This Article 
 Bibliographic References 
 Add to: 
A Performance Study of Robust Load Sharing Strategies for Distributed Heterogeneous Web Server Systems
March/April 2002 (vol. 14 no. 2)
pp. 398-414

Replication of information across multiple servers is becoming a common approach to support popular Web sites. A distributed architecture with some mechanisms to assign client requests to Web servers is more scalable than any centralized or mirrored architecture. In this paper, we consider distributed systems in which the Authoritative Domain Name Server (ADNS) of the Web site takes the request dispatcher role by mapping the URL hostname into the IP address of a visible node, that is, a Web server or a Web cluster interface. This architecture can support local and geographical distribution of the Web servers. However, the ADNS controls only a very small fraction of the requests reaching the Web site because the address mapping is not requested for each client access. Indeed, to reduce Internet traffic, address resolution is cached at various name servers for a time-to-live (TTL) period. This opens an entirely new set of problems that traditional centralized schedulers of parallel/distributed systems do not have to face. The heterogeneity assumption on Web node capacity, which is much more likely in practice, increases the order of complexity of the request assignment problem and severely affects the applicability and performance of the existing load sharing algorithms. We propose new assignment strategies, namely adaptive TTL schemes, which tailor the TTL value for each address mapping instead of using a fixed value for all mapping requests. The adaptive TTL schemes are able to address both the nonuniformity of client requests and the heterogeneous capacity of Web server nodes. Extensive simulations show that the proposed algorithms are very effective in avoiding node overload, even for high levels of heterogeneity and limited ADNS control.

[1] P. Albitz and C. Liu, DNS and BIND. Cambridge, Mass.: O'Reilly and Associates, 1998.
[2] V.A. Álmeida, I.M.M. Vasconcelos, and J.N.C. Arabe, “The Effect of the Heterogeneity on the Performance of Multiprogrammed Parallel Systems,” Proc. Workshop Heterogeneous Processing, 1992.
[3] Alteon Web Systems,http:/, 2000.
[4] D. Andresen, T. Yang, and O.H. Ibarra, “Towards a Scalable Distributed WWW Server on Networked Workstations,” J. Parallel and Distributed Computing, vol. 42, pp. 91-100, 1997.
[5] M. . Arlitt and L. Williamson Carey, “Internet Web Servers: Workload Characterization and Performance Implications,” IEEE/ACM Trans. Networking, vol. 5, no. 5, pp. 631-645, Oct. 1997.
[6] M. Baentsch, L. Baum, G. Molter, S. Rothkugel, and P. Sturm, “Enhancing the Web's Infrastructure: From Caching to Replication,” IEEE Internet Computing, vol. 1, no. 2, pp. 18-27, Mar.-Apr. 1997.
[7] A. Bestavros, “WWW Traffic Reduction and Load Balancing through Server-Based Caching,” IEEE Concurrency, vol. 5, no. 1, pp. 56-67, Jan.-Mar. 1997.
[8] V. Cardellini, M. Colajanni, and P. Yu, "Dynamic Load Balancing on Web-Server Systems," IEEE Internet Computing, Vol. 3, No. 3, May/June 1999, pp. 28-39.
[9] V. Cardellini, M. Colajanni, and P. Yu, "DNS Dispatching Algorithms with State Estimators for Scalable Web-Server Clusters," World Wide Web J., vol. 2, no. 2, July 1999, pp. 101-113.
[10] T.L. Casavant and J.G. Kuhl,“A taxonomy of scheduling in general-purpose distributed computing systems,” IEEE Trans. on Software Engineering, vol. 14, no. 2. Feb. 1988.
[11] Cisco's DistributedDirector,http:/, 2001.
[12] Cisco's LocalDirector,http:/, 2001.
[13] M. Colajanni, P.S. Yu, and D.M. Dias, "Analysis of Task Assignment Policies in Scalable Distributed Web-Server Systems," IEEE Trans. Parallel and Distributed Systems, Vol. 9, No. 6, June 1998, pp. 585-600.
[14] Common Logfile Format, , July 1995.
[15] M.E. Crovella and A. Bestavros, “Self-Similarity in World Wide Web Traffic: Evidence and Possible Causes,” IEEE/ACM Trans. Networking, vol. 5, no. 6, pp. 835-846, Dec. 1997.
[16] P. Barford, A. Bestavros, A. Bradley, and M.E. Crovella, “Changes in Web Client Access Patterns: Characteristics and Caching Implications,” World Wide Web J. vol. 2, no. 1, pp. 15-28, Jan. 1999.
[17] D.M. Dias, W. Kish, R. Mukherjee, and R. Tewari, “A Scalable and Highly Available Server,” Proc. IEEE Computer Conf. (COMPCON), Mar. 1996.
[18] D.L. Eager, E.D. Lazowska, and J. Zahorjan, "Adaptive Load Sharing in Homogeneous Distributed Systems," IEEE Trans. Software Eng., vol. 12, no. 5, pp. 662-675, May 1986.
[19] F5 Networks,http:/, 2001.
[20] R. Fielding, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and T. Berners-Lee, “Hypertext Transfer Protocol - HTTP/1.1,” RFC 2616, June 1999.
[21] Foundry Networks,http:/, 2001.
[22] G. Hunt et al., "Network Dispatcher: A Connection Router for Scalable Internet Services," Proc. 7th Int'l World Wide Web Conf., 1998; available online at.
[23] P. Krueger and N.G. Shivaratri, "Adaptive Location Policies for Global Scheduling," IEEE Trans. Software Eng., Vol. 20, No. 6, June 1994, pp. 432-444.
[24] T.T. Kwan, R.E. McGrath, and D.A. Reed, "NCSA's World Wide Web Server: Design and Performance," Computer, Vol. 28, No.11, Nov. 1995, pp. 68-74.
[25] A. Iyengar et al., "High-Performance Web Site Design Techniques," IEEE Internet Computing, vol. 4, no. 2, Mar./Apr. 2000.
[26] D.A. Menascé, D. Saha, S.C. da Silva Porto, V.A.F. Álmeida, and S.K. Tripathi, “Static and Dynamic Processor Scheduling Disciplines in Heterogeneous Parallel Architecture,” J. Parallel and Distributed Computing, vol. 28, pp. 1-18, 1995.
[27] D. Mosedale, W. Foss, and R. McCool, "Lessons Learned Administering Netscape's Internet Site," IEEE Internet Computing, Vol. 1, No. 2, Mar.-Apr. 1997, pp. 28-35.
[28] R. Mukherjee, “A Scalable and Highly Available Clustered Web Server,” High Performance Cluster Computing: Architectures and Systems, vol. 1., R. Buyya, ed., Prentice Hall, 1999.
[29] J.E. Pitkow, “In Search of Reliable Usage Data on the WWW,” Proc. Sixth Int'l WWW Conf., Apr. 1997.
[30] Radware Networks, 1899/com1899.htmhttp:/ /, 2001.
[31] K. Ramamritham, J.A. Stankovic, and W. Zhao, “Distributed Scheduling of Tasks with Deadlines and Resource Requirements,” Trans. Computers, vol. 38, no. 8, Aug. 1989.
[32] Resonate Global Dispatcher,http:/, 2001.
[33] R.J. Schemers, "lbmnamed: A Load Balancing Name Server in Perl," Proc. 9th Systems Administration Conf., Usenix Assoc., Berkeley, Calif., Sept. 1995.
[34] T. Schroeder, S. Goddard, and B. Ramamurthy, “Scalable Web Server Clustering Technologies,” IEEE Network, pp. 38-45, May-June 2000.
[35] A. Singhai, S.-B. Lim, and S.R. Radia, “The SunSCALR Framework for Internet Servers,” Proc. IEEE 28th Int'l Symp. Fault-Tolerant Computing, 1998.
[36] H. Schwetman, CSIM18: The Simulation Engine. Mesquite Software Inc. 1999.
[37] G.K. Zipf, Human Behavior and the Principles of Least Effort. Reading, Mass.: Addison-Wesley, 1949.

Index Terms:
load balancing, performance analysis, domain name system, distributed systems, global scheduling algorithms, World Wide Web
M. Colajanni, P.S. Yu, "A Performance Study of Robust Load Sharing Strategies for Distributed Heterogeneous Web Server Systems," IEEE Transactions on Knowledge and Data Engineering, vol. 14, no. 2, pp. 398-414, March-April 2002, doi:10.1109/69.991724
Usage of this product signifies your acceptance of the Terms of Use.