Since you have been using AWS IoT Core, I would recommend that you stay in fully managed services provided by AWS IoT suite. No need to reinvent the wheel such as provisioning a separate database for a basic requirement of pretty much every IoT-enabled solution.
What I understand is that you want to monitor your IoT device fleets for state changes or failures in operation, and to trigger actions when such events occur. To address this challenge, I’d suggest using AWS IoT Events. It accepts inputs from many different IoT telemetry data sources including smart sensors, edge devices, management applications, and other AWS IoT services. You can easily push any telemetry data input to AWS IoT Events by using a standard API interface.
In specific to device heartbeat, please take a look at this sample detector model. A detector model simply represents your equipment or process. On the console, you can find some other pre-made detector model templates which you can customize based on your use-case.
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