Clustering and HA are different things on HornetQ.
Backup nodes are configured as noted on chapter 39 : http://hornetq.sourceforge.net/docs/hornetq-2.1.1.Final/user-manual/en/html/ha.html
Discovery is used on clustering, not on backup nodes.
I was missing the attribute "backup-connector-name". So to configure the broadcast group with live/backup pair, the broadcast configuration has to look something like this:<broadcast-groups><broadcast-group name="bg-group1"><group-address>18.104.22.168</group-address><group-port>9876</group-port><broadcast-period>5000</broadcast-period><connector-ref connector-name="netty" backup-connector-name="backup"/></broadcast-group></broadcast-groups>
With that change, the live server broadcast it's backup, and automatic client failover works.