如果AWS IoT中没有Device Shadows概念，会发生什么

Question

I am trying to work on AWS IoT.. From my understanding aws shadow copy the state information of the device/thing.. but i don't understand why.. what happen if its not stored any device state information ?? I will be happy if anyone explains with simple example

Answer 1

Device shadow is basically a copy of state of your device in the cloud. What it allows you to do is to make state changes on the device even when the device is disconnected from the network. Those changes are made on its shadow and once the device reconnects with cloud, states of the device and the shadow are synchronized.

Suppose that you have a smart lightbulb which is currently on. You configured your system in such a way that the lightbulb should be turned off at 6am but there is network outage at 5:55am which lasts for 10 minutes. If you are not using device shadow, then the state change will try to reach your lightbulb but since it is disconnected at that particular time, the message is lost and your lightbulb will not be turned off.

If you are using device shadow, this state change is performed on it so the shadow lightbulb will be turned off at 6am even if the real one is not connected to the cloud. When the lightbulb is reconnected at 6:05am, device shadow sends synchronization message to it and it will be turned off.

If you could ensure that your devices are always connected to the cloud, which you can't because networks are inherently unreliable, then using device shadow would be pointless. Bottom line is that it allows you to perform offline state management with automatic synchronization.