MQTT
MQTT (Messaging Queueing Telemetry Transport) is a publish-subscribe protocol that helps bridge communications between disparate applications. In short, you can use it to send a message from one application to another.
Installing an MQTT Broker
A broker is required to serve as the "hub" for server/client connections.
We can use mosquitto for this:
$ sudo apt install mosquitto mosquitto-clients
Configuring MQTT Broker
Stop the Service First
$ sudo systemctl stop mosquitto.service
OR
$ sudo /etc/init.d/mosquitto stop
Configure the Service
Edit the configuration file (default location below):
$ sudo nano /etc/mosquitto/mosquitto.conf
Example configuration:
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example
pid_file /var/run/mosquitto.pid
persistence true
persistence_location /var/lib/mosquitto/
log_dest file /var/log/mosquitto/mosquitto.log
log_type error
log_type warning
log_type notice
log_type information
connection_messages true
log_timestamp true
include_dir /etc/mosquitto/conf.d
Restart the MQTT Service
$ sudo systemctl start mosquitto.service
OR
$ sudo /etc/init.d/mosquitto start
Testing the MQTT Broker
You can test the publish/subscribe handshake before setting up any channels to confirm your configuration is good. Do that like this:
- Open two terminal windows (or two ssh sessions)
- In one terminal, do:
$ mosquitto_sub -d -t hello/world- _sub = subscribe (or listen) for messages
- -d = debug the output
- -t = which thread (channel) to listen on
- hello/world = the name of the thread (channel) to communicate over
- In the second terminal, do:
$ mosquitto_pub -d -t hello/world -m "Test Message"- -m = tell mosquitto to send a message
- "Test Message" = the content of the message we're sending
- If all is well you should see the "Test Message" text appear in the first terminal window
Setting a Password
Defining a username & password for the client(s) that want to connect to the service is a no-brainer. Do that like so:
$ sudo mosquitto_passwd -c /etc/mosquitto/passwd <username>
This will let you specify a username. Set it to anything you want (e.g. mosquittousr) then run the command. The terminal will automatically ask ou to create a password (store this somewhere safe).
You can disable anonymouse connections to the service by doing the following:
- Edit the mosquitto config file at:
$ sudo nano /etc/mosquitto/conf.d/default.conf - Add these lines:
allow_anonymous false password_file /etc/mosquitto/passwd - Restart the mosquitto service:
$ sudo systemctl restart mosquitto.service