Node-RED communications protocols

Julian Knight — Thu, 20 Aug 2020 17:53:20 +0000

Node-RED has an excellent choice of communications protocols available to it. This article looks at the main options and their strengths and weaknesses. It also gives suggestions as to when you may wish to use them.

Node-RED is renown for its MQTT support since that is where it started - as an IBM demonstrator for their experteese on IoT.

However, this is only one of many ways to send/receive data between Node-RED and other systems or services. Each of tese protocols has its own advantages and disadvantages.

The protocols

In rough order of descending order of ease of use (very rough!):

MQTT
Websocket
HTTP
TCP
UDP
UNIX Pipes

MQTT

This is likely to be the easiest to use even though it requires an extra service to be running, a “Broker”.

There is even a custom node available that lets you run a broker from within Node-RED itself. However, I don’t recommend doing that because it adds significant overheads that are easily avoided. The most commonly used broker is “Mosquito” which has low resource overheads, is fast, secure and capable. It is easily installed and configured.

While MQTT data payloads are just strings, Node-RED lets you send and receive more complex data structures (JSON).

The things that put MQTT at the top of the list are:

The ability to easily handle more complex data
The availability of MQTT libraries and clients for many platforms

Websocket

HTTP

TCP

UDP

UNIX Pipes

Mosquitto MQTT Server on a Raspberry Pi

Julian Knight — Sun, 29 Nov 2015 23:10:53 +0000

To access an MQTT broker direct from the browser, you need websockets support. On a Raspberry Pi, this used to require a custom build from source. That is no longer required. You can now install direct from the mosquitto.org repository and add a simple config change. This article explains the details.

MQTT is a messaging protocol for the “Internet of Things” (IoT). It allows devices to communicate easily with minimal overheads. The Raspberry Pi of course makes an excellent low cost platform for managing IoT. Not only is it cheap to buy, it is also cheap to keep running.

To use MQTT, you need a “broker” which is simply a service running in the background. Mosquitto is one of the more popular brokers, partly because it is pretty small and therefore ideal for running on a Pi.

If you want to use MQTT from the browser however, you also need the broker to support something called “websockets” since browsers cannot directly talk using the MQTT protocol. In the past, Mosquitto didn’t have websockets compiled in by default and compiling your own version on a Pi is painful to say the least.

Thankfully, this is no longer a problem since the authors of Mosquitto now provide a repository containing ARM versions which work fine on the Pi. See mosquitto.org for the details.

Once installed from the repository, you will need to add a suitable configuration since websockets are not part of the default configuration.

To turn it on, you should add a new file to /etc/mosquitto/conf.d/ containing something like:

# See: http://mm011106.github.io/reference/mosquitto_conf.html
# Standard Listener
listener 1883
protocol mqtt
allow_anonymous false
password_file /etc/mosquitto/passwords.txt
# Websockets Listener
listener 9001
http_dir
Set the protocol to accept for this listener. Can be mqtt (the default), or websockets.
protocol websockets

Note that you can create more than one listener of the same type. You might, for example, want to create another listener that is restricted to a subset of topics so that you can allow access to that over the Internet. Perhaps you would restrict it to listing only sensor data but not control messages for your home automation project for example.

Once you have enabled websockets access to Mosquitto, you can do some interesting things directly from web pages. Get hold of MQTT.js for the browser and you can both listen to and send messages from/to the broker. Combined with a framework such as REACT allows you to, with only a few lines of code, display all the messages that arrive at your broker.

Updated 2018-04-24 21:20:16 - Tidy output after migration from WordPress.

MQTT on Much Ado About IT