The Azure IoT Edge runtime is what turns a device into an IoT Edge device. The runtime can be deployed on devices as small as a Raspberry Pi or as large as an industrial server.
The IoT Edge security daemon provides and maintains security standards on the IoT Edge device. The daemon starts on every boot and bootstraps the device by starting the rest of the IoT Edge runtime.
Reference:
https://docs.microsoft.com/en-us/azure/iot-edge/how-to-install-iot-edge

An enrollment is the record of devices or groups of devices that may register through auto-provisioning. The enrollment record contains information about the device or group of devices, including:
* the attestation mechanism used by the device
* the optional initial desired configuration
* desired IoT hub
the desired device ID
Note: Azure IoT auto-provisioning can be broken into three phases:
1. Service configuration - a one-time configuration of the Azure IoT Hub and IoT Hub Device Provisioning Service instances, establishing them and creating linkage between them.
2. Device enrollment - the process of making the Device Provisioning Service instance aware of the devices that will attempt to register in the future. Enrollment is accomplished by configuring device identity information in the provisioning service, as either an "individual enrollment" for a single device, or a "group enrollment" for multiple devices.
3. Device registration and configuration
Reference:
https://docs.microsoft.com/en-us/azure/iot-dps/concepts-service#enrollment

IoT Hub provides three options for device apps to expose functionality to a back-end app:
* Twin's desired properties for long-running commands intended to put the device into a certain desired state.
For example, set the telemetry send interval to 30 minutes.
* Direct methods for communications that require immediate confirmation of the result. Direct methods are often used for interactive control of devices such as turning on a fan.
* Cloud-to-device messages for one-way notifications to the device app.
Reference:
https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-c2d-guidance Implement Edge Question Set 1

Each device uses its derived device key with your unique registration ID to perform symmetric key attestation with the enrollment during provisioning. To generate the device key, use the key you copied from your DPS enrollment to compute an HMAC-SHA256 of the unique registration ID for the device and convert the result into Base64 format.
Reference:
https://docs.microsoft.com/en-us/azure/iot-edge/how-to-auto-provision-symmetric-keys

Scenario: You discover connectivity issues between the IoT gateway devices and iothub1, which cause IoT devices to lose connectivity and messages.
To log device connection events and errors, turn on diagnostics for IoT Hub. We recommend turning on these logs as early as possible, because if diagnostic logs aren't enabled, when device disconnects occur, you won't have any information to troubleshoot the problem with.
Step 1:
1. Sign in to the Azure portal.
2. Browse to your IoT hub.
3. Select Diagnostics settings.
4. Select Turn on diagnostics.
5. Enable Connections logs to be collected.
6. For easier analysis, turn on Send to Log Analytics (see pricing).
Step 2:
Set up alerts for device disconnect at scale
To get alerts when devices disconnect, configure alerts on the Connected devices (preview) metric.
Reference:
https://docs.microsoft.com/bs-cyrl-ba/azure/iot-hub/iot-hub-troubleshoot-connectivity