Messaging Protocol

A messaging protocol defines the rules and message formats that let systems talk to each other asynchronously, moving data through queues, topics, and brokers instead of direct request/response calls. Where HTTP answers “give me this now,” a messaging protocol answers “deliver this when the consumer is ready.” Protocols like AMQP, MQTT, STOMP, and the Kafka wire protocol each make their own trade-offs around ordering, delivery guarantees, and connection overhead.

• Publish and subscribe - Producers emit messages to topics or queues without knowing which consumers, if any, will read them.
• Delivery guarantees - At-most-once, at-least-once, and exactly-once semantics are negotiated by the protocol, not left to the application.
• Brokered decoupling - A broker sits between systems so producers and consumers can scale, fail, and restart independently.
• Binary-efficient framing - Most of these protocols use compact binary framing to keep throughput high and latency low at scale.

In real API operations messaging protocols carry the event-driven half of most modern architectures, and their contracts are described with AsyncAPI the way REST is described with OpenAPI. Governing them well means treating a topic and its message schema as a first-class API surface — versioned, documented, and secured — which matters more than ever as agents subscribe to event streams to stay current rather than polling REST endpoints.