MQTTBroker

An MQTT broker is a server that implements the Message Queuing Telemetry Transport (MQTT) protocol and serves as the central hub for message routing in MQTT-based networks. It accepts connections from MQTT clients, manages sessions, subscriptions, and authentication, and routes published messages to subscribing clients. The broker decouples publishers and subscribers, enabling scalable, asynchronous communication in IoT and other event-driven applications.

In operation, clients connect to the broker and can publish to topics or subscribe to topics. The broker matches published messages against active subscriptions using topic filters and delivers messages according to the requested quality of service (QoS 0, 1, or 2). It may also store retained messages, implement last-will messages, and support persistent sessions so clients can reconnect and resume state after disconnection. Topics form a hierarchical namespace with wildcards used in subscriptions.

Brokers provide features for security, reliability, and scale, including TLS transport, authentication, access control lists, message persistence, bridging to other brokers, and clustering for high availability. They can operate in edge, gateway, or cloud deployments and support bulk messaging, offline buffering, and message durability.

Common MQTT broker implementations include open-source options such as Eclipse Mosquitto, EMQX, and RabbitMQ with MQTT plugin, as well as commercial products like HiveMQ. These brokers vary in performance, clustering capabilities, and management tools, but all share the core role of routing MQTT messages between clients. The term MQTTBroker is commonly used informally to refer to broker software implementing MQTT, and is not a formal product name.