Scalability with high density servers and proxies, TCP port limits

[Christian Balzer]

On Fri, 3 Jul 2015 14:29:55 +0900 Christian Balzer wrote:

> 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.
> > >
> > 
To follow up on myself, with multiple IPs and appropriate(*) iproute rules
this works as well.

(*) for each IP in "interfaces" add something like this:
---
        up ip route add 192.168.1.0/24 dev eth0 src 192.168.1.109 table T2
        up ip route add default via 192.168.1.1 table T2
        up ip rule add from 192.168.1.109 table T2
---
And the tables in "/etc/iproute/rt_tables".

Christian

> > 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/