Add documentation how to enable maintenance mode

SUMMARY.md

@@ -28,6 +28,7 @@
     * [HTTPS](deployment/digital-ocean/https/README.md)
   * [Human Connection](deployment/human-connection/README.md)
     * [Mailserver](deployment/human-connection/mailserver/README.md)
+    * [Maintenance](deployment/human-connection/maintenance/README.md)
   * [Volumes](deployment/volumes/README.md)
     * [Neo4J Offline-Backups](deployment/volumes/neo4j-offline-backup/README.md)
     * [Volume Snapshots](deployment/volumes/volume-snapshots/README.md)

deployment/human-connection/maintenance/README.md

@@ -0,0 +1,43 @@
+# Maintenance mode
+
+> Despite our best efforts, systems sometimes require downtime for a variety of reasons. 
+
+Quote from [here](https://www.nrmitchi.com/2017/11/easy-maintenance-mode-in-kubernetes/)
+
+We use our maintenance mode for manual database backup and restore. Also we
+bring the database into maintenance mode for manual database migrations.
+
+## Deploy the service
+
+We prepared sample configuration, so you can simply run:
+```sh
+# in folder deployment/
+kubectl apply -f human-connection/maintenance
+```
+
+This will fire up a maintenance service.
+
+## Bring application into maintenance mode
+
+Now if you want to have a controlled downtime and you want to bring your
+application into maintenance mode, you can edit your global ingress server.
+
+E.g. in file `deployment/digital-ocean/https/ingress.yaml` change the following:
+```yaml
+...
+
+  - host: nitro-staging.human-connection.org
+    http:
+      paths:
+      - path: /
+        backend:
+          # serviceName: nitro-web
+          serviceName: maintenance
+          # servicePort: 3000
+          servicePort: 80
+```
+
+Then run ` kubectl apply -f deployment/digital-ocean/https/ingress.yaml`. If you
+want to deactivate the maintenance server, just undo the edit and apply the
+configuration again.
+

deployment/volumes/neo4j-offline-backup/README.md

@@ -23,11 +23,7 @@ So, all we have to do is edit the kubernetes deployment of our Neo4J database
 and set a custom `command` every time we have to carry out tasks like backup,
 restore, seed etc.
 
-{% hint style="info" %}
-TODO: implement maintenance mode
-{% endhint %}
-
-First bring the application into maintenance mode to ensure there are no
+First bring the application into [maintenance mode](https://github.com/Human-Connection/Human-Connection/blob/master/deployment/human-connection/maintenance/README.md) to ensure there are no
 database connections left and nobody can access the application.
 
 Run the following: