Get started with IoT Hub module identity and module twin (Node.js)

Module identities and module twins are similar to Azure IoT Hub device identity and device twin, but provide finer granularity. While Azure IoT Hub device identity and device twin enable the back-end application to configure a device and provides visibility on the device's conditions, a module identity and module twin provide these capabilities for individual components of a device. On capable devices with multiple components, such as operating system devices or firmware devices, it allows for isolated configuration and conditions for each component.

At the end of this article, you have two Node.js apps:

• CreateIdentities: creates a device identity, a module identity, and associated security keys to connect your device and module clients.

• UpdateModuleTwinReportedProperties: sends updated module twin, reported properties to your IoT Hub.

Prerequisites

• An IoT Hub. Create one with the CLI or the Azure portal.

• Node.js version 10.0.x or later. Prepare your development environment describes how to install Node.js for this article on either Windows or Linux.

Get the IoT hub connection string

In this article, you create a back-end service that adds a device in the identity registry and then adds a module to that device. Your service requires the registry write permission. By default, every IoT hub is created with a shared access policy named registryReadWrite that grants this permission.

To get the IoT Hub connection string for the registryReadWrite policy, follow these steps:

1. In the Azure portal, select Resource groups. Select the resource group where your hub is located, and then select your hub from the list of resources.

2. On the left-side pane of your hub, select Shared access policies.

3. From the list of policies, select the registryReadWrite policy.

4. Copy the Primary connection string and save the value.

   

For more information about IoT Hub shared access policies and permissions, see Access control and permissions.

Create a device identity and a module identity in IoT Hub

In this section, you create a Node.js app that creates a device identity and a module identity in the identity registry in your IoT hub. A device or module can't connect to IoT hub unless it has an entry in the identity registry. For more information, see Understand the identity registry in your IoT hub. When you run this console app, it generates a unique ID and key for both device and module. The ID and key are case-sensitive. Your device and module use these values to identify itself when it sends device-to-cloud messages to IoT Hub.

1. Create a directory to hold your code.

2. Inside of that directory, first run npm init -y to create an empty package.json with defaults. This is the project file for your code.

3. Run npm install -S azure-iothub@modules-preview to install the service SDK inside the node_modules subdirectory.

   Note

   The subdirectory name node_modules uses the word module to mean "a node library". The term here has nothing to do with IoT Hub modules.

4. Create the following .js file in your directory. Call it add.js. Copy and paste your hub connection string and hub name.

   var Registry = require('azure-iothub').Registry;
   var uuid = require('uuid');
   // Copy/paste your connection string and hub name here
   var serviceConnectionString = '<hub connection string from portal>';
   var hubName = '<hub name>.azure-devices.cn';
   // Create an instance of the IoTHub registry
   var registry = Registry.fromConnectionString(serviceConnectionString);
   // Insert your device ID and moduleId here.
   var deviceId = 'myFirstDevice';
   var moduleId = 'myFirstModule';
   // Create your device as a SAS authentication device
   var primaryKey = new Buffer(uuid.v4()).toString('base64');
   var secondaryKey = new Buffer(uuid.v4()).toString('base64');
   var deviceDescription = {
     deviceId: deviceId,
     status: 'enabled',
     authentication: {
       type: 'sas',
       symmetricKey: {
         primaryKey: primaryKey,
         secondaryKey: secondaryKey
       }
     }
   };
   
   // First, create a device identity
   registry.create(deviceDescription, function(err) {
     if (err) {
       console.log('Error creating device identity: ' + err);
       process.exit(1);
     }
     console.log('device connection string = "HostName=' + hubName + ';DeviceId=' + deviceId + ';SharedAccessKey=' + primaryKey + '"');
   
     // Then add a module to that device
     registry.addModule({ deviceId: deviceId, moduleId: moduleId }, function(err) {
       if (err) {
         console.log('Error creating module identity: ' + err);
         process.exit(1);
       }
   
       // Finally, retrieve the module details from the hub so we can construct the connection string
       registry.getModule(deviceId, moduleId, function(err, foundModule) {
         if (err) {
           console.log('Error getting module back from hub: ' + err);
           process.exit(1);
         }
         console.log('module connection string = "HostName=' + hubName + ';DeviceId=' + foundModule.deviceId + ';ModuleId='+foundModule.moduleId+';SharedAccessKey=' + foundModule.authentication.symmetricKey.primaryKey + '"');
         process.exit(0);
       });
     });
   });
   
   

This app creates a device identity with ID myFirstDevice and a module identity with ID myFirstModule under device myFirstDevice. (If that module ID already exists in the identity registry, the code simply retrieves the existing module information.) The app then displays the primary key for that identity. You use this key in the simulated module app to connect to your IoT hub.

Run this using node add.js. It will give you a connection string for your device identity and another one for your module identity.

Update the module twin using Node.js device SDK

In this section, you create a Node.js app on your simulated device that updates the module twin reported properties.

1. Get your module connection string -- Sign in to the Azure portal. Navigate to your IoT Hub and click IoT Devices. Find myFirstDevice, open it and you see myFirstModule was successfully created. Copy the module connection string. It is needed in the next step.

   

2. Similar to what you did in the step above, create a directory for your device code and use NPM to initialize it and install the device SDK (npm install -S azure-iot-device-amqp@modules-preview).

   Note

   The npm install command may feel slow. Be patient -- it's pulling down lots of code from the package repository.

   Note

   If you see an error that says npm ERR! registry error parsing json, this is safe to ignore. If you see an error that says npm ERR! registry error parsing json, this is safe to ignore.

3. Create a file called twin.js. Copy and paste your module identity string.

   var Client = require('azure-iot-device').Client;
   var Protocol = require('azure-iot-device-amqp').Amqp;
   // Copy/paste your module connection string here.
   var connectionString = '<insert module connection string here>';
   // Create a client using the Amqp protocol.
   var client = Client.fromConnectionString(connectionString, Protocol);
   client.on('error', function (err) {
     console.error(err.message);
   });
   // connect to the hub
   client.open(function(err) {
     if (err) {
       console.error('error connecting to hub: ' + err);
       process.exit(1);
     }
     console.log('client opened');
   // Create device Twin
     client.getTwin(function(err, twin) {
       if (err) {
         console.error('error getting twin: ' + err);
         process.exit(1);
       }
       // Output the current properties
       console.log('twin contents:');
       console.log(twin.properties);
       // Add a handler for desired property changes
       twin.on('properties.desired', function(delta) {
           console.log('new desired properties received:');
           console.log(JSON.stringify(delta));
       });
       // create a patch to send to the hub
       var patch = {
         updateTime: new Date().toString(),
         firmwareVersion:'1.2.1',
         weather:{
           temperature: 72,
           humidity: 17
         }
       };
       // send the patch
       twin.properties.reported.update(patch, function(err) {
         if (err) throw err;
         console.log('twin state reported');
       });
     });
   });
   

4. Now, run this using the command node twin.js.

   F:\temp\module_twin>node twin.js
   

   You will then see:

   client opened
   twin contents:
   { reported: { update: [Function: update], '$version': 1 },
     desired: { '$version': 1 } }
   new desired properties received:
   {"$version":1}
   twin state reported
   

Next steps

To continue getting started with IoT Hub and to explore other IoT scenarios, see:

• Getting started with device management

• Getting started with IoT Edge