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RE: Server Redundancy
From: "John Ferriby" <john () ferriby com>
Date: Thu, 7 Aug 2003 10:40:53 -0400


Rob Pickering said:

I've used both the route hack based and commercial NAT load 
balancers, and they both have their place.

Yes, one size does not fit all.
 
Commercial NAT based load balancers are able to do things like 
distribute requests according to actual measured server response 
characteristics. This is great if you have clusters of servers with 
different specs but want to extract the best performance under peak 
load from the whole cluster. It also helps if you are running complex 
services where individual servers can develop a pathological slow but 
not failing response for some reason.

They are also able to do the kind of service polling as above and 
react quicker to a down server than one which relies on routing 
protocols.

Quite true.   A product not mentioned in previous posts would be the
Radware WSD, which has been great for my applications.  See it at
www.radware.com   These come in distrubted flavors too.

Also not mentioned previously would be the Netscaler, www.netscaler.com 

If you are running complex web services (think expensive per server 
sw licences etc) then the investment in a pair of redundant load 
balancers for the front end to give more consistent performance under 
load as well as resilience can look very sane indeed.

Oh, yes.   They make a lot of sense in large streaming environments.

-John


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