mosquitto.md

Mosquitto

Mosquitto is the message broker. Services such as the stack modules can publish messages to topics managed by the broker. They can also subscribe to topics.

All messages are exchanged with the MQTT protocol, which is similar to TCP but more lightweight.

The MQTT broker is the backbone of all communications within the stack

As we saw above, the broker container is running:

docker compose ps | grep mosquitto

stack-mosquitto-1     "/docker-entrypoint.…"   mosquitto           running             0.0.0.0:1884->1883/tcp

The mosquitto port in the container, 1883, is mapped to port 1884 on the host machine.

The mosquitto container runs the mosquitto server, and features a command line mosquitto client, mosquitto_sub

We'll run this client from within the container to connect to all topics:

docker exec stack-mosquitto-1 mosquitto_sub -v -t /#

You should see the messages that are being sent by the dummy modules:

/lv/status [{"number": 0, "on": 0, "vreq": 0.0}]
/hv/status [{"number": 0, "on": 0, "vreq": 0.0}]
/sensor_1/status {"meas1": -0.9931889975255942, "meas2": 0.9931889975255942}

You can also submit messages with mosquitto_pub. For help, do:

docker exec stack-mosquitto-1 mosquitto_pub --help