A client-aware dispatching algorithm for web clusters providing multiple services
Emiliano Casalicchio, Michele Colajanni · 2001
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-awarepolicy (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 classies the clientrequestson 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 eective 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, veryhardtoachieveina highly dynamic system suchasaWeb site. Categories and Subject Descriptors C.2.4 [######## ############# ########]: Distributed Systems; C.4 [########### ## #######]: Design studies; H.3.5 [########### ####### ### #########]: Online Information Services|Web-based services General Terms Algorithms, Design, Performance Keywords Load balancing, Dispatching algorithms, Clusters Copyright is held by the author/owner. WWW10, May 1-5, 2001, Hong Kong. Copyright 2001 ACM 1-58113-348-0/01/0005 ...$5.00. 1.