GitLab CI/CD can be used with Docker to build Docker images.
For example, you can create a Docker image of your application and push it to a GitLab’s Container Registry.
In this note i am showing an example of how to create a new repository in GitLab with a CI/CD pipeline that will be used for building a “Hello World” Docker image and pushing it to a registry.
Cool Tip: Save username & password in Git credentials store! Read more →
GitLab CI/CD: Build Docker Image & Push to Registry
Create a new gitlab-build-docker-image Git repository, push it to GitLab and set up a remote origin (replace <username> in the URLs with your username):
$ mkdir gitlab-build-docker-image $ cd gitlab-build-docker-image $ git init $ touch .gitignore README.md $ git add -A $ git commit -m 'Initial commit' # for Git over HTTPS $ git push --set-upstream https://gitlab.com/<username>/gitlab-build-docker-image.git $ git remote add origin https://gitlab.com/<username>/gitlab-build-docker-image.git # for Git over SSH $ git push --set-upstream git@gitlab.com/<username>/gitlab-build-docker-image.git $ git remote add origin git@gitlab.com/<username>/gitlab-build-docker-image.git
Build Docker Image using GitLab CI/CD
Create a minimal Dockerfile at the root of your repository:
# Dockerfile
FROM alpine
RUN echo "Hello World"
At the same directory, create a .gitlab-ci.yml with the contents as follows:
# .gitlab-ci.yml variables: IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG # Tell 'docker:dind' to enable TLS (recommended) # and generate certificates in the specified directory. DOCKER_TLS_CERTDIR: "/certs" build-push-docker-image-job: # Specify a Docker image to run the job in. image: docker:latest # Specify an additional image 'docker:dind' ("Docker-in-Docker") that # will start up the Docker daemon when it is brought up by a runner. services: - docker:dind script: - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY - docker build -t $IMAGE_TAG . - docker push $IMAGE_TAG
The pipeline in the example above is building a Docker image from the Dockerfile created earlier and pushes it to the project’s Container Registry.
It uses the following GitLab’s predefined variables:
| Environment variable | Description |
|---|---|
CI_REGISTRY_IMAGE |
The address of the project’s Container Registry. |
CI_COMMIT_REF_SLUG |
The branch or tag name for which project is built – in lowercase, shortened to 63 bytes, and with everything except 0-9 and a-z replaced with -. |
CI_REGISTRY |
The address of the GitLab Container Registry. This variable includes a :port value if one is specified in the registry configuration. |
CI_REGISTRY_USER |
The username to push containers to the project’s GitLab Container Registry. |
CI_REGISTRY_PASSWORD |
The password to push containers to the project’s GitLab Container Registry. This password value is the same as the CI_JOB_TOKEN and is valid only as long as the job is running. Use the CI_DEPLOY_PASSWORD for long-lived access to the registry. |
Cool Tip: Print all environment variables in GitLab CI/CD! Read more →