📝 Add automatic building of Docker containers

docs/productive/git/advanced/gitlab/docker.rst

@@ -0,0 +1,51 @@
+Building Docker containers
+==========================
+
+We use :doc:`ci-cd`, to create our Python Docker containers.
+
+#. First, we define the Python version in our :ref:`pyproject-toml` file of the
+   project:
+
+   .. code-block:: toml
+
+      [project]
+      name = "my-app"
+      requires-python = "==3.12.*"
+
+#. We then extract this string in our :file:`.gitlab-ci.yml` file and pass it as
+   a build argument to ``docker build``:
+
+   .. code-block:: yaml
+
+      build:
+        stage: build
+        only: [main]
+        script:
+          - export PY=$(sed -nE 's/^requires-python = "==(3\.[0-9]+)\.*"$/python\1/p' pyproject.toml)
+          - >
+            docker build
+            --build-arg PY=$PY
+
+#. Finally, we can use the extracted version in the Dockerfile to create a
+   virtual environment in the build phase and install the Python version in the
+   ``application`` stage:
+
+   .. code-block:: docker
+      :emphasize-lines: 3, 6
+
+      FROM your-docker/build-image as build
+
+      ARG PY
+      RUN --mount=type=cache,target=/root/.cache \
+          set -ex \
+          && virtualenv --python $PY /app
+      …
+      FROM your-docker/app-image
+      …
+      RUN set -ex \
+          && apt-get update -qy \
+          && apt-get install -qy \
+              -o APT::Install-Recommends=false \
+              -o APT::Install-Suggests=false \
+      …
+      COPY --from=build --chown=app /app /app

docs/productive/git/advanced/gitlab/index.rst

@@ -6,17 +6,20 @@ GitLab
 ======
 
 `GitLab <https://gitlab.com>`_ is a web application for version management based
-on Git. Later, further functions were added such as an issue tracking system with
-Kanban board, a system for `Continuous Integration and Continuous Delivery
+on Git. Later, further functions were added such as an issue tracking system
+with Kanban board, a system for `Continuous Integration and Continuous Delivery
 (CI/CD) <https://about.gitlab.com/features/continuous-integration/>`_ as well as
 a Wiki and Snippets. The GitLab Community Edition (CE) is developed as open
 source software under the MIT licence and can be installed on-premises.
 
 The GitLab CI tools enable automated builds and deployments without the need for
-external integrations. If a PaaS solution such as `Kubernetes
-<https://en.wikipedia.org/wiki/Kubernetes>`_ is already in use, apps can be
-automatically deployed, tested and scaled with GitLab CI/CD. In addition, code
-can be automatically scanned for potential security risks.
+external integrations, for example building a Docker container with the Python
+version of the project.
+
+If a PaaS solution such as `Kubernetes
+<https://en.wikipedia.org/wiki/Kubernetes>`_ is already in use, GitLab-CI/CD can
+be used to automatically deploy, test and scale apps. The
+:doc:`/productive/security` of your project can also be checked automatically.
 
 GitLab is a completely packaged platform, while GitHub can be extended with apps
 from the Marketplace. However, this does not mean that GitLab cannot be
@@ -32,5 +35,6 @@ integrated, for example with Asana, Jira, Microsoft Teams, Slack, etc.
    roles-permissions
    merge-requests
    ci-cd
+   docker
    github-migration
    package-registry