In this chapter, we had a look at MQTT—the IoT protocol—which we will use to build the projects in the hands-on part of this book. It is a lightweight protocol, which is especially suitable for the communication of restricted devices, either because of processing power, network bandwidth, or battery power, and therefore, it is a perfect fit for the projects that we are about to build.

MQTT is based on the publish and subscribe pattern. Each message is published to a topic, which can be compared to the categories in a newspaper. A subscriber can subscribe to this information in order to receive updates about it, "I only want to get updates on foreign affairs and cultural news, but don't care about sports."

We also learned that a single entity, the MQTT server, manages all of the communication between the clients, and is essential for the communication...