Cyrus IMAP and MySQL mailboxes (Building load-balancing cluster)

[Chris St. Pierre]

On Mon, 20 Nov 2006, Marcelo Maraboli wrote:

> Andrew
>
> thanks for the "scalable" Cyrus solutions, but I´m wondering
> what can be done for Availability solutions ??
>
> What if an IMAP server dies (we had this happen) ??
>
> We have a Solaris Server with a RAID5 disk array storing the
> MBOX, but the server died....so downtime was a bit huge..
>
> I wan to build a 100% available IMAP solution...is there any?

Andrew's options 1 and 3 both ensure very high availability (with a
failover mupdate server in the murder).  We use a SAN for mail
storage, and then have two IMAP servers that do failover, so if one
dies the other picks up.  This is probably the simplest high
availability solution.  Add a second failover SAN (or use a clustering
SAN solution with multiple, failsafe nodes) and you'll have extremely
high uptime.  Clients that use persistent IMAP connections will have
problems, but those are few and far between.

Even with all that, 100% availability might be setting your sights a
little high. :)

Chris St. Pierre
Unix Systems Administrator
Nebraska Wesleyan University


> Andrew Morgan wrote:
>> On Fri, 17 Nov 2006, Igor Zhbanov wrote:
>> 
>> > 2006/11/17, Adam Tauno Williams <adam at morrison-ind.com>:
>> > > > Yes, I know how failover cluster works. But what if one server
>> > > > (active) can't process such a load? Suppose, we plan to have 100 000
>> > > > users working actively with mail. I understand that it is possible to
>> > > > use one monstrous server to take all of the load, but I am interested
>> > > > in load-balancing solution on relatively inexpensive servers.
>> > >
>> > > (a) SANs are not that expensive.
>> > > (b) SANs are *WAY* *WAY* more reliable than *ANY* storage solution you
>> > > can build yourself for the same amount of money.  If you really don't
>> > > believe that you need to lay of smoking the good stuff.  And (b.1) - if
>> > > you have that many users but can't afford a SAN...
>> > > (c) Then there is Cyrus replication and there is GFS.  There was long
>> > > thread on Cyrus IMAP, HA, & GFS just back in October.
>> > >
>> > >
>> > > > And what
>> > > > about slow anti-viruses for 100 000 users' mail? Or to use
>> > > > load-balanced front-ends connected to single SAN and connected to
>> > > > anti-virus load-balanced cluster? :-)
>> > >
>> > > It doesn't require a cluster to load balance SMTP,  traditional and well
>> > > established technologies will do that for you.  Setup multiple SMTP
>> > > servers and publish multiple MX records.
>> >
>> > Yes, I can use DNS-based load-balancing to spread load to several
>> > frontends. But what about backends? :-) How to balance load for them?
>> 
>> There are basically 3 known solutions to building a scalable Cyrus system:
>> 
>> 1. Cyrus murder + Cyrus replication.  Cyrus murder distributes mailboxes
>> across multiple backend servers.  The murder backend servers could use local
>> storage, or be connected to a SAN, non-shared file system.  The murder
>> frontends (you can run as many frontends as you want) accept incoming IMAP
>> and LMTP connections and route them to the correct murder backend server.
>> You could use DNS round-robin to load balance connections between the murder
>> frontends, or you could use something more sophisticated like LVS or a
>> hardware-based network load balancer.  Use Cyrus replication to keep a backup
>> copy of each murder backend.
>> 
>> 2. Cyrus replication + perdition/nginx.  Manually distribute your mailboxes
>> between multiple Cyrus servers (in a non-murder configuration). Use Perdition
>> or nginx to route incoming IMAP connections to the correct server.  Use Cyrus
>> replication to keep a backup copy of each murder backend.
>> 
>> 3. Cyrus + SAN + clustering.  Use multiple servers in a cluster, connected to
>> a SAN.  Several different people have attempted this according to recent
>> mailing list postings here.  The only successful cluster I'm aware of was a
>> Tru64 cluster.
>> 
>>     Andy
>> ----
>> Cyrus Home Page: http://cyrusimap.web.cmu.edu/
>> Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
>> List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
>> 
>
> -- 
> Marcelo Maraboli Rosselott
> Jefe Area de Redes y Comunicaciones (Network & UNIX Systems Engineer)
> Ingeniero Civil Electronico, CISSP       (Electronic Engineer, CISSP)
>
> Direccion Central de Servicios Computacionales (DCSC)
> Universidad Tecnica Federico Santa Maria        phone: +56 32 2654071
> Chile.                 http://www.usm.cl   http://elqui.dcsc.utfsm.cl
> ----
> Cyrus Home Page: http://cyrusimap.web.cmu.edu/
> Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
> List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
>