round-robin and multi MX practicalities

[peter at icke-reklam.manet.dot..nu]

David Zade <dzade at rcn.com> wrote:
> Beware, I do not believe roundrobin will work for failing over to a backup
> server.  It just hands out the addresses in rotating order.  It will still
> handout the address of the dead server.
Correct. Any decent application however will detect that this is a dead
server and try the next address given in the reply.
(remember that all addresses is returned in the dns reply, only the order that 
changes with round-robin)


> Second, mail clients, use\d on the user desktop, don't typically use SMTP to
> receive messages, they use POP3, IMAP, or a custom protocol,  They may use
> SMTP to send, but I think that address is resolved to a specific server 'A'
> record.  The MX record is used by SMTP server to forward mail to other SMTP
> servers.
Also correct. However even here you can create a 'A' record that consist
of several addresses. Again, any decent application will detect dead
servers and go on with the next.

But i do not see the problem, why not use smtp hosts that will stay alive ?


Regards
Peter h

> You want a load balancing services, either one that redirects packets, or
> provides s DNS service.  Either way the load balancer would have to monitor
> server (and service) availablility, and alter forwarding decisions based on
> the monitor info.

> DAvid zADE
> dzade at rcn.com
> Alex Miller <bind at lists.cybergood.net> wrote in message
> news:003001bf7d84$9d2d25c0$867c06d1 at aranea.cybergood.net...
>> I had a server go down recently. It's the
>> second failure I've had in 6 months both
>> times were my error. What a different and
>> refreshing world Linux is (as compared to
>> Windows not other Unixes), when I can no
>> longer blame the OS for down time!!
>>
>> Anyway, I want to set up a SECOND server
>> for the next time I screw up.
>>
>> Round-robining should work fine for a web
>> server, if one is down, the other is available,
>> that I understand, but multiple MX records
>> are a different story.
>>
>> If a user has not picked up mail on server A
>> and then server A goes down, and mail gets
>> handeled by server B, mail might get lost
>> when server A goes back online. All the
>> mail that collected on server B during server
>> A's absence, will not be collected once server
>> A is handling collections.
>>
>> Therefore I must, I presume, synchronize the
>> user mail on server A and server B. This could
>> be rather scary I would think, and I imagine
>> all sorts of nasty file locking problems, etc.
>>
>> What solutions are being used to use two servers
>> for web redundancy and email redundancy?
>>
>> Alex Miller
>>
>> -----------------------------------------
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>>
>>






-- 
--
Peter Håkanson         
Manet Networking      (At the Riverside of Gothenburg, home of Volvo)
Sorry about my e-mail address, but i'm trying to keep spam out.
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