Another typical communication method for IoT is the use of a publish subscribe bus, where the IoT devices push information as a stream. These buses are hosted on the cloud and you can use them to build your own services on top of them.

Conceptually, it is not too different from how Firebase Realtime Database works. It is a bit more structured, since it follows a well- known architecture pattern.

There are several companies that offer this service, but the most well-known ones are Google's Cloud Pub/Sub and PubNub.

Both are based on the same concepts: the IoT device registers with the service, opens a channel with publishing permission, and then it publishes the sensor updates to it while other services will subscribe to this channel, read the updates, and maybe decide to act on it.

You can also have the IoT device subscribe to its own channel (or stream) and get notifications when it is required to act on some event, or you can configure a separate channel for that.

Publish subscribe buses are complex, full of features, and also beyond the scope of this book. To learn more about them, you can check the official pages:

• Google Cloud Pub/Sub: https://cloud.google.com/pubsub/
• PubNub: https://www.pubnub.com/