Dynamic Load Balancing in Geographically Distributed Heterogeneous Web Servers

With ever increasing web traffic, a distributed Web system can provide scalability and flexibility to cope with growing client demands. Load balancing algorithms to spread the load across multiple Web servers are crucial to achieve the scalability. Various domain name server (DNS) based schedulers have been proposed in the literature, mainly for multiple homogeneous servers. The presence of heterogeneous Web servers not only increases the complexity of the DNS scheduling problem, but also makes previously proposed algorithms for homogeneous distributed systems such as round robin no directly applicable. These leads us to propose new policies, called adaptive TTL algorithms, that take into account of both the uneven distribution of client request rates and heterogeneity of Web servers to adaptively set the TTL value for each address mapping request. Extensive simulation results show that these strategies are robust and effective in balancing load among geographically distributed heterogeneous Web servers.