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On Wed, 2014-12-31 at 20:56 +0100, Chen CH Ji wrote:
>               Sorry If I didn't understand clearly about it , looks to
> me the hypervisor itself hosts the instances and it should have a IP
> with it (like Linux host KVM instances, Linux is the hypervisor, the
> PC is the host)
>               while the host is physical node and only to be used by
> 'hypervisor' concept ,so I think maybe we don't need ip for the
> 'host' ?  thanks a lot

The hypervisor hosts the VMs, yes, but the component that sits between
the hypervisor and the rest of nova—that is, nova-compute—does not
necessarily reside on the hypervisor.  It is the nova-compute node
(which may be either a VM or a physical host) that is referred to by the
nova term "host".  For KVM, I believe the host is often the same as the
hypervisor, meaning that nova-compute runs directly on the hypervisor…
but this is not necessarily the case for all virt drivers.  For example,
the host for Xen-based installations is often a separate VM on the same
hypervisor, which would have its own distinct IP address.
-- 
Kevin L. Mitchell <kevin.mitchell at rackspace.com>
Rackspace