Communicating over MQTT

MQTT

MQTT is a lightweight publish-subscribe protocol running over TCP. An MQTT broker handles client connections, as well as receiving and broadcasting messages.

Connect to an MQTT broker

Managed IoT Cloud leverages the MQTT broker in AWS IoT Core. It lets clients connect to it using:

• Client X.509 certificate
• Credentials from a login to MIC

If you are connecting to the MQTT broker as a physical device, use the Thing API. If you are connecting as a MIC user, use the Thing Update API.

Thing API

Physical devices communicate using client X.509 certificates over MQTT using the Thing API. A certificate grants access to publish and subscribe to data only for the thing it is provisioned for.

Make sure to follow our Payload Conventions to get the most out of MIC. The Invoke Service provides utility functions for things.

Available MQTT Topics include:

• Device Shadow MQTT topics for standard communication
  • $aws/things/<thingName>/...
• TCXN Topic Namespace (tcxn/things/...) for additional services like:
  • Backdating observations
  • Last Will and Testament (LWT)
  • Invoke Service
• Other
  • Public topic (public)

Thing Update API

MIC users communicate over MQTT using the Thing Update API with credentials from a MIC login. It is designed to let a MIC user subscribe and publish data to the things that it has been given access to. Users get access to things through the users roles which grants privileges to the domains the things belong to.

Available MQTT Topics include:

• Device Shadow updates
  • thing-update/<domainPath>/<thingName>
• Event topic
  • event/<domainPath>