[examples] add an example for pre and post run command.

README.md

@@ -16,7 +16,7 @@ docker service create \
   shizunge/gantry
 ```
 
-Or with docker compose, see the [example](examples/docker-compose.yml).
+Or with docker compose, see the [example](examples/README.md).
 
 You can also run *Gantry* as a script outside the container `source ./src/entrypoint.sh`. *Gantry* is written to work with `busybox ash` as well as `bash`.
 

examples/README.md

@@ -0,0 +1,10 @@
+# Examples
+
+## [cronjob](./cronjob)
+
+Run *gantry* at the specific time.
+
+## [prune-and-watchtower](./prune-and-watchtower)
+
+Run [`docker system prune`](https://docs.docker.com/engine/reference/commandline/system_prune/) and [*watchtower*](https://github.com/containrrr/watchtower) with *gantry*.
+

examples/docker-compose.yml → examples/cronjob/docker-compose.yml

@@ -7,7 +7,8 @@ services:
       - /var/run/docker.sock:/var/run/docker.sock
     environment:
       - "GANTRY_NODE_NAME={{.Node.Hostname}}"
-      - "GANTRY_SERVICES_SELF=${STACK}_gantry"
+      # The gantry service is able to find the name of itself service. Use GANTRY_SERVICES_SELF when you want to set a different value.
+      # - "GANTRY_SERVICES_SELF=${STACK}_gantry"
       - "GANTRY_SLEEP_SECONDS=0"
     deploy:
       replicas: 0

examples/prune-and-watchtower/README.md

@@ -0,0 +1,8 @@
+# prune and watchtower
+
+This example run `docker system prune` and *watchtower* before updating docker swarm services.
+
+* [`docker system prune`](https://docs.docker.com/engine/reference/commandline/system_prune/) removes all unused containers, networks and images.
+* [*watchtower*](https://github.com/containrrr/watchtower) updates standalone docker containers.
+* [*gantry*](https://github.com/shizunge/gantry) updates docker swarm services.
+

examples/prune-and-watchtower/docker-compose.yml

@@ -0,0 +1,53 @@
+version: "3.8"
+
+services:
+  gantry:
+    image: shizunge/gantry
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+    environment:
+      - "GANTRY_NODE_NAME={{.Node.Hostname}}"
+      - "GANTRY_PRE_RUN_CMD=SERVICE_NAME=gantry-prune;
+                            docker service remove $${SERVICE_NAME} 2>/dev/null;
+                            docker service create --mode global-job --name $${SERVICE_NAME}
+                              --mount type=bind,source=/var/run/docker.sock,destination=/var/run/docker.sock
+                              --entrypoint docker
+                              alpinelinux/docker-cli
+                              system prune -f;
+                            docker service logs $${SERVICE_NAME};
+                            docker service remove $${SERVICE_NAME};
+                            SERVICE_NAME=gantry-container;
+                            docker service remove $${SERVICE_NAME} 2>/dev/null;
+                            docker service create --mode global-job --name $${SERVICE_NAME}
+                              --mount type=bind,source=/var/run/docker.sock,destination=/var/run/docker.sock
+                              ghcr.io/containrrr/watchtower
+                              --cleanup=true
+                              --label-enable
+                              --run-once=true
+                              --stop-timeout=60s
+                              --tlsverify=true;
+                            docker service logs $${SERVICE_NAME};
+                            docker service remove $${SERVICE_NAME};
+        "
+      - "GANTRY_POST_RUN_CMD=echo \"This is a post run command.\";"
+      - "GANTRY_SLEEP_SECONDS=0"
+    deploy:
+      replicas: 0
+      placement:
+        constraints:
+          - node.role==manager
+      restart_policy:
+        condition: none
+      labels:
+        - swarm.cronjob.enable=true
+        - swarm.cronjob.schedule=45 23 0 * * *
+        - swarm.cronjob.skip-running=true
+
+  cronjob:
+    image: crazymax/swarm-cronjob:latest
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+    deploy:
+      placement:
+        constraints:
+          - node.role==manager