Using a Cluster for Efficient Scalability Evaluation of Multithreaded and Event-Driven Web Servers

Scalability of a Web server is pertinently influenced by the architecture of Web server software system and/or Web server cluster. In this paper, a Web server cluster system is used to evaluate the vertical (scale-up) and horizontal (scale-out) scalability properties of multithreaded Apache and event-driven μserver Web server. Servers are scaled up by adding more processor cores to the server node and scaled out by adding more server nodes to the cluster. A number of experiments are thus performed on nine different cluster configurations. The relative capacity is measured against the number of active processor cores. The analysis of calculated relative capacity shows that scalability makes a transition from ‘near-linear’ to sub-linear for both Web servers as more processor cores and/or server nodes are added. While comparing the throughput, it was found that μserver exhibits slightly better performance than Apache on all nine server cluster configurations; although the increments in scalability achieved by means of vertical (scale-up) and horizontal (scale-out) scalability are almost equivalent.