Add Clustering chapter

docs/ch14-clustering.rst

@@ -0,0 +1,28 @@
+Clustering
+==========
+
+VyOS supports multicast and unicast clustering. Multicast is default and to
+use the unicast method you can add the peer directive to the interface with
+the ip of the other cluster member.
+
+In the example below SSH is clustered between two nodes with the unicast
+method.
+
+.. code-block:: sh
+
+  cluster {
+      dead-interval 20000
+      group cluster {
+          auto-failback false
+          primary vyos
+          secondary vyos2
+          service ssh
+          service 192.168.0.123/24/eth0
+      }
+      interface eth0 {
+          peer 192.168.0.121
+      }
+      keepalive-interval 5000
+      monitor-dead-interval 20000
+      pre-shared-secret S3cr#t
+  }

docs/index.rst

@@ -45,6 +45,8 @@ as a router and firewall platform for cloud deployments.
 
 .. include:: ch13-ipv6.rst
 
+.. include:: ch14-clustering.rst
+
 Indices and tables
 ==================