Utility to download a copy of DeviceShadow

Short summary:

On startup, grab and save a copy of the default DeviceShadow info, as a JSON format file. Then subscribe to the update topic. Any time there is an update, refresh the copied file.

There are two versions of code. One is in the Greengrass directory, and the other is in the IoT directory. You probably want the IoT version.

Make a shadow first!!

Note that this code does NOT create a deviceshadow. Before using it, you need to create one, or it will error out. One way of doing this is through the GUI. Go to IoT -> All Devices -> Things Click on your device, then go to the Device Shadows tab. Then just click the "Create Shadow" button, and select Unnamed (classic) Shadow

Greengrass directory version

This version of the code uses the AWS Greengrass client related libraries, and thus will not work unless it has a properly functional Greengrass instance running on the same machine. It also expects to run as a "local" component. (See the make target for "localdeploy") Convert it to run from S3 yourself

IoT directory version

The code in the IoT directory can be run as a completely standalone AWS IoT client. For development convenience, it does expect to find its configuration in greengrass style, but it does NOT need a running greengrass instance to fuction. You can call it directly, with

sudo python3 iot.py

However, you have the option of running it as a local greengrass component instead. You can do that with

make localdeploy

Again, it should be easily possible to make it a standard S3 loaded component, but you currently have to do that yourself

Recap of why greengrass == bad

Using ShadowManager gives us the "benefit" of an AWS module that takes care of auto-syncing the cloud shadow to the local device. It also gives us the ability to keep "local shadows" that may or may not be synced to the cloud.

The problems are:

We dont need local-only shadows, so theres a lot of complexity we dont need
We are forced to keep accessing the shadow info through the HORRIBLE greengrass APIs
The additional required configuration and setup is a nightmare. THREE LAYERS OF REQUIRED ADDITIONAL CONFIG, to get through Greengrass access controls.. just to make ONE call!