The need for HA software to remap ip's should not be there if the service has been designed in a stateless manner. As soon as a service goes down the balancer

The need for HA software to remap ip's should not be there if the service has been designed in a stateless manner. As soon as a service goes down the balancer should send the next request to the next node. In addition - At the entrance of the cloud(external ip's of the balancer) - I would suggest dnsmadeasy that can do round robin dns along with dns monitoring with a low ttl of 5 minutes that in case of failure can change your A records. So the service should be designed with not having to rely on ip re-assignments.