On Fri, Aug 14, 2009 at 05:29:12PM +0100, Ian Eiloart wrote: > > Any sort of clustering or load balancing would be done outside of Exim. > > high-availability is "built in" to SMTP by the ability to set multiple > > MX records, and the ability to retry.
Although you would need some 'high availability' mail store that exim could deliver to ... As pointed out below: talking about exim is not quite the same as talking about MS exchange; to get the same thing you would need to add mail storage (or use a MDA) and something like imap/pop so that the MUAs could get mail. If you really are into high availabilty then you perhaps want to choose cyrus over squirrel mail, cyrus will handle the MDA & IMAP serving. Cyrus is much harder to get going than many other IMAP servers. > Which is fine for MX servers. Not so good for MSA. MUAs (user clients) > don't use MX records, and don't retry even if the smtp server address is a > round robin in the DNS. At least, none of the servers that I've tried. No, you prob need an aggegator or IP failover system (heartbeat, etc) to handle that. > We have a cluster of four OSX Server servers with Exim. With three, Apple's > IP failover was just about managable. With four we switched to using > Wackamole on Spread. That works quite nicely, but occasionally a failover > throws up faults with ARP caches, leaving some of the IP addresses > unavailable. > > As a result, we've recently put the MSA servers behind a CoyotePoint > equaliser. We publish a single IP address for MSA, and the equaliser does > load balancing and high availability. It regularly checks to see that it > can get an SMTP greeting from each of the servers - if not, then that > server doesn't get any traffic till its fixed. > > Of course, the equaliser becomes a single point of failure... And so it > goes... > > The equaliser doesn't fail as often as the ARP cache corruptions occur. -- Alain Williams Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer. +44 (0) 787 668 0256 http://www.phcomp.co.uk/ Parliament Hill Computers Ltd. Registration Information: http://www.phcomp.co.uk/contact.php Past chairman of UKUUG: http://www.ukuug.org/ #include <std_disclaimer.h> -- ## List details at http://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
