To ensure that service clients always connect to an operational node in the cluster, an external load-balancer should be used for automatic failover and/or load distribution.
In the case a custom application is being developed for consumption of the services provided by the Hardware Appliances’ external interfaces, this could also be handled by making the custom application connect to any of the nodes that is found to be operational.
If lower availability and manual interaction is acceptable in case of a node failure, this could also be solved by redirecting a DNS name to the service.