Author here. Actually it is using double nested virtualization. So there's 4 levels involved: * Amazon runs Xen (bare metal OS) * We run our hypervisor on top

Author here. Actually it is using double nested virtualization. So there's 4 levels involved: * Amazon runs Xen (bare metal OS) * We run our hypervisor on top of Amazon (first level guest) * Customer runs OpenStack compute node (second level guest, first level of nested). * Instance runs on Openstack (third level guest, second level nesting)