Saturday, 28 June 2008

Load Balancers

There are two ways to have the distribute the load on your network using hardware or software load balancers.

The hardware load balancer some advantages over software load balancers the first is that its independent of the operating system and there for as better throughput than a software one loaded one the second is that can do some checks against the returned code as an example if it sees 404 error page you can configure it to remove that server from the webfarm.

The best hardware load balancer is Cisco Application Control Engine (ACE) module or a Cisco 7600 series router.

Software based load balancers are cheaper to use as they require no Cisco training to use or special hardware, however since they do not have active probes if a web-server or other balanced service starts to return an error message you are unaware of and my issue this error to customers for awhile before you find out.

So from a design point of view to have the highest level of uptime you need two hardware load balancers these can be in active/standby or active/active mode and both to have probes configure to remove unresponsive or error generating servers from the balanced farm.

One last thing to add is if you are using a round robin DNS where you have geographical server farms so that content is provided from near is physical server farm.

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