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Right now, if you use KVM via libvirt (the default case), on the
compute node, nova-compute runs on the host. If you use Xen via
xenapi, nova-compute runs on Dom-U. (I'll ignore Xen via libvirt since
no one really uses it.)

What's the fundamental design decision to make the distinction?
Presumably, it is not *that* hard to run nova-compute in a KVM VM,
since the libvirt control socket works on tcp. I can see updating
iptables rules would be painful but shouldn't we have the same problem
with Xen? Conversely, it's also not impossible to run nova-compute in
Dom-0. I understand running something in a VM is more secure in some
sense than running in Dom0. But shouldn't the same argument apply to
KVM's case as well?

Your input is appreciated. Thanks,

Yun