Docker 

The following is an example .gitlab-ci.yml file demonstrating a container build using the common Docker-in-Docker technique. For a variety of reasons, including performance, the DinD storage is placed in memory and is limited by the service container memory (default of 2Gi unless changed via service_memory). If more is needed for, large images, increase it as shown.

container:
  stage: build
  variables:
    DOCKER_VERSION: 28.0.2
    DOCKER_HOST: tcp://docker:2375
    DOCKER_TLS_CERTDIR: ""
  services:
    - name: docker:${DOCKER_VERSION}-dind
      alias: docker
      command: ["--tls=false"]
      variables:
        KUBERNETES_SERVICE_MEMORY_REQUEST: "8Gi"
  image: docker:${DOCKER_VERSION}
  script: docker buildx build .

Workflow 

Instead of the common approach of building everything in a Dockerfile it is generally preferred to build the application outside the container build process and copy the result into the container. Builds on the outside will benefit from the Intelligent Cache and thus be more performant and reliable.

For those already avoiding the build layers ending up in the final image using a multistage build this approach simply moves the first build into the CI job and copies from the build context.

For example, a multistage build like the following:

FROM toolchain:1.2.3 as build
RUN install_dependencies
RUN compile

FROM scratch
COPY --from=build /app /app

Becomes:

container:
  # ...
  image: toolchain:1.2.3
  script:
    - install_dependencies
    - compile
    - docker buildx build .

FROM scratch
COPY app /app