The default connection limit values of dovecot are pathetic - unless you run a home mail server where there is only you, the cat and the dog using it.
OP, lots of editing with trial and error required. from memory massive increases needed to: service auth -> client limit service imap-login -> process limit service imap -> process limit if using pop3, repeat above two steps s/imap/pop3/ service managesieve -> process limit service anvil -> client_limit (and system ulimit) I'm on holidays in australia at moment so don't have access to copy and show you a working example for 4K users, i will be back on hong kong in 17 days until then i have very limited access. On 2/4/15, Jiri Bourek <bou...@thinline.cz> wrote: > On 02/03/2015 03:35 PM, Ron Cleven wrote: >> We are gradually rolling out Dovecot (IMAP only, no POP3) to our >> customer base. We are replicating between a pair of CentOS 7 boxes. All >> has been working wonderfully. However, to be sure our rollout continues >> to go smoothly, we put together a simple benchmark client program to >> fire up X persistent IMAP connections (using hundreds of mailboxes) that >> login, list the folders, select the INBOX, periodically FETCH an email >> from the INBOX, and otherwise sit in an IDLE loop. As long as we keep >> the number of concurrent IMAP connections under 2k, everything works >> fine. 2,000 processes generate a minimal load on the server. However, >> 2048 is a "hard limit" for number of IMAP processes on a box the way >> things are configured right now. The number (2048) is a bit too magical >> to be anything but a misconfiguration of either some kernel limit or a >> dovecot configuration limit. I have been unable to figure out where >> else to look. I have pasted in my dovecot config below along with the >> kernel setting for max_user_instances. >> >> Hoping someone can tell me what stupid mistake I have made or what else >> to check. >> >> Just an aside, we front-end this with a separate set of proxy servers >> that provide an SSL front-end, hence, no SSL in the dovecot config. >> > > You didn't mention but did you try checking process_limit and > client_limit for various Dovecot services in the output of doveconf | > less ? If I remember correctly, as long as imap process lives, it is a > client of anvil process. When anvil reaches it's maximum, it's no longer > possible to run more imap processes and therefore no longer possible to > connect more clients. > > I think I hit some similar problem in the past, but in my case Dovecot > complained during startup and warned that anvil's client_limit is too > low compared to imap process_limit and that it could lead to problems. > So I just increased the limit and was done with it. > > That said, this was some time ago so process and setting names can be > completely wrong. Hope someone more knowledgeable corrects me in that case >
