MDDR: a solution for improving the scalability of dispatcher-based Web server cluster

The dispatcher-based Web server cluster has been widely used to increase a Web server´s performance. When the count of real servers adds up to a certain number, the dispatcher becomes the bottleneck of the whole system, which stops the system´s performance from increasing and sets a limit to the system´s scalability. In order to tackle this problem, the paper produces a method called MDDR (multiple dispatchers with direct routing) and implements a prototype MDDR. In MDDR, each of the multiple dispatchers can have an independent real server group. Through assigning requests from clients to every dispatcher, the burden of each dispatcher in MDDR is decreased, which improves the scalability of the cluster system. Measurements show that when the dispatchers become the bottleneck of the cluster system, adding more dispatchers eliminates the bottleneck and makes the system scalable again.