networks//network protocols//MQTT//MQTT broker

The MQTT broker is the intermediary of MQTT: it receives every publication and forwards it to the clients subscribed to the matching topic. It is the component that makes producers and consumers independent of each other (publish-subscribe).

The MQTT broker is the intermediary of MQTT: it receives every publication and forwards it to the clients subscribed to the matching topic. It is the component that makes producers and consumers independent of each other (publish-subscribe).

Several deployment options coexist: a broker on premises next to the plant, a hosted broker in the cloud, a hybrid with bridges between them, and redundant brokers for availability. A drawing of several servers behind one name is that redundancy. The choice between hosted and on premises is about who holds the data more than about cost: whoever runs the broker sees every message of the plant.

In a factory the broker is the fan-out point: a PLC gateway publishes once, and SCADA, MES, a historian, analytics and the cloud each subscribe (MQTT). A broker removes the coupling between producers and consumers and adds a dependency in its place: if it stops, every consumer stops at once, so a plant broker is clustered, monitored and patched like any other critical server. Store-and-forward on the publishing side and persistent sessions on the broker cover the moments the link is down.