[#4362] Updated HA section with a note

modified:   doc/sphinx/arm/hooks-ha.rst

diff --git a/doc/sphinx/arm/hooks-ha.rst b/doc/sphinx/arm/hooks-ha.rst
index 3c5e6822936c9cc36cd9dc28eaf3955c061b4361..07b3c225889b8559b028c3cc06f0725def7e0715 100644 (file)
--- a/doc/sphinx/arm/hooks-ha.rst
+++ b/doc/sphinx/arm/hooks-ha.rst
@@ -2463,6 +2463,22 @@ can be any of the peer names in the relationship. For example, if a relationship
 ``server1`` and ``server2``, it does not matter whether the ``ha-server-name`` is ``server1`` or
 ``server2``. In both cases, it associates a subnet with that relationship.
 
+It is important to note that each relationship on a given Kea server must use a unique
+listener IP.port combination as the relationships do not share listener pools between them.
+If the same IP and port are defined for multiple relationships, the Kea service will fail to start with an error something like: DHCP4_INIT_FAIL failed to initialize Kea server: configuration error using file 'kea-dhcp4.conf': Error initializing hooks: CmdHttpListener::run failed: unable to setup TCP acceptor for listening to the incoming HTTP requests: bind: Address already in use
+
+.. note::
+
+    It is important to note that each peer on a given Kea server must use a unique a listener
+    IP/port combination.  If the same IP and port are defined for multiple peers, the Kea service
+    will fail to start with an error similar to the following:
+
+    .. code::
+
+        DHCP4_INIT_FAIL failed to initialize Kea server: configuration error using file 'kea-dhcp4.conf':
+        Error initializing hooks: CmdHttpListener::run failed: unable to setup TCP acceptor for listening
+        to the incoming HTTP requests: bind: Address already in use
+
 It is not required to specify the ``ha-server-name`` in the branch servers, assuming that the
 branch servers only contain the subnets they serve. Consider the following configuration for
 branch ``server3``: