[Xen-users] Re: Redundant server setup

[Matthew Palmer <mpalmer@xxxxxxxxxxx>]

On Thu, May 11, 2006 at 09:11:48PM -0400, Miles Fidelman wrote:
> Matthew Palmer wrote:
> >On Thu, May 11, 2006 at 11:13:48PM +0200, John wrote:
> >>Hello all,
> >>
> >>I would like your advise/opinion on setting up a redundant Xen
> >>infrastructure. We have two identical boxes now running xen: vs01 and
> >>vs02 - interconnected with a cross cable on eth1.
> >>
> >>What I would like to realize is my virtual hosts not being dependent on
> >>(a) physical hardware and (b) potential Xen failures due to
> >>misconfiration anywhere in the machine. 
> >>
> >>All virtual servers are running on vs01 and I plan to rsync
> >>the whole /etc/xen directory to vs02 every night. I tried using scp and 
> >>that
> >>worked OK. 
> >>
> >>Would this be a good setup to realize redundancy? 
> >
> >Not particularly.
> >
> >What you want is drbd syncing your block devices, with heartbeat 
> >maintaining
> >the "services" of your domUs.  That'll save you from hardware failures, and
> >really nasty Xen misconfigurations (of the "I b0rk3d my grub" severity).  
> >It
> >won't save you from minor stuff-ups, like giving a domU the wrong bridge --
> >but then again, there's not much that will manage to save yourself from
> >yourself like that.
> >
> >To ensure that configurations are properly synced across dom0s, I'd highly
> >recommend a structured configuration management system like Puppet.  The
> >domUs can be managed using the same tool, as well.
>
> I don't suppose anybody's written a HOWTO on this.  I'm looking to do 
> something similar.

Probably not -- it's pretty trivial to do the Xen-specific parts of it.  Use
the DRBD HOWTO to get the DRBD portion of it working, and the heartbeat docs
for the failover.  The only Xen-specific bit is the heartbeat resource file,
which is about 10 lines of shell.

These days I have it all in a config management program and tell the system
"you're a failover dom0 for VM <X>" and the system works it all out for me. 
Now all I have to do is write a small program that gathers customer
requirements, and I can retire to the mountains.  <grin>

- Matt

-- 
Sure, it's possible to write C in an object-oriented way.  But, in practice,
getting an entire team to do that is like telling them to walk along a
straight line painted on the floor, with the lights off.
                -- Tess Snider, slug-chat@xxxxxxxxxxx

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