Add note about checking if all the hostnames are resolvable

Change-Id: I6c353a02a86cd76b2a2e7bd67801a95dd2b04d4f
Closes-Bug: #1559809

doc/source/user/multinode.rst

@@ -207,6 +207,12 @@ to them:
 
     kolla-ansible prechecks -i <path/to/multinode/inventory/file>
 
+.. note::
+
+   RabbitMQ doesn’t work with IP addresses, hence the IP address of
+   ``api_interface`` should be resolvable by hostnames to make sure that all
+   RabbitMQ Cluster hosts can resolve each others hostnames beforehand.
+
 Run the deployment:
 
 ::