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

[Marcelo Maraboli]

Dear Sarah

thank you for your thorough answer !

maybe we can wait and see if Cyrus 2.3.7 and mupdate
can do the job along with FreeBSD+PEN+VRRPD...i´ll test it.

best regards,

Sarah Walters wrote:
> Marcelo et al, 
> 
>> -----Original Message-----
>> From: info-cyrus-bounces at lists.andrew.cmu.edu 
>> [mailto:info-cyrus-bounces at lists.andrew.cmu.edu] On Behalf Of 
>> Marcelo Maraboli
>>
>> thanks for the input, I know wishing 100% is only available
>> with a gooooogle size amount of money ;), but I am looking
>> for a CYRUS IMAP server solution similar to a load balancing
>> web server farm...i.e:
>>
>> - a Load balancing server (PEN in Freebsd if you like) that
>> will direct an IMAP session to ANY of a group of IMAP servers,
>> all of which have access to a central storage of user MBOXs.
>>
>> So if any of the IMAP (backend) server dies, the load balancer with
>> automatically not forward any new requests to that server
>> and users won´t notice any downtime..
>>
>> this is diferent from Andrew´s solution number 1, since ANY of
>> the backend IMAP server should accept connections for ANY user.
>>
>> examples:
>> http://siag.nu/pen/vrrpd-linux.shtml
>> http://redundancy.org/fbsd_lb.html
>>
>> can IMAP be set up this way ??
>>
>> regards,
>>
> 
> This need is why I suggested beefy servers rather than the Murder, which I don't consider sufficiently highly available due to actually being a number of discrete servers at the back end. Great for load balancing, useless for instant failover in case of server loss.
> 
> In short, as I understand it Cyrus cannot be set up this way. Only a single machine can have write privileges to the mailboxes database at a time. The only way I can see to do this is to use NFSv4 which is supposed to get the locking correct. Then, assuming the database is closed between changes (can a developer please confirm whether it is kept open by master or not?) you should be able to run multiple IMAP servers over the same filesystem stored on a NAS (network-attached storage, as opposed to SAN). That is the only way I can think of to do what you are after. You would need two NAS boxes, ideally in separate buildings, with live mirroring (10 Gb fibre or copper connection between) and a bunch of cheap servers in each building all load-balanced. You should be able to lose a complete data centre and just keep running at 50% capacity as long as your network is properly routed (with redundancy in case of an idiot with a spade cutting through your fibre of course).
> 
> It's expensive, but it should work if the database is not held open. If it is, then you need to look at a different email product. Cyrus is a great server, but if you need five 9s reliability then you have to pay for it. You could always look at an appliance - dedicated hardware is often more reliable and at least if it goes down you can scream at the vendor and cover your butt that way.
> 
> Regards,
> Sarah Walters
> ----
> Cyrus Home Page: http://cyrusimap.web.cmu.edu/
> Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
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> 

-- 
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