Adaptive Control of Apache Web Server

Traffic to a Web site can vary dramatically. At the same time it is highly desirable that a Web site is reactive. To provide crisp interaction on thin clients, 150 milliseconds has been suggested as an upper bound on response time. Unfortunately, the popular Apache Web server is limited in its capabilities to be reactive under varying traffic. To address this problem, we design in this paper an adaptive controller for the Apache Web server. A modified recursive least squares algorithm is used to identify system dynamics and a minimum degree pole placement controller is implemented to adjust the maximum number of concurrent connections. Experimentally, we show that the controller effectively regulates the reply time of HTTP connection requests, and hence provides reactive response, by limiting the maximum number of connections accepted by an Apache Web server.