Today Fleet Hub and Fleet Indexing connectivity (FI) will only report for MQTT connections directly to AWS IoT Core. You should be able to see the Greengrass Core device connectivity status but will not be able to see the status of client devices that connect to the local MQTT broker. The reason for this is that FI uses the lifecycle events from IoT Core. There isn't a way for a Greengrass Core device to emit those events for client devices.
You could create a component that reads the Nucleus log file,
greengrass.log, and parse client device connect/disconnect events. Fleet Hub will not be able to report on those from a connectivity perspective, but you could update a custom attribute or shadow field with device status and then create a Fleet Hub query.
To track interest, please consider creating an issue for the Greengrass team to track a feature request.
Please let me know if this helps, or if you have additional questions!
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