Resolved Roundcube max processes exceeded despite high maximums

[Bitpalast]

On two of our hosts we allow several thousand concurrent connections from the same IP to IMAP service and several thousand concurrent IMAP connections from any IP. Nevertheless, Roundcube webmail seems to fail with (for example):

[01-Nov-2017 15:23:24 +0000]: <jgbr8klf> IMAP Error: Login failed for webmaster@<domain> from 91.3.27.185(X-Real-IP: 91.3.27.185). Empty startup greeting (localhost:143) in /usr/share/psa-roundcube/program/lib/Roundcube/rcube_imap.php on line 193 (POST /?_task=mail&_action=refresh)

and a "Unable to connect to IMAP server" in the Roundcube GUI. Normally this is caused by exceeding the maximum number of concurrent connections to the IMAP service or the number of concurrent connections from a single IP to IMAP (dovecot). In the cases we are observing these maximums have been set so high that there is no way that they can be exceeded by customer logins, and the log files and process list neither show a high number. Nevertheless, connections fail.

What other parameters on the system could be responsible and limit the number of connections to Dovecot (IMAP service)?

 

[mr-wolf]

Quick Google gave me this:

Unable to login via IMAP: Connection to storage server failed: process_limit (100) reached

 

[Bitpalast]

I must have been blind. I knew the article, but thought: Well, in the configuration files the process_limit is already set.

I did not see however that there is a difference between the imap process limit (which is set by Plesk) and the imap-login process limit (which is omitted by Plesk, and which is the bug). Thank you for pointing me to this article again. I have applied the change and we will now monitor whether it solves the issue.

 

[Bitpalast]

The solution is correct. Thank you again.