On Wed, Dec 13, 2006 at 10:50:52AM +0000, Niall O Broin wrote:
> After being a long time fence sitter, I've at last started to use Xen
> and it's every bit as nifty as the many users I've spoken to say it
> is (including some inhabitants of this parish who use it in
> production on some quite big systems).
>> I'm now looking at deploying some production servers using Xen, and
> one major reason for this is the ability to fail over to a Xen
> instance on a different box.
>> In the case in point, failover will not be seamless, as the live and
> standby boxes will be in different data centres, but we have no PI
> space, hence we will be failing over to different IPs. From the POV
> of service consumers, this will be handled by relatively short DNS
> timeouts (while failure of this application is painful, nobody's
> going to die, so the short timeouts method is acceptable).
>> My question now is how to handle this from the POV of the service
> provider, specifically the change of IP. As I see it, we have two
> choices.
>> 1) Manipulate the LVM disk on the standby server after is it has been
> updated to give it the correct IP.
>> 2) Run the domUs in rfc1918 space, and use iptables on the dom0s to
> route packets as needed.
>> 1) has the advantage of simplifying the dom0, whereas 2) has the
> advantage of simplifying the sync process.
>> Opinions? And especially, is there a 3) (or even a 4) ) that hasn't
> occurred to me?
>
If you are planning to use Xen's migration facility ("xm migrate") then
you're likely to be disappointed. Xen only migrates the virtual machines
memory - not it's disk image. The upshot of this is that the two dom0s
that participate in the migration need to be using the same storage (eg,
the same SAN, or possibly NFS). I can't see how you're going to get this
to work if the dom0s are in different data centers.
BTW I'm flying blind here - I've never actually tried Xen migration,
I'm just going by the user guide.
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