Public MQTT Brokers

Cloud Based Implementation of IoT Using MQTT Brokers

This is a useful article that sums up the various MQTT options.

https://www.opensourceforu.com/2020/10/cloud-based-implementation-of-iot-using-mqtt-brokers/

When using public brokers, it is advised to consider encrypting traffic as standard. Both topics and payloads can be encrypted, with Node-RED providing nodes for such operations. Only devices that have the encryption key can find (subscribe) and make sense of the data.

The interesting question to ask is if public brokers are as good as a dedicated private broker.

Using public brokers has the following advantages:

A central list can be maintained (the table below can be loaded into software from this site)
With three or more brokers reliably available, one can establish primary and secondary routes, adding resilience and making for increased reliability
No maintenance, and no costs. A completely free approach to communications.
Data can be encrypted.
It is possible to share data by providing someone with encryption keys that lets them subscribe to data.

Node-RED MQTT Automation

Node-RED version 2 now allows one to manage MQTT subscriptions at run time through software, allowing the processes of encryption and subscribing to be automated.