Building multi arch container images with GitLab pipelines.

Goal is to build multi arch images for amd64 and arm64 platforms by leveraging GitLab CI.

arm64 platform specific image can be levereged by AWS Graviton, a 64-bit ARM-based CPU.

Here I’ll elluminate the steps and relevant commands:

1. Install buildx cli plugin into gitlab runner docker executor image

• Buildx installation is required for capability to create and manage builders.

#Install docker buildx cli plugin
RUN mkdir -p $HOME/.docker/cli-plugins && \
    wget -O $HOME/.docker/cli-plugins/docker-buildx https://github.com/docker/buildx/releases/tag/v0.10.5/buildx-v0.10.5.linux-amd64 && \
    chmod +x $HOME/.docker/cli-plugins/docker-buildxd

2. GitLab pipeline bits

• key points are to declare variables required for the job and set image for gitlab runner executor

variables:
  REGISTRY_IMAGE: "ecr.region.amazonaws.com/your-repository"
  PLATFORM_ARCHITECTURE: "amd64"
...
release:docker-image:
  image: your-choice-container-registry/repository/docker-executor-image:latest # Container image build in step 1
  stage: release
  script:
    - ./gradlew release --project-prop tag=${CI_COMMIT_TAG} --project-prop image=${REGISTRY_IMAGE} --project-prop arch=${PLATFORM_ARCHITECTURE}

3. Gradle task bits

• Gradle build tool is matter of choice. Gradle wrapper takes care of prerequisites like builder creation and management as well as the actual container image building process.
• release task consists of two parts: creation of builder instance and the actual platform specific container image build process

task release() {
    doLast {
        exec {
            workingDir './'
            executable 'docker'
            args 'buildx', 'create', '--name', 'multiarch-builder', '--driver', 'docker-container'
        }
        exec {
            workingDir './'
            executable 'docker'
            args 'buildx', 'use', 'multiarch-builder'
        }
        exec {
            workingDir './'
            executable 'docker'
            args 'buildx', 'inspect', '--bootstrap'
        }
        exec {
            workingDir './'
            executable 'docker'
            args = ['buildx', 'build', '-t', "$image/$arch:$tag", '-t', "$image/$arch:latest", '--platform', "linux/$arch", '--push', '--progress', 'plain', '.']
        }
    }
}

For your convenience here are the same commands listed above but in a generic form.

• Create builder instance

docker buildx create --name multiarch-builder --driver docker-container
docker buildx use multiarch-builder
docker buildx inspect --bootstrap

• Build the actual platform specific container image

docker buildx build -t $image/$arch:$tag -t $image/$arch:latest --platform linux/$arch --push --progress plain .