Build docker images with gitlab CI

These will be pushed to gitlab's CI by default, but can be configured to push to another registry e.g docker hub.

.gitlab-ci.yml

@@ -0,0 +1,38 @@
+image: docker:19.03.12
+
+variables:
+  # When using dind service, we need to instruct docker to talk with
+  # the daemon started inside of the service. The daemon is available
+  # with a network connection instead of the default
+  # /var/run/docker.sock socket. Docker 19.03 does this automatically
+  # by setting the DOCKER_HOST in
+  # https://github.com/docker-library/docker/blob/d45051476babc297257df490d22cbd806f1b11e4/19.03/docker-entrypoint.sh#L23-L29
+  #
+  # The 'docker' hostname is the alias of the service container as described at
+  # https://docs.gitlab.com/ee/ci/docker/using_docker_images.html#accessing-the-services.
+  #
+  # Specify to Docker where to create the certificates, Docker will
+  # create them automatically on boot, and will create
+  # `/certs/client` that will be shared between the service and job
+  # container, thanks to volume mount from config.toml
+  DOCKER_TLS_CERTDIR: "/certs"
+  # Use TLS https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#tls-enabled
+  DOCKER_HOST: tcp://docker:2376
+
+services:
+  - docker:19.03.12-dind
+
+
+before_script:
+  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+
+build:
+  stage: build
+  script:
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG --tag $CI_REGISTRY_IMAGE:latest .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+    - docker push $CI_REGISTRY_IMAGE:latest
+
+  only:
+    - tags