If a server goes down, traffic can be automatically directed to another server " that's high availability. If you want to take a server down or apply a patch, in the real world if you don't have a load balancer you have to tell users the server's going down or do the administration at night. And a load balancer can be a security gateway, to stop the bad guys that a firewall doesn't. These are not trivial benefits to the people running server farms.
Networking Pipeline: How does a load balancer catch what a firewall doesn't?
Kopparapu: Most enterprises keep their Web servers inside the firewall, and end up having to punch a hole " typically through Port 80 " to let traffic in. Ultimately, that can become a gateway for the bad guys. A firewall cannot distinguish different types of traffic, while a load balancer can look deeper into the packet and even into transactions, to determine what is a good or bad connection.
Networking Pipeline: Isn't there a performance hit from using load balancers?
Kopparapu: Sure, there's always a performance hit " anyone who tells you they have a "wire speed" load balancer is selling you marketing hype. But while you can't offer wire speed on every port, you can offer high performance levels. We offer 4 to 8 Gbps throughput, and that's plenty. You have to ask if that satisfies your requirements, especially weighed against the costs of downtime or taking a hit when a server goes down.