IoT thing shadow and Greengrass component

Hi lacteolus,

The device SDK provides clients and APIs for accessing the AWS IoT cloud data plane services. It also provides a client for talking with the Greengrass v2 IPC.

The IoTShadowClient in the device SDK is a client for talking directly with the AWS IoT Device Shadow Service in the cloud.
It maintains its own connection - hence the need for the device certificate information. This client does not work through the Greengrass IPC.

At this time, there is no equivalent to the local shadow service / sync that Greengrass v1 provides.

In order to talk to the cloud shadow service, you do not need to use the IoT shadow client. A V2 component can talk with IoT Shadow via the Greengrass managed MQTT connection.

The following access control policy allows your component to subscribe and publish to the shadow MQTT topics

      "accessControl": {
        "aws.greengrass.ipc.mqttproxy": {
          "shadow-mqtt-example": {
            "policyDescription": "Allows access to shadow.",
            "operations": [
              "*"
            ],
            "resources": [
              "$aws/things/+/shadow/#"
            ]
          }
        }
      }

Your python component can follow the MQTT pub/sub example here: https://docs.aws.amazon.com/greengrass/v2/developerguide/ipc-iot-core-mqtt.html

You can subscribe to $aws/things/thingName/shadow/update/accepted to get any remote shadow updates
and publish state to $aws/things/thingName/shadow/update

In this case, thingName is the name of the thing you want to update.

You can use the environment variable $AWS_IOT_THING_NAME to use the thing name of the core device

See https://docs.aws.amazon.com/iot/latest/developerguide/device-shadow-mqtt.html for more detail about using the shadow MQTT topics.

Edited by: rob-aws on Mar 8, 2021 11:05 AM

Hi rob-aws,
Thanks for info. So it means that we need to implement something similar to IoTShadowClient but using IPC and subscriptions to all needed shadow topics (update, delta, get etc.).
I looked at https://github.com/aws/aws-iot-device-sdk-python-v2/blob/main/samples/shadow.py example and it seemed to be convenient - it has special classes for different shadow requests and methods for publishing and subscribing to named and classis shadow topice etc.