On Tue, 2007-11-13 at 12:11 +0000, Andrew Johnson wrote:
> 2 other alternatives :-
>
> Hardware loadbalancer (such as Alteon or F5)
>
> Linux as a loadbalancer - there are various iptables options that can be
> used to loadbalance connections, though I'm not sure how well these work if
> one of your email servers goes down.
...and wearing my list owner hat for the Linux Virtual Server project, I
would like to point everyone towards linuxvirtualserver.org and the
resources contained therein.
Using iptables for load balancing isn't very robust.
Using LVS for load balancing isn't very robust on its' own...
> At least with the Alteon load balancers, they can do helath checks and look
> for smtp banners to decide if the server is available.
...unless you make use of one of the varied approaches to combining load
balancing and health checking - the two most common (it seems) being
keepalived (
http://www.keepalived.org) and ldirectord
(
http://www.vergenet.net/linux/ldirectord/). There's also heartbeat
(which is part of the linux-ha project,
http://linux-ha.org/Heartbeat).
These are all tremendously flexible pieces of software. I have built
several load-balanced HA SMTP/IMAP/POP systems using one or more of
them.
Graeme
