Re: [Xen-users] Failover

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

Yep, Chris's comments are a good guide - just pretend the Xen virtual machines 
are real machines.

Just to note: there are some people (in Cambridge and elsewhere) working on 
things like running two *virtual* machines on differenct hosts exactly 
in-step (at the instruction level) to guard against higher-level failures 
without needing application-level fail-over software.  There's no code 
available yet though.

Cheers,
Mark

On Sunday 14 August 2005 23:05, Chris de Vidal wrote:
> --- Matthijs ter Woord <matthijsterwoord@xxxxxxxxx> wrote:
> > Is it possible to eliminate the possibility of a Xen host failure due to
> > hardware failure (ie. failover clustering)?
>
> I'm no Xen expert but from what I can tell you can't to high-availability
> with the Xen kernel itself.
>
> However, if you think about it, there is very little difference between
> domU virtual machines and real machines.  You can easily do
> high-availability on domU guests between two physical Xen hosts.  Run all
> of your services on domUs and use something like UltraMonkey, regular LVS,
> Heartbeat, OpenSSI (assuming it works with the domU kernel patches), or
> some other HA solution giving you failover clustering.
>
> The difference between this and a real cluster is only that Xen is running
> below the virtual machines; very little is different.  They only add a thin
> layer of separation.
>
>
> So for example if your poison of choice is Heartbeat and you want to make
> Apache highly available, you do this:
> Apache1         Apache2
>
>   +---Heartbeat---+
>
> DomU1           DomU2
> virtual         virtual
> machine         machine
>
> Xen1            Xen2
> kernel          kernel
>
> Node1           Node2
> hardware        hardware
>
> A real cluster would look like this:
> Apache1         Apache2
>
>   +---Heartbeat---+
>
> Node1           Node2
> hardware        hardware
>
>
> Very little difference.
>
> Hope that helps!
>
> CD
>
> You have to face a Holy God on Judgment Day. He sees lust as adultery
> (Matt. 5:28) and hatred as murder (1 John 3:15). Will you be guilty?
>
> Jesus took your punishment on the cross, and rose again defeating death, to
> save you from Hell. Repent (Luke 13:5) and trust in Him today.
>
> NeedGod.com
>
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