Active-Active imap replication separated by wan, no shared storage with ispconfig

There have been various attempts to set up a highly available IMAP system using a wide variety of solutions without much verified success. Dovecot provides a solution for this (dsync) but appears to be theoretical. Dovecot mailing lists have reports of difficulty without much in the way of solutions.

Curious if anyone here has any comments about doing this and if ispconfig has anything to offer. We've run ispconfig multi server setups in the past successfully but primarily for web server, not mail. Also, synchronization of data between the servers had to be done by rsync or something similar. One determined fellow apparently put a great deal of effort into this and ended up with a solution involving syncthing somehow.
Would be interested in any comments or ideas as far as achieving a highly available imap system where the member servers are geographically distant and connected by WAN.

Much appreciated.

 

Thanks very much Thom, this is great to see! May I ask how many accounts have you had success with this setup keeping in sync? And is this a fairly busy setup?
Do you use or recommend a VPN between the two mail servers or is some form of ssh tunneling employed?
Should one server become unavailable is the idea to manually make a dns entry change in order for the imap clients to connect to the other server or is there some other more elegant method with this setup?
Also, after a mail server comes back online after an outage have you found this setup to reliably bring that server up to date or is some sort of administrator intervention needed?

Much appreciated.

 

Thanks for your collaboration, Thom, I very much appreciate it.
Would you mine sharing how many users and # of messages per day you've run on such a setup stably?
My concern is the long-term viability and scalability of such a setup.

The determined fellow I mentioned earlier who has written about this you can see here:
https://www.reddit.com/r/linuxadmin/comments/egzdik/dovecot_multi_master_cluster/
(see fragtionza) comments from 2 yrs ago

It appears this same person posted about his solution here as well:
https://github.com/fragtion/dovecot-core/issues/27
(see fragtion's comment on Jun 24 2020 & TCB13 reply the same day)

My concern is this (and others) reporting instability and CPU spikes and performance issues about 50 users for example.

Regarding the load balancer, while this makes sense, this makes the load balancer the single point of failure. I would be interested in strategies providing a no-SPOF solution.

Thanks again.

 

Good to know on the number of users, we will give it a go.
May I ask what highly available load balancer you've found to be a good fit for this and whether outsourced or using the public cloud, etc?

Thanks

 

another alternative to using load balancers, is to provide both mail servers public ip's for eg imap.domain.tld dns A records.
and let dns responses effectively round-robin the provided ip.
may be an issue with session info, windows clients may be fine, should just keep connecting to the same ip for quite a while, due to dns caching, linux / mac may be more of an issue. replicated redis servers for session data would resolve that, but again, the increased complexity / hassle is probably more effort that it's worth.