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The overall increase in traffic on the World Wide Web causes a lengthening of client requests to popular Web sites, especially in conjunction with special events. Single node platforms that do not replicate information content cannot provide the needed scalability to handle large traffic volumes and to match rapid and dramatic changes in the number of clients. The need to improve the performance of Web-based services has produced a variety ofnovel content delivery architectures. This paper will focus on locally distributed Web systems, where the server nodes reside at a single location. After years of proposals of new routing mechanisms, policies and system solutions (the first dated back to1994 when the NCSA Web site had to face the first million of requests per day) many problems concerning multiple server architectures for Web sites have been solved. Other issues remain to be addressed especially at the network application level, but the principle techniques and methodologies for building scalable Web content delivery architectures placed in a single location are settled now. This paper classifes and describes main mechanisms to split the traffic load among the server nodes, discussing both the alternative architectures and the load sharing policies. To this purpose, it focuses on architectures, internal routing mechanisms, and dispatching request algorithms for designing and developing scalable Web-server systems and identifies some of the open research issues associated with the use of distributed systems for highly accessed Web sites.
By: Valeria Cardellini, Emiliano Casalicchio (University of Roma Tor Vergata) Michele Colajanni (University of Modena), Philip S. Yu
Published in: Computing Surveys , volume 34, (no 2), pages 263-311 in 2002
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