The broker will act as an intermediary between OpenMQTTGateway and your controller, it can be seen as a centralized hub at the heart of your automation system. It carry on messages following a publish / subscribe mechanism.
All the events or commands could pass by the broker.
There is many choice of brokers, here is some of the most populars:
- Mosquitto (Open source)
- Moquette (Open source)
- Embedded MQTT brokers (Home Assistant and OpenHAB)
Once your broker installed it can be interesting to see the traffic passing to it and to publish data, so as to do that there is several tools available: