Merge branch 'improve-ci-config' into 'master'

Improve CI/CD configuration

Closes #83 and #84

See merge request dorie/dorie!76

(cherry picked from commit 0557af13)

.gitlab-ci.yml

@@ -28,7 +28,8 @@ stages:
 setup:dune-env: &setup
   stage: setup
   only:
-    - web # activate through 'Run pipeline' only.
+    variables:
+      - $REBUILD_BASE_IMAGE # must be defined and have non-empty value
   tags:
     - dind
   image: docker:stable
@@ -170,6 +171,7 @@ deploy:dockerhub-devel: &deploy
     - docker:dind
   variables:
     DOCKER_DRIVER: overlay2
+  dependencies: []
   before_script:
     - $DOCKER_LOGIN
   script:

docker/README.md

+# DORiE Docker Images
+
+DORiE uses [Docker](https://www.docker.com/) images for testing and deploying
+applications. These images are publicly available from
+[Docker Hub](https://hub.docker.com/). There are two repositories:
+
+* [`dorie/dorie`](https://hub.docker.com/r/dorie/dorie/): The DORiE application.
+* [`dorie/dune-env`](https://hub.docker.com/r/dorie/dune-env/): The DUNE
+    environment image.
+
+`dune-env` is used for compiling DORiE in a 'clean' Ubuntu environment where all
+dependencies are already installed. The final DORiE application image is the
+DUNE image with DORiE installed.
+
+We differentiate between two base images, one where DUNE is compiled with GCC,
+and one where it is compiled with Clang.
+
+## GitLab CI configuration
+
+Both images are updated by the GitLab CI/CD Pipeline defined in
+[`.gitlab-ci.yml`](../gitlab-ci.yml).
+
+The `setup` build stage is builds a new DUNE environment image "from scratch".
+It is triggered by running a pipeline with the CI variable `REBUILD_BASE_IMAGE`
+set to a non-empty value. This is achieved by manually starting the pipeline
+from the GitLab web interface ("CI/CD" - "Pipelines" - "Run Pipeline") and
+entering the variable as well as an arbitrary value. This should only be
+necessary if dependencies or their required versions change.
+
+The `prep` stage updates all APT and DUNE packages in the DUNE environment image
+and is run whenever a pipeline includes the deployment of a new application
+image.
+
+The `deploy` stage deploys DORiE application images. It compiles DORiE into the
+DUNE environment image. This stage is only run if tags are pushed or commits
+are pushed to `master`.
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