A client-aware dispatching algorithm for web clusters providing multiple services

Abstract

The typical Web cluster architecture consists of replicated back-end and Web servers, and a network Web switch that routes client requests among the nodes. In this paper, we propose a new scheduling policy, namely client-aware policy (CAP), for Web switches operating at layer-7 of the OSI protocol stack. Its goal is to improve load sharing in Web clusters that provide multiple services such as static, dynamic and secure information. CAP classi es the client requests on the basis of their expected impact on main server resources, that is, network interface, CPU, disk. At run-time, CAP schedules client requests reaching the Web cluster with the goal of sharing all classes of services among the server nodes. We demonstrate through a large set of simulations and some prototype experiments that dispatching policies aiming to improve locality in server caches give best results for Web publishing sites providing static information and some simple database searches. When we consider Web sites providing also dynamic and secure services, CAP is more e ective than state-of-the-art layer-7 Web switch policies. The proposed client-aware algorithm is also more robust than server-aware policies whose performance depends on optimal tuning of system parameters, very hard to achieve in a highly dynamic system such as a Web site.