Research On QoS Control Of Web Server Cluster

HTTP is an important milestone in the rapid development process of Internet. Web QoS control becomes a very valuable research topic. Currently, IntServ and DiffServ are two important approaches for network QoS control and clustering becomes the future technology of constructing high performance Web server. However, the load-balancing Web clusters are not able to implement QoS-aware request dispatching. This thesis originates from QoS control of Web cluster. It's for the purpose of seeking end-to-end differentiate service solutions for Web applications.The thesis first analyzed the architectures and request dispatching strategies of the existing Web server cluster systems. Then we studied QoS control technologies on the Web cluster hosting single website. After analyzing the limitation of traditional M/M/1 and M/M/N queuing models, we enhanced Demand-driven Service Differentiation (DDSD) algorithm. The M/G/1 queuing model was used to replace the original M/M/1 model. We remodeled the cluster system and proposed an implementation scheme for parameter measurement, weight adjusting,admission control and request dispatching. Then we designed and implemented a Web cluster simulator based-on Network Simulator 2. We used that simulator to run a preliminary cluster simulation. The result shows that the Web cluster applied the algorithm can serve differentiate for different service classes on stretch factor metric. Finally, we combined IETF DiffServ model and QoS of Web cluster to deliver an end-to-end QoS solution.The innovative points of this thesis are: demonstrating enhanced algorithm of DDSD on Web cluster; proposing parameter estimation method for M/G/1-based Web server; using NS2 to create Web cluster simulation environment; combining network QoS and Web QoS into an end-to-end QoS solution.QoS control technology of Web server system is currently the frontier of network research. This thesis carries on a preliminary exploration to QoS control of Web cluster. Many topics need to be expanded for further research.