See HA setup guide instructions below. These steps need to be automated, and will be implemented differently given that config.defs is going away per XPB-624.

On both the Master and Distributed Servers, edit the file /etc/sipxpbx/config.defs
Find the setting for:
       REGISTRAR_SERVER_SIP_SRV_OR_HOSTPORT
and set it to:
       REGISTRAR_SERVER_SIP_SRV_OR_HOSTPORT=rr.${MY_FULL_HOSTNAME}
Find the setting for:
       AUTH_PROXY_SERVER_SIP_SRV_OR_HOSTPORT
and set it to:
       AUTH_PROXY_SERVER_SIP_SRV_OR_HOSTPORT=ap.${MY_FULL_HOSTNAME}