Glossary · Industrial communication
MQTT broker
Also known as: MQTT server
German: MQTT-Broker
In MQTT, a broker (called the Server in the OASIS specification) is the central application that accepts client connections, receives published messages, matches their topics against the clients' subscriptions and forwards the messages, and that keeps retained messages, will messages and session state.
- Industrial communication
- Standards
In one sentence
An MQTT broker accepts client connections, matches published messages to subscriptions and keeps retained messages and session state.
Example
An MQTT broker at plant level receives the states of all six machines of a packaging line from their edge gateways and forwards them to the MES, the energy dashboard and a cloud connector.
How it applies
- Engineering: The broker is a single point that every message passes through. Plants plan it like any central system: sizing, clustering or a standby broker, and bridges between site and cloud brokers.
- Security: Authentication of clients, TLS and access rules per MQTT topic are broker settings. Without them anyone who reaches the broker can read everything and publish commands, so the broker belongs in a defined Security zone.
- Operations: The broker keeps Retained message (MQTT)s and the state of Persistent session (MQTT)s; its storage and limits (message size, queue length, session expiry) determine what survives outages and restarts.
- Documentation: The documentation team documents the broker addresses and ports, the authentication method, the access rules per topic, limits, bridging and the backup and failover behavior.
MQTT broker vs. message broker
An MQTT broker is a Message broker for one protocol with simple topic routing. General message brokers and event streaming platforms may add queues, persistent logs and several protocols; some of them also speak MQTT.