[horde] multiple horde servers?

Jeff Warnica jeffw at chebucto.ns.ca
Wed May 19 09:35:47 PDT 2004

Perhaps you should first ask how to do want to do, rather then how to do
a particular action.

If what you want to do is web server load balancing, doing that in the
web app logic would be, well insane. What I think you want is a "layer
4" switch - and that is not at all related to the web app. Going on that

There are a few commercially available "layer 4" switches, but they are
expensive. What I would recommend (and what I have personally used) is
Linux Virtual Server http://www.linuxvirtualserver.org. While the (using
their terminology) "director" needs to be running Linux, in NAT mode,
the "real servers" could be running any OS. 

In NAT mode, P-200 is more then capable of saturating a 10meg network,
handling up to 15 real servers. There are other modes, which can scale
up better, but are more complex, and may have different "real server" OS
requirements. With persistence, all connections from a given client will
hit the same real server, so sessions can remain file/core based. The
real servers can be blissfully unaware that they are in a cluster.
Scheduling is based on a few options, RR, least connections, and
weighted versions if the real servers have different specs. There is a
related set of tools that allow easily building high availability into
the cluster, detecting when real servers are down, and director fallover
and what not.

I have no idea how well MySQL clustering works. Database servers are one
of the few things that can be easily scaled with clustering.

On Wed, 2004-19-05 at 12:07 +0800, Adrian Chadd wrote:
> Hi,
> I'm rapidly approaching the point where a single server running
> horde/IMP for our Campus Webmail isn't feasable.
> I'd like to look at building a group of webmail servers and
> 'redirect' people to a webmail server, at login, based on
> some metric (round-robin, lowest loadav, lowest usercount, etc.)
> Has anyone done this before? Specifically, will I have any problems
> if I implement multiple horde servers with a shared mysql DB backend
> for the preferences/vfs storage?

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