EQUILOAD: a load balancing policy for clustered web servers

We present a new strategy for the allocation of requests in clustered web servers, based on the size distribution of the requested documents. This strategy, EquiLoad, manages to achieve a balanced load to each of the back-end servers, and its parameters are obtained from the analysis of a trace’s past data. To study its performance, we use phase-type distribution fittings and solve the resulting models using a new solution method for M/PH/1 queues that only requires solution of linear systems. The results show that EquiLoad greatly outperforms random allocation, performs comparably or better than the Shortest Remaining Processing Time and Join Shortest Queue policies and maximizes cache hits at the back-end servers, therefore behaving similarly to a “locality-aware” allocation policy, but at a very low implementation cost.