Re: Mail attachments in a cluster environment

[Daniel Watts <d@xxxxxxxxxxxxx>]

Alexandros Vellis wrote:

Thank you for this - we've just found out that haproxy can set a cookie
on the client side that tells the load balancer which server to connect
to. HAproxy is clever enough to know that if it tries to connect to the
same server and fails, it ignore the cookie and connect to another server.
    

A hah. Sounds nice.

"pound" has a similar feature, and it can actually maintain the session
mapping itself without any additional cookie on the client.
  

Yep, so does HAproxy but what happens if the client connects to the OTHER load balancer during the same session? Either the client needs to have some state information (a cookie) or the two servers need to share some state information. haproxy doesn't have the ability to send such information between instances so we had to go for client side state tracking. Does Pound have this facility?

The only thing we cannot yet distribute is the
actual imap storage - however with drdb (http://www.drbd.org/) this
might soon be possible....may be.
    

I don't know anything at all about drbd, but you might also want to look
at options such as Cyrus Murder replication (application-level) or using a
clustering filesystem such as GFS or ZFS (filesystem-level). The
info-cyrus mailing list has a lot of posts about people with such
experiences.
  

Do you know of GFS/ZFS being  used in a large production environment with success?

I've heard of Murder (is is only for the cyrus IMAP server?). The other solution was to go for a big NetApp type thing - ie a single point of failure that is built not to fail. Still seems a bit of a 'keep fingers crossed' setup but some people swear by them.

Some interesting stuff here, Thanks =)

Daniel

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