Hands-On Internet of Things with MQTT

Topic names

The topic name specifies where MQTT messages are sent to. Each MQTT server has its own topics, which can be freely defined on the fly by the publishers. Imagine a topic as a tree of categories. Each / defines a sub-category. So, when we look back at the topic name from the previous section, /living-room/my-custom-coffee-machine, we can see that the topic consists of two components:

• /living room
• /my-custom-coffee-machine

If, next to your custom smart coffee machine, you had another smart device in the living room, which communicates via MQTT, let's say a custom smart light, you could publish its information in the same /living-room root topic: /living-room/my-custom-smart-light.

Topic names are case-sensitive. So, /livingroom ...