Building Docker Images

New Allpix Squared Docker images are automatically created and deployed by the CI for every new tag and as a nightly build from the master branch. New versions are published to project Docker container registry [@ap2-container-registry]. Tagged versions can be found via their respective tag name, while updates via the nightly build are always stored with the latest tag attached.

The final Docker image is formed from two consecutive images with different layers of software added. The deps image contains all build dependencies such as compilers, CMake, and git as well as the two main dependencies of the framework are ROOT6 and Geant4. It derives from the latest Ubuntu LTS Docker image and can be build using the etc/docker/Dockerfile.deps file via the following commands:

docker build --file etc/docker/Dockerfile.deps            \
             --tag gitlab-registry.cern.ch/allpix-squared/\
             allpix-squared/allpix-squared-deps:vX        \
             .
docker push gitlab-registry.cern.ch/allpix-squared/\
            allpix-squared/allpix-squared-deps

This image is created manually and only updated when necessary, i.e. if major new version of the underlying dependencies are available. The placeholder vX is a version number which should be incremented when applying changes or updating software versions in the deps Docker image. This version number should subsequently also be adjusted in the CI pipeline (.gitlab-ci.yml) and the Allpix Squared Docker file (/etc/docker/Dockerfile) so that the correct dependencies image is picked up.

Important

The Docker image containing the dependencies should not be flattened with commands like

docker export <container id> | docker import - <tag name>

because it strips any ENV variables set or used during the build process. They are used to set up the ROOT6 and Geant4 environments. When flattening, their executables and data paths cannot be found in the final Allpix Squared image.

Finally, the latest revision of Allpix Squared is built using the file etc/docker/Dockerfile. This job is performed automatically by the continuous integration and the created containers are directly uploaded to the project’s Docker registry:

docker build --file etc/docker/Dockerfile                                \
             --tag gitlab-registry.cern.ch/allpix-squared/allpix-squared \
             .

A short summary of potential use cases for Docker images is provided in Section 2.7.