--On 11 July 2007 06:57:20 -0700 Marc Perkel <[EMAIL PROTECTED]> wrote:

>
> I'm using a different failover system. I have a main server on the low
> mx and several backup servers on the next highest mx.
>
> dummy0.junkemailfilter.com - 10 - semi-dead IP
> mx.junkemailfilter.com - 20 - main server
> mx.junkemailfilter.net - 30 - multiple backup servers
> mx.junkemailfilter.org - 40 - several IP where I log connect attempts
> dummy1.junkemailfilter.com - 50 - several IP where I log connect attempts
>

Hmm, that's just a case of having backup servers. Works fine for ordinary 
SMTP, but isn't good enough for MUAs. When we set up our cluster, we set up 
the 4 machines on a round-robin DNS, so smtp.sussex.ac.uk points to four IP 
addresses. That seems to work well with MTAs, but doesn't work at all with 
MUAs.

In order to provide high availability message submission, all four IP 
addresses have to be available at the same time. That's why we introduced 
IP failover. In theory, any one of the four machines could support all four 
SMTP IP addresses at the same time.

We use spread/wackamole for failover, and it works really quite nicely, 
though not perfectly. I'd estimate that downtime is reduced by an order of 
magnitude.

-- 
Ian Eiloart
IT Services, University of Sussex
x3148

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