Hello,
the dispatcher module (kind of fast load balancing support) has now support for failover. Along with selected destination, the rest of addresses in the destination set are stored in AVP list. If the selected destination fails to manage the request, then the next address can be used from failure_route.
Some destinations can be dynamically marked as inactive (e.g., based on reply code) so the are not going to be used until the admin enables them again, via fifo command.
For more info, please see the readme file: http://openser.org/docs/modules/1.1.x/dispatcher.html
Cheers, Daniel