[Users] oVirt-engine and UserPortal "cluster"

I've been scouring through the install notes and the architecture documents but didn't find my answer. Is there a way to "cluster" or replicate the userportal app or is it strictly a single instance? Any thoughts to the scale of a large VDI system with 10,000 desktops and their VMs and how that impacts the ovirt-engine and the user-portal app? I figure it has been discussed, but using the word cluster in a google search of the wiki results in a lot of hits, none of them that I saw that are to do with clustering the server, just the virtual machine nodes. Brian