To use the advantages of this stack, sensors and input devices are connected to MQTT because they can talk this by default. All the service and backend stuff has to be at Kafka. Some input devices can react to MQTT messages, also. So there is a need to send from backend services thrus Kafka to MQTT. Just do deal with MQTT as a lot of videos and tutorials with Node-Red here are telling - therefor use an easy MQTT broker and this stack would be overkill definitely. But as I read and you said: There is a reason for.