libvirt users - Feb 2012 - Can a VM tell what host it's on?

Is there a way internal to a KVM VM to know which host it's running on? 

It could send a command via ssh to virsh on a host, and learn from that
whether the host currently has it running. But is there something within the
VM itself which will reveal this? 

Thanks,
Whit

On 02/02/2012 01:33 PM, Whit Blauvelt wrote:
> Is there a way internal to a KVM VM to know which host it's running on?
>
> It could send a command via ssh to virsh on a host, and learn from that
> whether the host currently has it running. But is there something within
the
> VM itself which will reveal this?
>
> Thanks,
> Whit

I was under the impression that without some creative uses of DMI, this 
could not be done.

-- bk

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.
> 
> It could send a command via ssh to virsh on a host, and learn from that
> whether the host currently has it running. But is there something within
the
> VM itself which will reveal this? 
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.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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