The hypervisor is the heart of your OpenStack compute node. This is called the virtual machine monitor (VMM), which provides a set of manageability functions for virtual machines to access the hardware layer. The amazing part about hypervisors in OpenStack is the wide range of VMMs that it can offer, including KVM, VMware ESXi, QEMU, UML, Xen, Hyper-V, LXC, bare metal, and lately, Docker.
If you already have some experience with one or more of these, it will be better to take a look at how they differ at an architectural level. Currently, the latest OpenStack release at the time of writing this book is Ocata, which has many hypervisor features added or extended. Keep in mind that not all of these support the same features. The Hypervisor Support Matrix (https://wiki.openstack.org/wiki/HypervisorSupportMatrix) is a good reference that can help you to choose what fits your needs.
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