DNS load balancing

Michael Menge michael.menge at zdv.uni-tuebingen.de
Tue May 11 09:03:40 EDT 2010

Quoting Andre Nathan <andre at digirati.com.br>:

> Hello
> I'm setting up a two-machine cyrus cluster using OCFS2 over DRBD. The
> setup is working fine, and I'm now considering the load balancing
> options I have.

For Clustering Cyrus have a look at

I have no experiance with OCFS2 but an active-active cyrus cluster
on a shared filesystem is tricky at best.

> I believe the simplest option would be to simply rely on DNS load
> balancing. However, for this to work, I need to consider what happens
> when one of the cluster nodes fails, regarding the clients which access
> the cluster:

Depending on the OS and Networksetting this can take some time,
because the OS and relaying DNS-server may cache the result.

>  - Will IMAP and POP3 clients automatically try the second DNS entry if
>    connecting to the first one fails?
>  - Will the LMTP client also do this? I'm using the postfix LMTP client
>    for delivery.

The will try to reconnect but might use the old DNS answer.

> Does any one have experience with this kind of setup?

We use this kind of loadbalancing for web-proxys and smtp-server
but if one node fails there are some clients that try to connect
the failed node

You should take a look at ClusterIP, Cyrus Murder and Cyrus Replication

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M.Menge                                Tel.: (49) 7071/29-70316
Universität Tübingen                   Fax.: (49) 7071/29-5912
Zentrum für Datenverarbeitung          mail:  
michael.menge at zdv.uni-tuebingen.de
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72074 Tübingen
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