[Dovecot] Proxying improvements in v2.1.2

[Timo Sirainen]

On 25.2.2012, at 5.54, Timo Sirainen wrote:

> I just committed a couple of features that will make life easier for some types of proxying setups:

Oh, and:

4. Added proxy_always=y passdb field. When used with proxy_maybe=y you can create a setup where the connections are proxied to either

 * when user's host matches locally, director assigns a local backend's host for the connection
 * when user's host doesn't match locally, Dovecot connects to that host

So basically you can have a bunch of Dovecot cluster installations behind different load balancer IPs, and have all of the Dovecot proxies redirect the connection to the proper cluster's load balancer, or if it's for a local cluster then redirect to one of the backends.

5. Currently in v2.2 only, could be backported if needed: Added TTL for the proxy connections, so in case two clusters both think the other one should be handling the connection they won't end up creating thousands of connections to each others until finally failing when login process limits are reached. The hard coded TTL is 5, should be more than enough.