BookInfo is an open source application used by the Istio community to test and demonstrate various Istio features. A community of developers maintains it at https://github.com/istio/istio. The sample application represents a mix of programming languages so that we can realize the benefits of Service Mesh in later chapters. 

Importantly, we don't need to make any changes in the application code to provide routing, telemetry, and policy enforcement. Think of this as a DevOps environment in which no coding is required to implement operations, which typically requires instrumentation within the application itself. Today, this is a shift in application development, and Operations can fulfill its task without making any changes to the application.