Fundamental Book on API Development and Implementation. The basic issues of information exchange in the microservice architecture, processing requests on sites and in web applications (REST paradigm) are analyzed. It shows how to progressively develop existing APIs without rewriting them, as well as how to create an API of any complexity from scratch, taking into account the capabilities and limitations of a particular system. The book will help to implement the service network architecture in the enterprise and prepare the company's resources for migration to the cloud.