dovecot - Oct 2022 - The end of Dovecot Director?

On 2022-10-21 06:19, Zhang Huangbin wrote:
>> On Oct 21, 2022, at 4:19 AM, Antonio Leding <tech at leding.net>
wrote:
>> 
>> My understanding is that Director is targeted toward large enterprise 
>> mail installations that will incorporate several servers for a given 
>> function. In such an environment, Director would be the 
>> fore-person\traffic-cop keeping things organized & squared-away.
> 
> Director is used when you setup frontend servers in a load-balance 
> cluster, proxy imap/pop3/lmtp/managesieve requests to backend Dovecot 
> servers.
> 
> I setup load-balance cluster for clients with HAProxy + KeepAlived + 
> Dovecot Director running in frontend servers, so sad we have to find an 
> alternative to replace Director in such case.
> 
> It's not about "small/medium" servers, but the demand of
imap/pop3/lmtp
> proxy service, especially in load-balance cluster.
> 
> ----
> Zhang Huangbin, founder of:
> - iRedMail: Open source email server solution: 
> https://www.iredmail.org/
> - Spider: Lightweight, on-premises Email Archiving Software: 
> https://spiderd.io
Hi,

I was wondering if one can achieve the same implementation with haproxy 
without dovecot director? Load balancing all requests to pop3, imap, 
managesieve and lmtp services from specified frontend servers i.e. 
webmail to specified backend servers and using NFS mount 
filesystem/syncing data across all servers to access emails with high 
availability?

Not sure whats the big deal director is offering? Is it just a native 
functionality providing a feature to find which backend server have X 
emails available and chooses to load from e.g. its content i.e. like 
checks which first server that doesnt return http 404 response 
equivalent in IMAP/POP3/LMTP/ManageSieve?

Sometime ago I used Varnish caching directors to implement high 
availability using 404 response status in http web server, and it seems 
great if we can have this feature in dovecot too, as it offers high 
availability with delayed-syncing/partial-syncing across unknown 
selected servers, I managed to use Varnish too in dovecot proxy service 
i.e. the webmail, yet it requires NFS mount or high available file 
system all servers can have through immediate access to e.g. maildir?

Any helpful input that would clear the picture for me in regards dovecot 
director, would be ver much appreciated.

With thanks.

Zakaria.

> On Oct 21, 2022, at 5:23 PM, hi at zakaria.website wrote:
> 
> I was wondering if one can achieve the same implementation with haproxy
without dovecot director?
The most important part of Director is it makes sure same mail user always
proxied to same backend IMAP server.

If mailbox is in Maildir format (and stored on shared storage like NFS),
accessing it from different server may corrupt Dovecot index files and mailbox
becomes unaccessible. Director perfectly avoids this issue.

HAProxy can proxy mail user from same client IP to same backend IMAP server, but
not same mail user from different IPs.

Quote (https://doc.dovecot.org/admin_manual/director/dovecotdirector/):

"Director can be used by Dovecot?s IMAP/POP3/LMTP proxy to keep a temporary
user -> mail server mapping. As long as user has simultaneous connections,
the user is always redirected to the same server. Each proxy server is running
its own director process, and the directors are communicating the state to each
others. Directors are mainly useful for setups where all of the mail storage is
seen by all servers, such as with NFS or a cluster filesystem."

----
Zhang Huangbin, founder of:
- iRedMail: Open source email server solution: https://www.iredmail.org/
- Spider: Lightweight, on-premises Email Archiving Software: https://spiderd.io