Persist runner DIND storage (and do monthly cleanup)

ansible/roles/forgejo_runner/files/docker-compose.yml

@@ -18,6 +18,9 @@ services:
     image: docker:dind
     environment:
       - TZ={{ timezone }}
+      - DOCKER_HOST=tcp://0.0.0.0:2375
+    volumes:
+      - /mnt/ci-runner-docker:/var/lib/docker
     privileged: true
     restart: unless-stopped
     command: dockerd -H tcp://0.0.0.0:2375 --tls=false

ansible/roles/forgejo_runner/tasks/main.yml

@@ -21,3 +21,10 @@
     owner: "{{ docker_user.name }}"
     validate: docker compose -f %s config
   notify: restart forgejo-runner
+
+- name: Clean up runner docker containers
+  cron:
+    name: clean up runner docker containers
+    special_time: monthly
+    job: docker compose -f /opt/forgejo-runner/docker-compose.yml exec dind docker system prune -af --volumes
+    user: "{{ docker_user.name }}"