AWS IoT Device Shadow service Service - Internet of Things (IoT) Lens

AWS IoT Device Shadow service Service

AWS provides a feature called AWS IoT Device Shadow services to implement command and control over MQTT using these best practices. The Device Shadow has several benefits over using standard MQTT topics, such as a clientToken, to track the origin of a request, version numbers for managing conflict resolution, and the ability to store commands in the cloud in the event that a device is offline and unable to receive the command when it is issued. The device's shadow is commonly used in cases where a command needs to be persisted in the cloud even if the device is currently not online. When the device is back online, the device requests the latest shadow information and executes the command.

IoT solutions that use the Device Shadow service in AWS IoT Core manage command requests in a reliable, scalable, and straightforward fashion. The Device Shadow service follows a prescriptive approach to both the management of device-related state and how the state changes are communicated. This approach describes how the Device Shadows service uses a JSON document to store a device's current state, desired future state, and the difference between current and desired states.

Using Device Shadow with devices

Using Device Shadow with devices

  1. The device should check its desired state as soon as it comes online by subscribing to the $aws/things/<<thingName>>/shadow/name/<<shadowName>>/get topic. A device reports initial device state by publishing that state as a message to the update topic $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update.

  2. The Device Shadow reads the message from the topic and records the device state in a persistent data store.

  3. A device subscribes to the delta messaging topic $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update/delta upon which device-related state change messages will arrive.

  4. A component of the solution publishes a desired state message to the topic $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update and the Device Shadow tracking this device records the desired device state in a persistent data store.

  5. The Device Shadow publishes a delta message to the topic $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update/delta, and the Message Broker sends the message to the device.

  6. A device receives the delta message and performs the desired state changes.

  7. A device publishes an acknowledgment message reflecting the new state to the update topic $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update and the Device Shadow tracking this device records the new state in a persistent data store.

  8. The Device Shadow publishes a message to the $aws/things/<<thingName>>/shadow/name/<<shadowName>>/update/accepted topic.

  9. A component of the solution can now request the updated state from the Device Shadow.

    AWS IoT Device Management Jobs for device commands

In addition to the features described above for device commands, customers can also use AWS IoT Jobs to create a command pipeline, where the device infers the command from the payload of the MQTT message, as opposed to the topic. This enables customers to perform new kinds of remote operations with minimal device-side code changes. You can control the rate of roll-outs using Jobs, and provide abort / retry / timeout criteria to further customize the behavior of the job. AWS IoT Jobs integrates with Fleet Indexing and Thing Groups, which allows you to search your fleet and target devices in your fleet that meet specific criteria. With Job Templates, you can pre-define device-commands and create a library of reusable commands with just a few clicks on the target of your choice.