Connect a child IoT device to an IoT Edge gateway

15 minutes

This exercise will configure the downstream child IoT Devices to connect to IoT Hub using their configured Symmetric Keys. The devices will be configured to connect to IoT Hub and the parent IoT Edge Device using a Connection String containing the Symmetric Key and the Gateway Hostname for the Parent IoT Edge Device.

The process to authenticate regular IoT devices to IoT Hub with symmetric keys also applies to downstream (or child / leaf) devices. The noted difference is the added pointer to the Gateway Device to route the connection or, in offline scenarios, to handle the authentication on behalf of IoT Hub.

In a previous unit, you created the IoT Device Identities in Azure IoT Hub. You copied the Connection String for the IoT Device. The Connection String can also be accessed with the Azure portal for the Device ID of the device within Azure IoT Hub.

Connecting the child IoT device to IoT Edge gateway

Copy the azure-iot-test-only.root.ca.cert.pem x.509 certificate file downloaded previously (when the IoT Edge Gateway was configured) to the /LabFiles/ChildIoTDevice directory where the source code for the Child IoT Device is located.
Open the /LabFiles/ChildIoTDevice directory within Visual studio Code.
Open the ChildIoTDevice.cs source code file.
Locate the declaration for the s_connectionString variable and replace the value placeholder with the IoT Hub Connection String for the ChildDevice1 IoT Device.
Modify the IoT Hub Connection String to include the GatewayHostName property with the value set to the Hostname for the IoT Edge Gateway (IoTEdgeGateway) virtual machine.

The Connection String will match the following format:
```
    HostName=<iot-hub-name>.azure-devices.net;DeviceId=DownstreamDevice1;SharedAccessKey=<iot-device-key>;GatewayHostName=<iot-edge-gateway-hostname>
```
Be sure to replace the placeholders with the appropriate values:
- iot-hub-name: The Name of the Azure IoT Hub.
- iot-device-key: The Primary or Secondary Key for the ChildDevice1 IoT Device in IoT Hub.
- iot-edge-gateway-hostname: Enter the IP Address for the IoTEdgeGateway virtual machine.
Save the file.
Open the Terminal window within Visual Studio Code.
Navigate the Terminal to the location of the /LabFiles/ChildIoTDevice directory.
Run the following command to build the code for the ChildIoTDevice simulated device, and execute it to start sending device telemetry:
```
     dotnet run
```
When the app installed the x.509 certificate on the local machine so it can use it to authenticate with the IoT Edge Gateway, it may prompt asking if you would like to install the certificate. Click Yes to allow it and continue.

Once the simulated device is running, the console output will display the events being sent to the Azure IoT Edge Gateway.

The terminal output will look similar to the following example:

   IoT Hub Quickstarts #1 - Simulated device. Ctrl-C to exit.

    User configured CA certificate path: azure-iot-test-only.root.ca.cert.pem
    Attempting to install CA certificate: azure-iot-test-only.root.ca.cert.pem
    Successfully added certificate: azure-iot-test-only.root.ca.cert.pem
    11/27/2019 4:18:26 AM > Sending message: {"temperature":21.768769073192388,"humidity":79.89793652663843}
    11/27/2019 4:18:27 AM > Sending message: {"temperature":28.317862208149332,"humidity":73.60970909409677}
    11/27/2019 4:18:28 AM > Sending message: {"temperature":25.552859350830715,"humidity":72.7897707153064}
    11/27/2019 4:18:29 AM > Sending message: {"temperature":32.81164186439088,"humidity":72.6606041624493}

Leave the simulated device running while you move on to the next unit.

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Connecting the child IoT device to IoT Edge gateway

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