Re: [Exim] OT: E-mail Redundant Systems

On Mon, 2004-01-05 at 11:37, Odhiambo G. Washington wrote:
> My New Year resolution is to establish a system that will support both
> redundancy and high availability. This will only involve two boxes
> running Exim on FreeBSD platform. The users will be in a MySQL db but I
> also have file-based lookups.

okay, but then the MySQL db becomes the single point of failure, and it
is also hard to keep the files in absolute sync across Exim servers.
the latter may not be a big problem, depending on your configuration,
but you need to consider what happens when they're out of sync -- can
e-mail messages loop?

we're using LDAP generated from a database as our backend for _all_
configuration data. replicating an LDAP service is a well-known
problem, and many organizations need that anyway for other services.


the other problem is the storage. you don't say if you want to do
active-passive or active-active failover. with active-active you need a
storage system which allows simultaneous delivery from more then one
host.

in our old system, we used NFS for this (a NetApp), but this does not
scale very well. in our new system, we're using 12 virtual Cyrus
instances in HP ServiceGuard running on three physical servers, hooked
up to a RAID system via Fibre Channel. each Cyrus instance has a LUN on
the RAID containing all data associated with it. we use Perdition
IMAP/POP proxy software in front of these (with active-active failover
courtesy of LVS) to make them look like one server to our users. Cyrus
Murder may be just as good or better. but this is likely much more
hardware than you need.

--
Kjetil T.