[libvirt-users] non trivial question

[Eric Blake]

[dropping libvir-list, which is for development issue; yours is more of
a usage issue]

On 12/16/2013 01:32 PM, Vasiliy Tolstov wrote:
> Hi all.
> I have very special task - i have some vps on kvm, that sometimes
> needs external support help (administration). But i can't trust
> external workers and need to known what files are changed.
> 
> As i understand best of all - create backup before work and after.
> After that check it for difference and decide apply this work or not.
> Vps need to run all time. (no downtime for work).

Yes, it is possible to take snapshots of a vm with practically 0
downtime, and once you have an external snapshot, you can probe the
state of the filesystem in that snapshot with no interruption to the vm.

> 
> How can i do that and what tools i need to use? Is that possible?

I suggest taking an external snapshot both before and after the point
where the guest is performing unknown changes (your choice of disk-only
or full snapshot with RAM state as well; but it sounds like disk-only
may be sufficient if you are just comparing disk contents between two
snapshots), then look into the tools provided by libguestfs for
comparing file systems between two snapshots.  But while taking
snapshots is possible with no downtime, you do have to be prepared for
the difficulties of rolling back if you don't like what you found when
comparing two snapshots.  To begin with, libvirt support for reverting
to external snapshots is still incomplete, so you'll end up doing some
things manually (the archives of this list discusses the topic, or ask
more questions as you have them); you also have the inherent issue that
a rollback is hard to distinguish from guest downtime (any rollback to
an earlier point in time is somewhat similar to downtime between the
point of the snapshot and the point where you decided to rollback,
because after the rollback, the guest behaves as if no useful work was
done in that stretch of time).

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

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