Mosquitto is a message broker that implements the MQTT protocol. MQTT is very used in IOT to share info between devices. In this post we will simulate a communication between a subscriber (for example a wifi light bulb) and a publisher (a device invoking “turn on” or “turn off” the light)

Starting MQTT Server

Create the next docker-compose.yml file

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version: '2.1'
services:    
  mqtt:
    image: toke/mosquitto:latest
    ports:
        - 1883:1883
        - 9001:9001
    volumes:
    - ./log/mqtt:/mqtt/log
    - ./data/mqtt:/mqtt/data/
    #- ./config/mqtt:/mqtt/config

This will start the mosquitto server with the default options (port 1883). If you want configure other options, uncomment the last line of docker-compose and include in that directory a mosquitto.conf file. More info of this configuration here

Now, start the server with docker-compose up

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mqtt_1  | 1539943920: mosquitto version 1.4.15 (build date Sat, 07 Apr 2018 19:13:41 +0100) starting
mqtt_1  | 1539943920: Config loaded from /mqtt/config/mosquitto.conf.
mqtt_1  | 1539943920: Opening websockets listen socket on port 9001.
mqtt_1  | 1539943920: Opening ipv4 listen socket on port 1883.
mqtt_1  | 1539943920: Opening ipv6 listen socket on port 1883.

Install the MQTT Mosquitto client

• Mac brew install mosquitto

• Linux distributions with snap support snap install mosquitto

• Others Download

Subscribe to a topic

We can simulate that we have a wifi light bulb that is listening from a topic and depending on the value it will turn on or turn off. In this case we have:

• A topic /home/light/state
• The possibles values for this topic “ON” and “OFF”

For simulate this, we must open a new tab in our console and type:

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mosquitto_sub -t /home/light/state`

Now the subscriber will be listening all messages sent to the topic /home/light/state

Publish to the topic

Open a new tab in your console and type:

mosquitto_pub -t /home/light/state -m "ON" mosquitto_pub -t /home/light/state -m "OFF" mosquitto_pub -t /home/light/state -m "ON"

In the terminal of previous subscriber you will can see the receive values:

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➜  ~ mosquitto_sub -t topic/state
ON
OFF
ON

References

[1] Link to the project in Github