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Re: [libvirt-users] Can a VM tell what host it's on?

On Thu, Feb 2, 2012 at 2:08 PM, Eric Blake <eblake 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 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 :)

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