Updated multi-region docs to include keepalived

The keepalived_virtual_router_id should be changed from the default in
the case of a multi-region deployment where the VIP of the different
regions resides on the same subnet.

This is not immediately clear - this change should make it more obvious.

Change-Id: Ia4899ba407937d9f27832c9d123701729e89987a

doc/source/user/multi-regions.rst

@@ -79,6 +79,14 @@ the value of ``kolla_internal_fqdn`` in RegionOne:
        project_name: "admin"
        domain_name: "default"
 
+.. note::
+
+   If the ``kolla_internal_vip_address`` and/or the
+   ``kolla_external_vip_address`` reside on the same subnet as
+   ``kolla_internal_fqdn_r1``, you should set the
+   ``keepalived_virtual_router_id`` value in the ``/etc/kolla/globals.yml``
+   to a unique number.
+
 Configuration files of cinder,nova,neutron,glance... have to be updated to
 contact RegionOne's Keystone. Fortunately, Kolla allows you to override all
 configuration files at the same time thanks to the

etc/kolla/globals.yml

@@ -122,6 +122,8 @@
 # keepalived options
 ####################
 # Arbitrary unique number from 0..255
+# This should be changed from the default in the event of a multi-region deployment
+# where the VIPs of different regions reside on a common subnet.
 #keepalived_virtual_router_id: "51"
 
 ###################