Dovecot cluster using GlusterFS

[Filip Pytloun]

Hello,

I have recently setup mailserver solution using 2-node master-master
setup (mainly based on MySQL M-M replication and GlusterFS with 2
replica volume) on Ubuntu 14.04 (Dovecot 2.2.9).

Unfortunately even with shared-storage-aware setting:

 mail_nfs_index = yes
 mail_nfs_storage = yes
 mail_fsync = always
 mmap_disable = yes

..I have hit strange issues pretty soon especially when user was
manipulating same mailbox from multiple devices at the same time.

Most issues was about corrupted indexes which was solved easily by just
putting them on local storage of each node:

 mail_location = maildir:/srv/mail/%d/%u:INDEX=/var/lib/dovecot/index/%d/%u

But I still hit issues like this one:

 dovecot: lmtp(6276, user at example.com): Error: Broken file /srv/mail/example.com/user at example.com/dovecot-uidlist line 8529: UIDs not ordered (8527 >= 8527)

Which I am not sure how serious it is or if it's possible to solve or
workaround?

Anyway because of the above and high possibility of GlusterFS
split-brains, I have decided to setup Dovecot Director according to the
docs [1] but I have a couple of questions:

- is custom monitoring still required? Poolmon [2] is 4 year old so I
  would suppose there's some progress since that?

- it's not possible to have same backends and directors in Dovecot
  <2.2.17. I can backport newer Dovecot for Ubuntu Trusty, so this is
  not an issue, but..

- documentation states that it still doesn't work for LMTP [3]?
  Which is probably important for my setup, because both Postfix servers
  are using dovecot-lmtp for mail delivery so there can be still some
  issues (but probably less frequent?) when both servers will deliver
  new mails for one user at once.
  So do I really have to split directors from backends?


Anyone has experience with clustered Dovecot setup?
Why is Dovecot behaving so bad when it pretends to be shared storage
friendly? Are these issues only specific for older Dovecot?
Or is there something wrong in my architecture design?

Thanks for any help,
Filip


---
[1] http://wiki2.dovecot.org/Director
[2] https://github.com/brandond/poolmon/
[3] "LMTP however doesn't currently support mixing recipients to both
     being proxied and store locally."

---
BTW if someone is interested in SaltStack, here are Salt formulas for
Dovecot + Postfix + GlusterFS + Roundcube + Mailman setup which we are
using:

https://github.com/tcpcloud/salt-formula-dovecot
https://github.com/tcpcloud/salt-formula-postfix
https://github.com/tcpcloud/salt-formula-roundcube
https://github.com/tcpcloud/salt-formula-glusterfs
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