Topics Overview (MQTT and Google PubSub)
- Akash Sharma
As MQTT clients, devices can publish to a limited set of MQTT topic patterns:
/devices/{deviceID}/state
/devices/{deviceID}/events/#
/devices/+/attach (for special devices called gateways only)
/devices/+/detach (for special devices called gateways only)
Devices cannot subscribe to any of the above topic patterns.
Devices can subscribe to a limited set of MQTT topic patterns:
/devices/{deviceID}/config
/devices/{deviceID}/commands/#
/devices/{deviceID}/errors
Devices cannot publish to any of the above topic patterns.
As MQTT clients, devices that wish to send data to ClearBlade IoT Core would publish either to /devices/{deviceID}/events/# or /devices/{deviceID}/state. In order for that data to be forwarded beyond ClearBlade IoT Core (e.g. to trigger Google Cloud Functions), the MQTT topics must be mapped to a different, non-MQTT messaging service called Google PubSub.
The following screenshot shows a registry where Google PubSub topics (not to be confused with MQTT topics) are configured:
What this shows us is…
If a device in this registry publishes messages to MQTT topic /devices/{deviceID}/events/mySubFolder then the data gets forwarded to Google PubSub topic projects/api-project-320446546234/topics/sub
If a device in this registry publishes messages to MQTT topic /devices/{deviceID}/events or /devices/{deviceID}/events/{anything_other_than_the_explicitly_mapped_subfolder} then the data gets forwarded to Google PubSub topic projects/api-project-320446546234/topics/rootevent
If a device in this registry publishes messages to MQTT topic /devices/{deviceID}/state then the data gets forwarded to projects/api-project-320446546234/topics/state
Learn about Google PubSub here.
Learn about Google Cloud Run Functions here.
Note: if devices need to communicate via HTTP instead of MQTT, they should use these APIs.