In practice, the performance of non-trivial applications is rarely a function of coincidence or prediction. For many projects, performance is not an option (it is rather a necessity), which is why this is even more important today. Capacity planning, determining performance objectives, performance modeling, measurement, and monitoring are key.

Tuning a poorly designed system to perform is significantly harder, if not practically impossible, than having a system well-designed from the start. In order to meet a performance goal, performance objectives should be known before the application is designed. The performance objectives are stated in terms of latency, throughput, resource utilization, and workload. These terms are discussed in the following section in this chapter.

The resource cost can be identified in terms of application scenarios, such as browsing of products, adding products to shopping cart, checkout, and more. Creating workload profiles that represent users performing various operations is usually helpful.

Performance modeling is a reality check for whether the application design will support the performance objectives. It includes performance objectives, application scenarios, constraints, measurements (benchmark results), workload objectives and if available, the performance baseline. It is not a replacement for measurement and load testing, rather, the model is validated using these. The performance model may include the performance test cases to assert the performance characteristics of the application scenarios.

Deploying an application to production almost always needs some form of capacity planning. It has to take into account the performance objectives for today and for the foreseeable future. It requires an idea of the application architecture, and an understanding of how the external factors translate into the internal workload. It also requires informed expectations about the responsiveness and the level of service to be provided by the system. Often, capacity planning is done early in a project to mitigate the risk of provisioning delays.