which load balancer

[kwijibo at zianet.com]

Omar Armas wrote:
> Hi, I want to set up a farm of mail servers with load balancing.
> Which method is the best under the following conditions:
> 
> -Services load balanced: SMTP, POP and IMAP.
> -3 nodes initially and growth to 5 or 6 nodes in a few weeks. may more 
> come later.
> -Linux (Qmail-LDAP as MTA)
> 
> 
> Which method for load balancing would be best for this? DR, NAT, TUN?
> I have a LVS/DR for HTTP, and remember to have read that LVS/NAT doesn´t 
> scale very well with large installations. Is that true? Is it solved?
> What about tunneling?
DR will scale the best.  In a NAT configuration all the return traffic
from the nodes has to pass back through the LVS.  In a DR configuration the
nodes themselves respond to the client.  There is nothing to solve in
the NAT configuration because nothing is broken.  NAT by it's very nature
just doesn't scale well.
> 
> Is LVS/DR the only in which nodes have to be Linux? For what I´ve read, 
> in NAT and TUN I can use other OS(FreeBSD), is that right?
> 
No. You can have whatever OS that has the capability to ignore ARPS.
FreeBSD nodes in DR configuration work fine you just need to use the
-arp flag with ifconfig.  I believe you can even use Windows as a node
if you so desire.  Never tried it but I don't see a reason why it would
not work.

Steve