Scalability with high density servers and proxies, TCP port limits

[Christian Balzer]

On Fri, 03 Jul 2015 07:05:43 +0200 Urban Loesch wrote:

> Hi,
> 
> Am 03.07.2015 um 05:14 schrieb Christian Balzer:
> 
> >
> > 2. Here is where the fun starts.
> > Each IMAP session that gets proxied to the real mailbox server needs a
> > port for the outgoing connection.
> > So to support 2 million sessions we need 40 IP addresses here. Ouch.
> > And from a brief test having multiple IP addresses per server won't
> > help either (Dovecot unsurprisingly picks the main IP when
> > establishing a proxy session to the real mailbox), at least not with
> > just one default GW.
> >
> 
> If I remeber correctly there is a config option in dovecot 2.x where you 
> can set the ip addresses which dovecot should use for outgoing proxy 
> connections. Sorry, but I can't remeber the option.
> 
Looking at the documentation on the Wiki I was going to say "That won't
help", as it says address.
http://wiki2.dovecot.org/PasswordDatabase/ExtraFields/Proxy

But since that page is rather terse, I looked up the changelog and found
that it indeed was added for use cases like mine:
http://www.dovecot.org/list/dovecot-cvs/2014-June/024574.html

Unfortunately the latest dovecot version in Debian is 2.2.13...

Additionally this still leaves the actual mailbox servers, which in my
case will need to be able to handle more than 50k sessions as well. 

Thanks for the info,

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Global OnLine Japan/Fusion Communications
http://www.gol.com/