MQTT topic to receive configuration updates

[Stanislav Lvovich]

Could you explain how to subscribe to updates of shadow configuration
using the account device (from an external cloud connected to MQTT) 

I have tried to use the root topic 
But i receive `shadow.desire` updates sent from UI ( /{deviceId}/shadow/update/delta )
Hot to get `shadow.ported` updates ?

[Markus Tacker (he/him)]

You can subscribe to `/{deviceId}/shadow/update/documents`.

[Stanislav Lvovich]

Hi, thank you for your reply

Do you mean {nrfcloud_mqtt_topic_prefix}/{deviceId}/shadow/update/documents` , right?

I have tried to subscribe to root topic {nrfcloud_mqtt_topic_prefix} and did not see any updates from shadow/update/documents

I'm connecting to the MQTT by the common device account client

[Markus Tacker (he/him)]

No. The shadow-documents are per-device, and you can only subscribe to the device-shadow topics from the device you are connecting as. 

This means the account cannot subscribe to AWS IoT shadow topics from other devices.

[Stanislav Lvovich]

So, maybe there is another way to understand a device has updated a config?

For example,
- the customer backend is updating `device.config` (shadow.config), using the nRF REST API method
- the device will update its config when online
- The customer backend wants to know when it happens (to update UI or else)

[Markus Tacker (he/him)]

Right now the only way to know when a regular device has updated its shadow is to poll the REST endpoint `FetchDevice`.

[Stanislav Lvovich]

maybe we can use /c2a topic?
I have seen some device state updates in this topic

[Markus Tacker (he/him)]

I am not aware that device shadow updates are republished right now.

[Lincoln Thomas]

We do indeed republish shadow updates to topics that an account device can subscribe to.

We will add this to our user documentation.

AWS topic	Republished to	Notes
$aws/things/{deviceId}/shadow/get/accepted	prod/{tenantId}/{deviceId}/shadow/get/accepted	tenantId (a.k.a. team) example: af793762-9bfc-48a8-80e9-53344754eb03 deviceId example: nrf-12345
$aws/things/{deviceId}/shadow/update/delta	prod/{tenantId}/{deviceId}/shadow/update/delta
$aws/things/{deviceId}/shadow/update/documents	prod/{tenantId}/devices/{deviceId}/c2a	Note: "/devices/" in this path, which is not in the other paths above

See https://docs.aws.amazon.com/iot/latest/developerguide/device-shadow-mqtt.html for details on what these AWS topics contain.