add overlay vars (1)

.gitlab-ci.yml

@@ -106,17 +106,34 @@ build:pages:
 
 check:links:
    stage: check
-   image: docker
+   image: docker:19.03.0
    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:19.03.1 does this automatically
+     # by setting the DOCKER_HOST in
+     # https://github.com/docker-library/docker/blob/d45051476babc297257df490d22cbd806f1b11e4/19.03.1/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.
+     #
+     # Note that if you're using the Kubernetes executor, the variable
+     # should be set to tcp://localhost:2376/ because of how the
+     # Kubernetes executor connects services to the job container
+     #DOCKER_HOST: tcp://localhost:2376/
+     #
+     # When using dind, it's wise to use the overlayfs driver for
+     # improved performance.
      DOCKER_DRIVER: overlay2
-     # Create the certificates inside this directory for both the server
-     # and client. The certificates used by the client will be created in
-     # /certs/client so we only need to share this directory with the
-     # volume mount in `config.toml`.
-     DOCKER_TLS_CERTDIR: "/certs"
+     # 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: ""
    services:
-     - name: docker:dind
-       command: ["--registry-mirror", "https://docker-registry.lcsb.uni.lu"]
+     - name: docker:19.03.0-dind
+       command: ["--mtu=1458", "--registry-mirror", "https://docker-registry.lcsb.uni.lu"]
    rules:
      - if: $CI_COMMIT_REF_NAME
      - if: $CI_MERGE_REQUEST_ID