Scalability Through Load Balancing

Scalability is the ability of a system to meet the performance demands of an increasingly larger user community. A single processor, no matter how fast, can only service a finite number of user requests with some degree of performance. Adding multiple processors to a box can buy some additional performance but not really increase the overall scalability of the overall system. To increase the scalability of the system in a meaningful way requires the introduction of additional processing units (boxes), one of which is to be used as an HTTP dispatcher. All requests will come in to the dispatcher, and the dispatcher will direct the request to the least busy box in the cluster of processing units. Many Web sites today handle more than a million requests a day using old hardware (66-MHz 486s and 100-MHz Pentiums) and by running large clusters of them (20–25).