[afnog] Clustering Exim

SM sm at resistor.net
Thu Feb 25 19:23:33 UTC 2010

Hi Phil,
At 09:11 25-02-10, Phil Regnauld wrote:
>         Not quite, CARP is used for failover scenarios, but can also be
>         used for load balancing.


>         It depends whether you want to enforce the delivery by controlling
>         the active IP, or you want to leave that up to the remote sender
>         Which is why MX based load balancing doesn't work that well since
>         many badly written MTAs and spammers order the results returned
>         by the DNS and send email to the first IP in numerical order or
>         similar.

There's not much we can do about that.  We could use DNS tricks to 
return different IP addresses or low TTLs.

>         You can't unless you share the filesystem at block level (DRBD)
>         or VFS level (NFS on a shared backend) or using GFS or similar.
>         ZFS snapshots face the same problem as scheduled rsync replications.

I won't suggest NFS.  I would go for a dedicated storage system (SAN) 
if cost is not an issue.  It is worth considering whether you need 
100% availability for each spool.

>         How do you do that without either a) shared storage or b) synchronous
>         block replication ?

Unless the failure rate is significant, it is cheaper to move disks 
as this is SMTP.

Queue management is also important as bounce management and maybe per 
domain queues may be needed once the messages are accepted.


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