OpenStack Compute supports many hypervisors, an array of which must provide a bit of difficulty in selecting a hypervisor unless you are already familiar with one. You cannot configure more than one virtualization type on the compute nodes, so the hypervisor selection is for the entire installation. These links provide additional information for choosing a hypervisor. Refer to http://wiki.openstack.org/HypervisorSupportMatrix for a detailed list of features and support across the hypervisors.
Here is a list of the supported hypervisors with links to a relevant web site for configuration and use:
KVM - Kernel-based Virtual Machine. The virtual disk formats that it supports it inherits from QEMU since it uses a modified QEMU program to launch the virtual machine. The supported formats include raw images, the qcow2, and VMware formats.
LXC - Linux Containers (through libvirt), use to run Linux-based virtual machines.
QEMU - Quick EMUlator, generally only used for development purposes.
UML - User Mode Linux, generally only used for development purposes.
VMWare ESX/ESXi 4.1 update 1, runs VMWare-based Linux and Windows images through a connection with the ESX server.
Xen - XenServer, Xen Cloud Platform (XCP), use to run Linux or Windows virtual machines. You must install the nova-compute service in a para-virtualized VM.
