This last practice is about learning all about how your application is doing in production. Gathering metrics such as response times and the number of requests will tell you about how the systems are performing. Capturing errors is also part of performance monitoring and allows you to start fixing problems without having to wait on your customers to contact you about them.

In addition to that, you can gather information on which parts of the application are more or less frequently used and whether new features are being picked up by users. Learning about usage patterns provides you with great insights into how customers really use your applications and common scenarios they are going through.

Chapter 9, Security and Compliance, and Chapter 10, Application Monitoring, will go into detail on learning about both your application and your users' behavior in production.