Scaling the Web

D evelopers typically measure a Web application’s quality of service in terms of response time, throughput, and availability. Poor QoS translates into frustrated customers, which can lead to lost business opportunities. At the same time, company expenditures on a Web site’s IT infrastructure are a function of the site’s expected traffic. Ideally, you want to spend enough, and no more, allocating resources where they’ll generate the most benefit. For example, you shouldn’t upgrade your Web servers if customers experience most delays in the database server or load balancer. Thus, to maximize your ROI, you must determine when and how to upgrade IT infrastructure. One way to assess IT infrastructure performance is through load testing, which lets you assess how your Web site supports its expected workload by running a specified set of scripts that emulate customer behavior at different load levels. Here, I describe the QoS factors load testing addresses, how to conduct load testing, and how it addresses business needs at several requirement levels.