AZ-204 Question #61: Real Exam Question with Answer & Explanation

Question

Drag and Drop Question You develop an IoT solution by using Node.js. The solution is ready to deploy to the production environment. You must implement the device twin capabilities of Azure IoT Hub. You must register a sensor named Sensor00. The IoT Hub name is Hub01. You need to register the endpoint with ContosoHub01 so that you can configure them from your solution. Which four commands should you use to develop the solution? To answer, move the appropriate commands from the list of commands to the answer area and arrange them in the correct order. Answer:

Explanation

Azure IoT Hub Device Twin Registration — Explanation

Overview

This question asks you to set up a device twin in Azure IoT Hub using the Azure CLI and Node.js SDK. The correct four commands form a logical sequence: extend the CLI → register the device → get the device connection string → install the server-side SDK.

Step-by-Step Breakdown

1. az extension add --name azure-cli-iot-ext

The Azure CLI does not include IoT commands by default. This extension must be installed first or all subsequent az iot commands will fail with "command not found." This is always the prerequisite step.

Common mistake: Skipping this step and jumping straight to device creation — the CLI won't recognize az iot hub device-identity without the extension.

2. az iot hub device-identity create --hub-name (Hub01) --device-id Sensor00

This registers the device (Sensor00) in IoT Hub (Hub01), creating its device identity and twin. You cannot retrieve a connection string for a device that doesn't exist yet, so creation must come before querying.

Common mistake: Confusing --hub-name with --name. The device-identity subcommand uses --hub-name.

3. az iot hub device-identity show-connection-string --hub-name (Hub01) --device-id Sensor00 --output table

After the device is registered, you retrieve its device-specific connection string. This string is what the physical device (or simulator) uses to authenticate to IoT Hub. The question says you need to "register the endpoint with ContosoHub01 so you can configure them from your solution" — this connection string is that endpoint.

Common mistake: Using az iot hub show-connection-string --name (Hub01) instead. That retrieves the hub-level connection string (for backend services), not the device-level one. The device needs its own credentials.

4. npm install azure-iot-hub --save

The azure-iot-hub package is the service SDK — used by your Node.js backend to interact with device twins (read/write desired/reported properties). This is the correct package for the server side of a device twin solution.

Common mistake: Choosing npm install azure-iot-device azure-iot-device-mqtt --save instead. Those packages are for the device side (code running on the sensor itself), not for the backend solution managing twins. Since the question says "configure them from your solution," you need the service SDK.

Why the Other Items Are Wrong

Key Concept

Device twins require two connection strings: one for the hub (service SDK, backend) and one for the device (device SDK, sensor). This question focuses on the backend management flow, hence azure-iot-hub is the right npm package.

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