From dovecot director point of view it does not make any difference if your imap clusters have only one server each. mail_hosts takes IP addresses, DNS names whatever, and you can assign tag per host if you want.
And yes, if you have only one server for a tag, then your clients are denied access.
Aki
On 31/08/2021 12:28 Steven Varco <dovecot.org@bbs.varco.ch> wrote:
Hi Aki
Thanks for pointing out the tag feature which sound really interesting in the first place.
However, if I understand the documentation correctly:
With tags you can use a single director ring to serve multiple backend clusters. Each backend cluster is assigned a tag name, which can be anything you want. By default everything has an empty tag. A passdb lookup can return "director_tag" field containing the wanted tag name. If there aren't any backend servers with the wanted tag, it's treated the same as if there aren't any backend servers available (= wait for 30 secs for a backend and then return temporary failure).
As of my understanding, this only helps if there are multiple IMAP _clusters_ in the doveadm ring. In my case I have only one cluster (with two IMAP _servers_) and would want to go to a specific server, failing over to another if that is unavailable. Now if I have the following scenario:
# Director Server (DEV) root@lb01 [~] # doveadm director status mail server ip tag vhosts state state changed users mx01.example.com mx01 100 up - 0 mx02.example.com mx02 100 up - 1
# IMAP Server (DEV) root@mx01 [~] # doveadm user 'test@example.com' field value uid 1025 gid 12 home /srv/mail/example.com/test mail maildir:~/Maildir maildir example.com/test/ mail_home /srv/mail/example.com/test quota_rule *:storage=20480 sieve_dir /srv/mail/example.com/test/sieve director_tag mx01
Than user 'test@example.com‘ would go to the backend host mx01.example.com, BUT, if mx01.example.com goes down, it would probably fail, because user 'test@example.com‘ wants tag „mx01“, which is now down and the only server with that tag?
By the way, I did a quick live test and it does not even seem to work, when both hosts are up, failing with the log entry on the dovecot server: Aug 31 11:11:11 lb01 dovecot: director: Error: director: User test@example.com host lookup failed: Timeout because no hosts - queued for 30 secs (Ring synced for 385 secs, hash=1561836376)
Do see what I’m missing out here? Using dovecot 2.2.36 (1f10bfa63) on both the directror and IMAP backend.
thanks, Steven
Am 30.08.2021 um 19:20 schrieb Aki Tuomi <aki.tuomi@open-xchange.com>:
On 30/08/2021 19:09 Steven Varco <dovecot.org@bbs.varco.ch> wrote:
Hi All
I have a dovecot cluster with directror and two IMAP Servers behind.
Since they are in geographical different locations I would like to have users to go to a specific IMAP backend server (if both are up) and only switch to the other if one goes down (failover).
As to my current knowledge the PassDB extra field „host=„ is not suitable in this case as it would never route the client to a different backend, even if the „user specific backend“ would be down.
Is their a way in dovecot to achive this? As far as I searched the documentation I could not find any information on this so far.
If not, it may also help if I could get certain users to „initially" go to a specific backend (since director usually routes a client/user to the same backend server it initially connects) and therefore it would be interesting to know how dovecot director chooses wether a user goes to server1 or server2? And if a client already gets to server2, how to bring it „back“ to server1?
thanks in advance, Steven
Hi!
Use dovecot director tag feature. You can match users with tag= to a specific backend@tag.
Aki