Flexibility is the hallmark of a service-oriented architecture, in which reusable application components can be shared across an enterprise and assembled in a loosely coupled way. In the data center, however, SOA technology's flexibility translates into unpredictability - a trait that is incompatible with traditional infrastructure technologies.

What if a particular Web service's workload skyrockets because two, five or 10 heavily used applications suddenly start calling the service? Meeting that demand requires being able to allocate computing resources on the fly. "You better have the capacity to support that one service and have planned for that scaling from an infrastructure perspective -- hardware, software, network, bandwidth and storage," says Donna Scott, an analyst at Gartner.