Hi,
So we're considering an iMS load-balanced/redundant setup. Mostly because we have
some high-volume mailing lists hosted (lots of POST activity), but also because e-mail
is the most relied-upon service we offer. I wanted to run a couple of my theories
past you all, especially Howie :) Please jump in if any of this sounds off-base. I
could have sworn I read about this somewhere before (specifically re: iMS) but can't
find it now.
1) The actual load-balancing system is somewhat irrelevant to iMS (hardware vs.
software vs. round-robin DNS). In general terms I'm talking about 2 "front-end"
machines that are linked to a common file server.
2) Seems to me that the POST queue needs to be machine-specific (one queue per iMS
instance). Otherwise 2 POST processes might try to send the same mail (?). Also
having the queue on a local disk should speed up processing due to the many .mail file
interactions going on. However, it'd be cool safety-wise to have a shared queue (for
example one server dies... mail gets stuck in its queue). Any way to do this?
3) The local mail repository has to be on a shared disk so that either POP server can
get to it. I would think that having 2 POP servers shouldn't make any difference in
terms of file access/locking, since 1 POP server can have multiple sessions anyway
(including from the same client). Having the mail repository on a network disk
shouldn't affect performance much though it will certainly increase network load a bit.
4) For performance considerations, the SMTP server should use a local drive to spool
the mail files to as they come in, then the DATA template can take care of re-writing
the file to the shared disk (mine does the re-writing already). This is probably a
minor point since copying the file will be part of the delivery process anyway. I
would think the real savings come in only when the mail file doesn't need to be copied
over (fwd. acct, bad mail, rcv. timeout, whatever).
5) Template directory should be local to iMS machine to increase performance/reduce
network traffic (although with CF caching the templates (non-trusted cache) this is
probably only a minor savings).
6) Dedicated Log and Counter folders for each iMS instance would be required. Any way
to merge counter files?
7) Get another iMS license!
Anything else I need to consider (I'm already familiar with load-balancing in general,
having done it with our Web/application servers)? How about other ideas to improve
reliability/throughput of a mail system? Any input or resource pointers are
appreciated.
TIA,
-Max
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