Abstract
Many large web sites get millions of hits everyday. They need a scalable web server
system that can provide better performance to all the clients that may be in different
geographical regions. Common approach to improve performance is to have fully
replicated web server clusters in different geographical regions with replicated
servers. In such an environment, one of the most important issues is selecting a server
for servicing a request. Client requests should be directed to a server such that the
time taken for servicing the request can be minimised. Different policies are possible
for server selection and it is difficult to determine the impact of different policies.
In this paper, we describe a web service that can be used to evaluate the performance
of different schemes. We provide a web based testbed to perform this task. This
service utilizes a dedicated testbed that emulates the World Wide Web and on which
the performance of various strategies can be studied. A user gives the values of
different network and load parameters and the specifics of the policy. The testbed is
configured to emulate a web server system using the specified policy and performance
testing is done. Data from the tests is collected, analyzed and graphically displayed to
the user. The service also allows new approaches to be tested.
Introduction
Number of users accessing the Internet is increasing quite rapidly and it is common to
have more than 100 million hits a day for popular web sites. For example,
netscape.com website receives more than 120 million hits a day. The number of users
is expected to continue increasing at a fast rate and hence any website that is popular,
faces the challenge of serving very large number of clients with good performance.
Full mirroring of web servers or replication of web sites is one way to deal with
increasing number of requests. Many techniques exist for the selection of the nearest
web server from the client’s point of view. Ideally, selection of best server should be
done transparently without the intervention of the user.
Many of the existing schemes do only load-balancing. These schemes assume that the
replicated site has all the web servers in one cluster. This is alright for medium sized
sites, but beyond a certain amount of traffic, the connectivity to this one cluster



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