This book is a complete guide to designing and implementing scalable, secure, and modern APIs in a microservices architecture. Covering both synchronous communication via REST, GraphQL, and gRPC, as well as asynchronous communication with Kafka, it equips you with the tools to build efficient, reliable, and observable APIs.Learn best practices for designing REST APIs, including htp verb usage and the API-first approach. Explore Spring Boot technologies like WebFlux and virtual threads to build scalable REST APIs. The book also demonstrates how to use Spring Cloud Stream for broker-agnostic asynchronous communication to build robust event-driven architectures.To ensure observability, you will implement logging, monitoring, and tracing with Grafana, Prometheus, and Tempo. Security is key, and the book covers OAuth2 and OpenID Connect using Spring Security and Keycloak for centralized authentication. Finally, discover how to deploy microservices with Docker and Kubernetes, mastering containerization and orchestration.