Re: [libvirt-users] Can a VM tell what host it's on?
On Thu, Feb 2, 2012 at 2:08 PM, Eric Blake <eblake(a)redhat.com> wrote:
Did you mean for this to go to the list?
Yes, sorry :)
On 02/02/2012 12:04 PM, Paul Lussier wrote:
> On Thu, Feb 2, 2012 at 1:52 PM, Eric Blake <eblake(a)redhat.com> wrote:
>> On 02/02/2012 11:33 AM, Whit Blauvelt wrote:
>>> Is there a way internal to a KVM VM to know which host it's running on?
>>
>> No. The ideal hypervisor is one where the guest doesn't even know it is
>> running as a virtual machine. And consider live migration - a guest
>> might not be running on the same host over its lifetime. Therefore,
>> there should be nothing that requires a guest to know which host it is
>> running on.
>
> From a system administration perspective, though, it's imperative to
> know what physical hosts your VMs are running on. Perhaps the VM
> itself doesn't know, but the sysadmin should be able to have some
> means of figuring this out in a dynamic manner, not simply by "keeping
> track" of where VMs are deployed.
Yes, but that's a different question. It's not the guests' job to know
which host they are running on, rather, it's the management app _outside
of the guests_ that knows which hosts are running which guests.
What do you mean by "management app", virt-manager, or something else ?
>> Why do you think you need it? Perhaps if you ask a better
question
>> about what you are really trying to solve, we can give a better answer.
>
> Asset tracking, physical host trouble-shooting, etc. If I'm running
> an environment with 2K physical systems, each of which are running 20+
> VMs, and someone reports a problem with vm-23475, it would be really
> nice to know that I can ask that VM where it is on my network and on
> what physical hosts. Especially if that VM has been around a while
> and possibly migrated to/from several physical systems.
That's more a question you should be directing to your management app,
not to your guest. Your management app should know which host is
currently running vm-23475; you shouldn't have to directly query
vm-23475 itself (besides, if you treat guests as untrusted code, you
wouldn't want to rely on any answer vm-23475 gave you in the first place).
While I agree with you in principle, my impression is that people are
not treating guests as untrusted code, but rather, almost exactly like
physical hosts. Perhaps I haven't had the luxury of being in a
virtual environment where people are doing things the way they were
intended :)
--
Paul