Docker clean.

Run the docker-clean image daily. Remove failed builds and such.

crond/.dockerignore

+*
+!crontab

crond/Dockerfile

+FROM docker:19.03 as docker
+
+# hadolint ignore=DL3006
+FROM adarnimrod/cron as supersonic
+COPY --from=docker /usr/local/bin/docker /usr/local/bin/
+COPY --chown=root:root crontab /crontab
+# hadolint ignore=DL3002
+USER root

crond/README.md

+# crond
+
+> Cron container image.
+
+## Description
+
+This container periodically runs the [docker-clean
+image](https://hub.docker.com/r/adarnimrod/docker-clean). For this the `dockerd`
+socket is bind mounted to this container.
+
+## License
+
+This software is licensed under the MIT license (see `LICENSE.txt`).
+
+## Author Information
+
+Nimrod Adar, [contact me](mailto:nimrod@shore.co.il) or visit my [website](
+https://www.shore.co.il/). Patches are welcome via [`git send-email`](
+http://git-scm.com/book/en/v2/Git-Commands-Email). The repository is located
+at: <https://git.shore.co.il/nimrod/>.

crond/crontab

+@daily docker run --rm --name=docker-clean --volume /var/run/docker.sock:/var/run/docker.sock adarnimrod/docker-clean

docker-compose.yml

@@ -15,6 +15,11 @@ services:
     volumes:
       - config:/etc/gitlab-runner
       - /var/run/docker.sock:/var/run/docker.sock
+  crond:
+    build:
+      context: crond/
+    volumes:
+      - /run/docker.sock:/run/docker.sock
 
 volumes:
   config: