docker tag my-image my-registry:5000/my-image
$ docker push my-registry:5000/my-image

This requires special configuration of GitLab Runner to enable docker support during jobs.

Runner Configuration

There are three methods to enable the use of docker build and docker run during jobs; each with their own tradeoffs.

Use shell executor

The simplest approach is to install GitLab Runner in shell execution mode. GitLab Runner then executes job scripts as the gitlab-runner user.

  1. Install GitLab Runner.

  2. During GitLab Runner installation select shell as method of executing job scripts or use command:

    sudo gitlab-ci-multi-runner register -n \
      --url https://gitlab.com/ci \
      --registration-token REGISTRATION_TOKEN \
      --executor shell \
      --description "My Runner"
    
  3. Install Docker Engine on server.

    For more information how to install Docker Engine on different systems checkout the Supported installations.

  4. Add gitlab-runner user to docker group:

    sudo usermod -aG docker gitlab-runner
    
  5. Verify that gitlab-runner has access to Docker:

    sudo -u gitlab-runner -H docker info
    

    You can now verify that everything works by adding docker info to .gitlab-ci.yml:

    before_script:
      - docker info
    
    build_image:
      script:
        - docker build -t my-docker-image .
        - docker run my-docker-image /script/to/run/tests
    
  6. You can now use docker command and install docker-compose if needed.

Note:

Use docker-in-docker executor

The second approach is to use the special docker-in-docker (dind) Docker image with all tools installed (docker and docker-compose) and run the job script in context of that image in privileged mode.

In order to do that, follow the steps:

  1. Install GitLab Runner.

  2. Register GitLab Runner from the command line to use docker and privileged mode:

    sudo gitlab-ci-multi-runner register -n \
      --url https://gitlab.com/ci \
      --registration-token REGISTRATION_TOKEN \
      --executor docker \
      --description "My Docker Runner" \
      --docker-image "docker:latest" \
      --docker-privileged
    

    The above command will register a new Runner to use the special docker:latest image which is provided by Docker. Notice that it's using the privileged mode to start the build and service containers. If you want to use docker-in-docker mode, you always have to use privileged = true in your Docker containers.

    The above command will create a config.toml entry similar to this:

    [[runners]]
      url = "https://gitlab.com/ci"
      token = TOKEN
      executor = "docker"
      [runners.docker]
        tls_verify = false
        image = "docker:latest"
        privileged = true
        disable_cache = false
        volumes = ["/cache"]
      [runners.cache]
        Insecure = false
    
  3. You can now use docker in the build script (note the inclusion of the docker:dind service):

    image: docker:latest
    
    # When using dind, it's wise to use the overlayfs driver for
    # improved performance.
    variables:
      DOCKER_DRIVER: overlay
    
    services:
    - docker:dind
    
    before_script:
    - docker info
    
    build:
      stage: build
      script:
      - docker build -t my-docker-image .
      - docker run my-docker-image /script/to/run/tests
    

Docker-in-Docker works well, and is the recommended configuration, but it is not without its own challenges:

An example project using this approach can be found here: https://gitlab.com/gitlab-examples/docker.

Use Docker socket binding

The third approach is to bind-mount /var/run/docker.sock into the container so that docker is available in the context of that image.

In order to do that, follow the steps:

  1. Install GitLab Runner.

  2. Register GitLab Runner from the command line to use docker and share /var/run/docker.sock:

    sudo gitlab-ci-multi-runner register -n \
      --url https://gitlab.com/ci \
      --registration-token REGISTRATION_TOKEN \
      --executor docker \
      --description "My Docker Runner" \
      --docker-image "docker:latest" \
      --docker-volumes /var/run/docker.sock:/var/run/docker.sock
    

    The above command will register a new Runner to use the special docker:latest image which is provided by Docker. Notice that it's using the Docker daemon of the Runner itself, and any containers spawned by docker commands will be siblings of the Runner rather than children of the runner. This may have complications and limitations that are unsuitable for your workflow.

    The above command will create a config.toml entry similar to this:

    [[runners]]
      url = "https://gitlab.com/ci"
      token = REGISTRATION_TOKEN
      executor = "docker"
      [runners.docker]
        tls_verify = false
        image = "docker:latest"
        privileged = false
        disable_cache = false
        volumes = ["/var/run/docker.sock:/var/run/docker.sock", "/cache"]
      [runners.cache]
        Insecure = false
    
  3. You can now use docker in the build script (note that you don't need to include the docker:dind service as when using the Docker in Docker executor):

    image: docker:latest
    
    before_script:
    - docker info
    
    build:
      stage: build
      script:
      - docker build -t my-docker-image .
      - docker run my-docker-image /script/to/run/tests
    

While the above method avoids using Docker in privileged mode, you should be aware of the following implications:

Using the OverlayFS driver

By default, when using docker:dind, Docker uses the vfs storage driver which copies the filesystem on every run. This is a very disk-intensive operation which can be avoided if a different driver is used, for example overlay.

  1. Make sure a recent kernel is used, preferably >= 4.2.
  2. Check whether the overlay module is loaded:

    sudo lsmod | grep overlay
    

    If you see no result, then it isn't loaded. To load it use:

    sudo modprobe overlay
    

    If everything went fine, you need to make sure module is loaded on reboot. On Ubuntu systems, this is done by editing /etc/modules. Just add the following line into it:

    overlay
    
  3. Use the driver by defining a variable at the top of your .gitlab-ci.yml:

    variables:
      DOCKER_DRIVER: overlay
    

Using the GitLab Container Registry

Notes:

  • This feature requires GitLab 8.8 and GitLab Runner 1.2.
  • Starting from GitLab 8.12, if you have 2FA enabled in your account, you need to pass a personal access token instead of your password in order to login to GitLab's Container Registry.

Once you've built a Docker image, you can push it up to the built-in GitLab Container Registry. For example, if you're using docker-in-docker on your runners, this is how your .gitlab-ci.yml could look like:

 build:
   image: docker:latest
   services:
   - docker:dind
   stage: build
   script:
     - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN registry.example.com
     - docker build -t registry.example.com/group/project/image:latest .
     - docker push registry.example.com/group/project/image:latest

You have to use the special gitlab-ci-token user created for you in order to push to the Registry connected to your project. Its password is provided in the $CI_JOB_TOKEN variable. This allows you to automate building and deployment of your Docker images.

You can also make use of other variables to avoid hardcoding:

services:
  - docker:dind

variables:
  IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME

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

build:
  stage: build
  script:
    - docker build -t $IMAGE_TAG .
    - docker push $IMAGE_TAG

Here, $CI_REGISTRY_IMAGE would be resolved to the address of the registry tied to this project, and $CI_COMMIT_REF_NAME would be resolved to the branch or tag name for this particular job. We also declare our own variable, $IMAGE_TAG, combining the two to save us some typing in the script section.

Here's a more elaborate example that splits up the tasks into 4 pipeline stages, including two tests that run in parallel. The build is stored in the container registry and used by subsequent stages, downloading the image when needed. Changes to master also get tagged as latest and deployed using an application-specific deploy script:

image: docker:latest
services:
- docker:dind

stages:
- build
- test
- release
- deploy

variables:
  CONTAINER_TEST_IMAGE: registry.example.com/my-group/my-project/my-image:$CI_COMMIT_REF_NAME
  CONTAINER_RELEASE_IMAGE: registry.example.com/my-group/my-project/my-image:latest

before_script:
  - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN registry.example.com

build:
  stage: build
  script:
    - docker build --pull -t $CONTAINER_TEST_IMAGE .
    - docker push $CONTAINER_TEST_IMAGE

test1:
  stage: test
  script:
    - docker pull $CONTAINER_TEST_IMAGE
    - docker run $CONTAINER_TEST_IMAGE /script/to/run/tests

test2:
  stage: test
  script:
    - docker pull $CONTAINER_TEST_IMAGE
    - docker run $CONTAINER_TEST_IMAGE /script/to/run/another/test

release-image:
  stage: release
  script:
    - docker pull $CONTAINER_TEST_IMAGE
    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
    - docker push $CONTAINER_RELEASE_IMAGE
  only:
    - master

deploy:
  stage: deploy
  script:
    - ./deploy.sh
  only:
    - master

Some things you should be aware of when using the Container Registry: