That's a nice suggestion. Thanks John.
On Fri, Jul 12, 2024 at 11:25 PM John Fawcett via dovecot dovecot@dovecot.org wrote:
On 12/07/2024 13:05, Jeff Pang via dovecot wrote:
Hello,
Does the community version of dovecot have the replication feature? When one dovecot was down, another one could take over the tasks.
Thanks.
Jeff
Replication is in the current dovecot version but will go away in 2.4.
The doveadm sync feature is staying. So with some work you can set it up what you are requesting.
I used to use replication and now I'm thinking about using sync but have not implemented it. The following are thoughs on it.
There are some points to be addressed that are outside dovecot. I think you'd have to make sure that your sync happened frequently enough that you could live with losing the emails that arrives bewteen syncs for example. That would tend to lead to a requirement to sync more frequently and reduce risk of email loss. But then you'd need to avoid more than one sync being active simultaneously (that is my assumption that this would not work, but I don't know if it is a real problem).
The failover would require you to stop people accessing the old server, stop syncing and start the backup instance. When the main instance is available to come back on line, you'd need to stop the backup instance, sync in the opposite direction and then start dovecot and re-enable the sync mechansim towards the backup.
You need to ensure people don't connect simultaneously to both instances. So some thought would be needed about those cases where the main node goes and then comes backup to ensure that your sync is not still active at that point and replicates the old state onto the backup server and to ensure then people don't start connecting to it again without being able to control it.
It's a disaster recover rather than high availability solution, but I think it can work. Others may already have got working implementations and thought through some of the implications.
John
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