Kris Deugau:
> We found that DNS-based round-robin strategies didn't actually balance
> the load very well.
This looks like the same problem that was found (and solved) with
Postfix outbound connection caching; if a destination host became
slow for whatever reason, it became a fatal attractor for connections.
For example, twice as slow -> twice as many clients.
With outbound connection caching, this was solved in the Postfix
SMTP client, by limiting the total duration of an SMTP session.
For example, twice as slow -> half the number of sessions
With inbound SMTP, it is not possible to tell clients to go somewhere
else except by interposition, for example with an layer-3 proxy
(nginx), with a layer 2 switch/nat/etc, or by interposing at the
DNS level (adjust DNS replies according to server load). I don't
know if the last is in use for SMTP.
Wietse
