In the chapters so far, you have learned how to secure user-facing APIs from a variety of threats using security controls such as authentication, authorization, and rate-limiting. It’s increasingly common for applications to themselves be structured as a set of microservices, communicating with each other using internal APIs intended to be used by other microservices rather than directly by users. The example in figure 10.1 shows a set of microservices implementing a fictional web store. A single user-facing API provides an interface for a web application, and in turn, calls several backend microservices to handle stock checks, process payment card details, and arrange for products to be shipped once an order is placed.
Definition
A microservice is an independently deployed service that is a component of a larger application. Microservices are often contrasted with monoliths, where all the components of an application are bundled into a single deployed unit. Microservices communicate with each other using APIs over a protocol such as HTTP.