This chapter establishes the fundamental choice between synchronous and asynchronous communication and when each is appropriate.

This chapter covers REST constraints, HTTP semantics, the Richardson maturity model, and how to version APIs without breaking clients.

This chapter covers Protocol Buffers, gRPC streaming modes, and when to use gRPC over REST for internal service communication.

This chapter covers GraphQL schema design, the N+1 query problem, DataLoader batching, and when GraphQL is worth its complexity.

This chapter covers WebSockets, SSE, and long polling for real-time communication, with decision guidance on when to use each.

This chapter covers event-driven patterns, choreography vs orchestration, CQRS, and the outbox pattern for reliable event publishing.

This chapter covers idempotency, pagination, error handling, deprecation strategy, and security for APIs designed to last years.