You need to have a load balancer in front of the cluster. The install instructions at http://support.citrix.com/proddocs/topic/cloudportalbusiness-13/ccpb-install.html gives a configuration example of how to set up Apache as a reverse proxy load balancer.

On each CPBM host, make sure these properties are set to your load balancer:
vmops.mgmt.server.publicHost=localhost
vmops.mgmt.server.publicPort=443
vmops.mgmt.server.publicProtocol=https

And also set these values in the UI configuration to your load balancer:
vmops.public.protocol
vmops.public.host
vmops.public.port

-David