Which architectural design principle focuses on developing small services that communicate with lightweight APIs?

The architectural design principle that focuses on developing small services that communicate with lightweight APIs is Microservices Architecture. This approach divides applications into smaller, self-contained units, or microservices, each of which can be deployed and scaled independently. By leveraging lightweight APIs, microservices can communicate with each other seamlessly, allowing for greater flexibility, agility, and the ability to adopt diverse technologies as needed.

Microservices architecture contrasts with monolithic architecture, in which applications are built as a single, interconnected unit. This can lead to challenges in scaling and maintaining the application, as changes to one part of the code could impact the entire system.

While serverless architecture allows for deploying applications without managing server infrastructure, it doesn't specifically emphasize the use of small, independent services like microservices do. Event-driven architecture focuses on building systems that react to events, but it doesn't inherently describe the structure of the services or how they communicate.

Overall, microservices architecture is recognized for its effective use of APIs and its operational advantages in modern cloud environments, making it the correct choice in this context.