Dovecot cluster using GlusterFS

[Filip Pytloun]

Hello Alessio and Gordon, thank you for answers.

Dsync-based architecture looks promising, but I would preffer to stay
with GlusterFS for now as I also use it as a storage for other
components.

So director is the way to go, I don't want to setup more than two nodes
to keep this setup as simple as possible - so I will probably update to
2.2.19 and have director and backend on the same servers (and Dovecot
instance).

I asked about poolmon, because I think that Dovecot should have some
internal mechanism on how to recognize broken backend by default.
But if it works nicely, I am going to use it as well :-)

> At the moment, I cannot recognize the requirement for using lmtp over
> the directors. When using postfix for delivering e-mails to the
> backend, do this directly with an corresponding MX record.

I have two MX records of the same weight with postfix using dovecot-lmtp
for delivery. So that's why I wanted to use LMTP over directors.
Using lower weight for second MX is an option, but not truly
master-master setup :-)

Filip

On 2015/12/06 02:31, Alessio Cecchi wrote:
> Il 05.12.2015 10:42 Filip Pytloun ha scritto:
> >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
> 
> With only these setting you don't solve the problem of shared storage.
> 
> >..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?
> 
> You need Director for POP/IMAP and also LMTP so you can solve all "Broken
> file" and "corrupted indexes" problems.
> 
> >
> >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?
> 
> For me poolmon works fine.
> 
> >- 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..
> 
> Yes is possibile (also with < 2.2.17), create two instances, like dovecot
> and director, two config directory /etc/dovecot/ and /etc/director/ and bind
> on differents IPs.
> 
> >- 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?
> 
> I'm running Director and backend on the same server for POP/IMAP, and in
> another configuration and Director for LMTP is on the same server (but with
> 2.2.19).
> 
> >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?
> 
> You need Director, Dovecot has not problems with shared storage, big
> installation are always using shared storage (like NFS).
> -- 
> Alessio Cecchi
> Postmaster AT http://www.qboxmail.it
> http://www.linkedin.com/in/alessice
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