Design of a Fuzzy PI Controller to Guarantee Proportional Delay Differentiation on Web Servers

PI controller has attracted researchers in industrial control processes because of its simplicity and robust performance in a wide range of operating conditions. It has been used to provide proportional delay differentiation on web servers in pervious work. However, PI controller can not achieve satisfactory results due to (1) the web server’s non-linearity properties (2) the difficulty of building an accurate model for the web server. To address these issues, a nonlinear fuzzy PI controller is proposed in this paper, which has the advantage of fuzzy controller while maintaining the simplicity and robustness of classical PI controller. The control gains of the proposed controller can be self-tuned according to the delay ratio error and the error varying rate which are measured online periodically. The proposed fuzzy PI controller can reduce the settling time and is more robust against strong uncertainties. We implement the fuzzy PI controller by modifying the source code of Apache web server. The experimental results demonstrate that our fuzzy PI controller outperforms the classical PI controller in several aspects. KeywordsQoS, Fuzzy PI controller, Web servers