I'm trying to understand how the various virtualization vendors (specifically Amazon EC2, but also VMware and Xen) enable software vendors to provide a real HA solution in the environment where the servers are virtualized.

Specifically, if I'm running any HA application (exchange, databases, etc) I need to ensure that my redundant virtual "servers" aren't located on the same physical server.

Using in-house virtualization solutions (VMware, Xen, etc) I can provision accordingly as well as check the virtual -> physical arrangement. I could, however, accidentally "vmotion" to the same physical hardware.

With EC2, I don't even have the ability at provision time to select different physical servers. Since their Cluster Compute Instances are 1 virtual server per physical server it seems to be the only way to guarantee I don't have a false sense of redundancy.

Any ideas or thoughts would be helpful. What are others doing about this problem? If the vendors provided an API where I could get something as simple as a unique physical system identifier I could at least know if I'm going to have an issue.

-Tim