High Availability of a web server on a distributed cloud

[Dave Cramer]

On Mon, Jan 14, 2013 at 9:43 AM, Digimer <lists-5ZoueyuiTZiw5LPnMra/2Q at public.gmane.org> wrote:

> On 01/14/2013 09:33 AM, Jamon Camisso wrote:
> > On 13-01-14 08:57 AM, Dave Cramer wrote:
> >> It is relatively simple to distribute an application to a number of
> servers
> >> and use haproxy to switch ip's. What I can't figure out is how to switch
> >> make sure that the IP that points to ha-proxy can be moved easily if
> that
> >> machine fails ?
> >
> > Research things like pacemaker, heartbeat, stonith, and using 3 or more
> > nodes in your system (3 nodes so that you don't end up in a split brain
> > situation, especially if your systems are distributed).
> >
> > You'll likely want another back-channel method of communicating between
> > each system in case something goes awry - what if one your ISP/cloud
> > providers can't route public traffic to a node, but the node still
> > thinks it is online?
> >
> > You want some method of achieving a quorum between remaining nodes, and
> > some method of killing off the rogue node.
>
> A few points;
>
> - Heartbeat is deprecated, don't use it.
> - Quorum is optional. Both pacemaker and cman/rgmanager (Red Hat) use
> corosync for cluster communication and membership. Both can disable
> quorum and this is fine.
> - The members need to be (physically) close to each so that you can use
> fencing. Fencing is critical to safe operation of a cluster. Without it,
> it is easy/possible for a split-brain to occur.
>
>

If you place your machines physically close to one another then a
geographical outage can take them both out. I guess pacemaker is more for
machines dying than for geographical high availability

Dave
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