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Controlling the Response Time of Web Servers

Internet server provisioning is a very challenging problem for content providers and large server farms. In this paper we investigate the control theoretic approaches of managing servers in order to satisfy a required Quality of Service (QoS). We compare between two widely used models in the literature and our proposed simple technique. First model is a queueing based M/G/1 model with a PI controller. The second technique represents the server as a second order system and estimates the system parameters on line every sampling period. The estimated parameters are used in the design of a first order filter/controller in order to track the required QoS. Finally we present a simple technique based on the Additive Increase Multiplicative Decreases used in TCP congestion avoidance. We use simulation to compare these three techniques. Surprisingly, the AIMD performs the best among these three and it requires the least computation overhead among the three.