Load Balancers

Use load balancers to distribute overall load on your Web or application servers, or to distribute demand according to the kind of task to be performed. If, for example, you have a variety of dedicated applications and hence different application servers, you might use load balancers according to the kind of application the user requests.

If you have multiple data centers, you should consider geographic load balancing. Geographic load balancing distributes load according to demand, site capacity, and closest location to the user. If one center should go down, the geographic load balancer provides failover ability.

For load balancers on Web farms, place the hardware load balancers in front of the servers and behind routers because they direct routed traffic to appropriate servers. Software load balancing solutions reside on the Web servers themselves. With software solutions, one of the servers typically acts a traffic scheduler.

A load balancing solution is able to read headers and contents of incoming packets. This enables you to balance load by the kind of information within the packet, including the user and the type of request. A load balancing solution that reads packet headers enables you to identify privileged users and to direct requests to servers handling specific tasks.

You need to investigate how dynamically the load balancer communicates with all the servers it caters to. Does the scheduler ping each server or create “live” agents that reside on the servers to ascertain load data? You should also examine how the load balancer parses TCP packets. Pay attention to how quickly the load balancer can process a packet. Some load balancers will be more efficient than others. Load balancer efficiency is typically measured in throughput.