Web APIs

A Web API is a set of functions and procedures that allow for the creation of applications that access the features or data of an operating system, application, or other service.

Client Scenarios

Single Client - Same Organization Boundary

• High coordination between client and HTTP API;
• Easy to add and coordinate changes on both the client and the API;
• Short-lived: months;
• Data-oriented;
• Provides data for clients to use on their own ways.

Multiple Clients - Different Organization Boundaries

• Difficult to coordinate changes on both the clients and the APIs;
• Long-lived: years, decades;
• Journey-oriented (process-oriented);
• Exposes functionality for clients to provide very well defined journeys/processes.
• Hypermedia is a way to reduce coupling between clients and a specific HTTP API implementation.

System Architecture

• Backend:

  • Service responsible to ensure data integrity, namely that all domain rules are respected - business logic;
  • Server-side.

• Frontend:

  • Responsible for the user interaction;
  • Client-side.

The interaction between the frontend and the backend is done through an HTTP API, provided by the backend service:

• The communication initiative is always on the API’s client;
• The backend service only communicates information to the frontend service in the context of an HTTP response;
• Implies polling by the frontend application to check for asynchronous state changes.

Backend Service Architecture

• A DBMS (Database Management System), holding the system state/data;
• One or more servers, running an application, hosting the HTTP request handling logic, domain logic, and data access logic;
• Load-Balancer, to distribute the load across multiple servers:

API Design

• Handler:
  • Knows how to handle a request;
  • Knows how to serialize and deserialize the request and response;
  • Knows HTTP;
  • Does not know business logic;
• Service;
  • Contains the business logic;
  • Does not know HTTP;
  • Does not know how to interact with the database;
• Repository;
  • Knows how to interact with the database;
  • Does not know business logic;
• Data Access (DBMS);
  • Knows how to interact with the database;
  • Does not know business logic.