Recently VMware released Identity Manager 2.7 and with it there is a new requirement when clustering the Identity Manager behind a load balancer.
It is now required that you have a minimum of 3 Identity Manager Appliances with in the cluster.
The diagram below shows this minimum requirement.
This will also help when upgrading to future version. If there is a minimum of 3 appliances then it will be possible to upgrade these appliances one at a time with out any downtime.
To upgrade with a minimum of 3 in the cluster you and simply take a single appliance out of the load balanced pool upgrade the server and then add it back to the load balanced pool. Simply do this for each appliance in the load balanced pool and not down time will be required.