Backend for frontend (or BFF for short) services, as the name suggests, are the backend services that provide accessible APIs for a Frontend Service. They are responsible for providing the data and functionality that the frontend services need to present to the user. They are also responsible for translating requests from the frontend services into requests to the Business Services.
Business services are the innermost layer of the Layered Service Architecture. They are responsible for providing the core business functionality, also known as Domain Logic, of the system. They are the only layer that is allowed to interact directly with the Event Stream.
Frontend services are the outermost layer of the Layered Service Architecture. They are the entry point for all user interactions with the system. They are responsible for presenting the user with a user interface, and for translating user actions into requests to the Backend for Frontend (BFF) services.
Layered Architecture separates components of a system into "layers", where each layer has a specific responsibility. This pattern is used to structure all our services. From the user's perspective, the layers from the outermost to innermost are Frontend, Backend-for-Frontend, and Business, as depicted in the following diagram:
Service Architecture refers to the infrastructure principles, patterns and best practices we use in deployed services. It is a set of guidelines that we follow to ensure that our services are well designed, easy to maintain and easy to extend.