Imap connections
Running out of imapd connections
The problem looks like this from xymon:
yellow Wed Feb 6 11:02:18 2013 imap NOT ok Service imap on localhost is not OK : Unexpected service response Seconds: 0.000132
And clients see intermittent errors trying to connect.
And syslog shows this:
Feb 6 11:18:20 weasel imapd: 40 maximum active connections. Feb 6 11:18:20 weasel imapd: Maximum connection limit reached for ::ffff:10.0.0.66 Feb 6 11:18:23 weasel imapd: last message repeated 3 times Feb 6 11:18:28 weasel imapd: Maximum connection limit reached for ::ffff:10.0.0.66 Feb 6 11:18:28 weasel imapd: Maximum connection limit reached for ::ffff:10.0.0.66
This shows which clients are holding onto connections:
root@weasel:/etc/init.d# netstat -n |grep :143 | sort -k +4
Count which ones are in the ESTABLISHED state:
netstat -n |grep :143 | grep ESTAB | sort -k +4 | wc
or
lsof -i :143 | wc
When my phone is connecting through the telco network instead of wifi, the connection looks like this:
Verizon (myvzw.com)
tcp6 0 242 216.99.216.99:143 70.199.228.147:11752 ESTABLISHED
T-Mobile (tmodns.net)
tcp6 0 0 216.99.216.99:143 208.54.32.249:64691 ESTABLISHED
This shows the processes:
root@weasel:/etc/init.d# ps -eaf | grep imapd | wc
39 397 3487
Why?
I know we have a lot of devices laying around. But what changed? Did the clients change or did the server change?
Raise the limits
http://kb.mediatemple.net/questions/259/How+can+I+raise+Courier-IMAP+connections+for+my+server%3F
Immediately after raising the limit and restarting imap, I had 13 active connections, all in the established state. A nexus tablet had the most connections open, 4. The other clients had one or two.
root@weasel:/etc/courier# grep MAX imapd ##NAME: MAXDAEMONS:0 MAXDAEMONS=80 ##NAME: MAXPERIP:0 MAXPERIP=40