A Web Service for evaluation of load balancing strategies for distributed web server systems

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 becomes a bottleneck. So large web sites have multiple clusters, and it is best to have these clusters geographically distributed. This changes the problem to first select the nearest cluster and then do load balancing within the servers of that cluster. Of course, if all servers in a cluster are heavily loaded then another cluster should have been chosen. So the problem is more complex in such an environment.

Designing such a system involves making decisions about how the best server can be selected for a request such that the user gets a response in minimum time and how this request is directed to that server. In some strategies, a server is selected without taking into account any system state information, e.g. random, round robin e....