The entire intent of load balancing is to balance the incoming network or application traffic across many physical servers—and make those servers look like one server to the outside world. There are many reasons to do this, but the primary drivers are the need for "scalability," "high availability," and "predictability."

Scalability is the capability of dynamically, or easily, adapting to increased load without impacting existing performance. High availability (HA) on the other hand, is the capability of a site to remain available and accessible even during the failure of one or more systems. Service virtualization (imitating the behavior of software components to accelerate and test application development) presents an interesting opportunity for both scalability and availability. If the service or point of user contact is separated from the actual servers, the application can be scaled by adding more servers. Moreover, the failure of an individual server will not render the entire application unavailable. Predictability is a little less clear as it represents pieces of HA as well as some lessons learned along the way. It can best be described as having control on how and when the services are being delivered with regard to availability and performance.

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