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    2.3.1 • Public • Published


    This library provides support for managing configuration settings in Azure IoT microservices.

    Developer Setup

    1. Install Node

    Node can be found here.

    2. npm install

    This downloads and installs all dependencies required to support this library.

    3. npm run build

    This builds the project, putting the output into the base (./dist) folder.


    This library provides the main Configuration module, which exports the config singleton to create a dictionary-like interface of configuration values. Once initialized, config provides the getSecret, getString and generic get<T> methods, described further below.


    Configuration keys are mapped to values from one of four optional providers, in order of preference:

    • file: JSON file at ./user-config.json
    • env: environment variables
    • mongo: Mongo DB at the address of the MONGO_URI configuration variable
    • default: default values passed as an optional argument to config.initialize

    The first provider to return a value other than null is considered authoritative. For example, if both the file and default providers contained a value for the same key, the file provider would be authoritative.

    The library also provides support for fetching secret configuration values from KeyVault, using a separate keyVault provider. This credentials to initialize the connection to KeyVault is fetched from the other providers listed below, but once set up, secrets are fetched using a separate getSecret API, not the usual getString and get<T> methods. The examples listed below demonstrate how to read and write secrets from KeyVault.

    Setting variables

    Configuration variables only need to be set for one configuration provider. Variables can be set for each of the providers in the following ways:

    • file provider: include the key-value pair in ./user-config.json

    • env provider: set an environment variable; for non-string values, set the stringified version of the object

    • mongo provider: either set key-value pairs directly, or use MongoConfiguration.set

    • default provider: include the key-value pair in the optional defaultValues parameter for config.initialize

    • keyVault provider: set the secret using the Azure XPlat CLI, provide the values to authenticate with keyvault using the other providers listed below, and then fetch secrets using the getSecret method.

    See the Example section for more.

    Getting variables

    The config singleton (and each provider) implements the IConfiguration interface, which provides the get<T>, getString, and getSecret methods:

    • get<T>(key): use when you expect the returned value to be anything other than a string; e.g. an object, array, etc.
    • getString(key): use when you expect the returned value to be a string
    • getSecret(key): use then you have to fetch secrets from KeyVault.

    Both methods return null if no value is set for the passed key.

    The key parameter can be either a string or an array of strings. If key is a string, get and getString return the associated value. If key is an array, however, get and getString will walk down through a nested object to return the associated value. For example:

    // Let's say config.get('KEY') -> { 'fruits': ['apples', 'bananas'] }
    let outerValue = config.get('KEY');
    let innerValue = config.get(['KEY', 'fruits']);
    let missingValue = config.get(['KEY', 'vegetables']);
    // This leaves us with:
    // outerValue = { 'fruits': ['apples', 'bananas'] }
    // innerValue = ['apples', 'bananas']
    // missingValue = null
    // Fetching secrets:
    // let's say config.get("AAD_SECRET") -> { "id": "https://foo.vault.azure.net/secrets/aad-secret"}
    const aadSecret = await config.getSecret('AAD_SECRET');
    // This will fetch the keyvault secret's URL from other providers,
    // fetch the secret value from keyvault, and return an object with
    // the following format:
    aadSecret = {
        id: "https://foo.vault.azure.net/secrets/aad-secret",
        value: "<secret value>"

    Initializing config

    The config singleton takes a single, optional ConfigOptions argument to its asynchronous initialize call. The ConfigOptions object contains a number of options, including:

    • defaultValues: an object of key-value pairs which serve as default values---i.e. defaultValues is consulted if all other providers return null; defaults to an empty object
    • requiredKeys: an array of variable names which must be assigned a value before returning from the initialization; defaults to an empty array
    • configFilename: the location of the JSON file provider relative to the calling process's working directory; defaults to ./user-config.json
    • logger: function to call in place of console.log

    Note: requiredKeys and defaultValues should not share any keys. Sharing keys between these arguments results in unspecified behavior.


    Provisioning a provider

    This example creates a file provider sourced from ./user-config.json and a mongo provider sourced from the Mongo DB at the location of MONGO_URI.

    Let's say we have the following as our ./user-config.json file:

        "SERVICES": {
                "service_1": {
                    "name": "foo",
                    "href": "bar.com",
        "MONGO_URI": "mongodb://localhost:27017",
        "MONGO_CONFIG_DB": "config-db",
        "MONGO_CONFIG_COLLECTION": "config-collection",
        "SHARED_KEY": null

    This means, e.g., config.getString(['services', 'service_1', 'name']) -> 'foo'.

    Now, to provision a mongo provider with service_2, we'll choose

    • database: config-db (set by the MONGO_CONFIG_DB in the above user-config.json)
    • collection: config-collection (set by the MONGO_CONFIG_COLLECTION in the above user-config.json)
    • document: N/A (the collection must contain only a single document)

    Then, in the config-db database, set the config-collection collection's single document to be:

        "SERVICES": {
                "service_2": {
                    "name": "soap",
                    "href": "soup.com",
        "SHARED_KEY": "sap"

    This results in the following:

    import {config} from '@azure-iot/configuration';
    config.initialize().then( () => {
        let mongoUri = config.getString('MONGO_URI');
        let servicesObject_1 = config.get('SERVICES');
        let service_2 = config.get(['SERVICES', 'service_2']);
        let serviceName_2 = config.getString(['SERVICES', 'service_2', 'name']);
        let sharedKey = config.getString('SHARED_KEY');
        // Now, we have:
        // mongoUri = 'mongodb://localhost:27017'
        // servicesObject_1 = { 'service_1': { 'name': 'foo', ... } }
        // service_2 = { 'name': 'soap', ... }
        // serviceName_2 = 'soap'
        // sharedKey = 'sap'

    Using the default provider

    This example uses the env provider to draw from environment variables, but falls back on the default provider which draws from the defaultValues objects passed to config.initialize.

    Remember that the strict order of provider preference is file, env, mongo, and then default.

    import {config} from '@azure-iot/configuration';
    async function example(): Promise<void> {
        // Set an environment variable
        process.env['SOUP'] = 'soap';
        // Create an object of default values
        let defaultValues = {
            'FRUITS': ['cherries', 'dates'],
            'REQUIRED_KEY': 'bar'
        // Asynchronously initialize the config service
        // with default values; won't return from initializing
        // until REQUIRED_KEY has a value
        await config.initialize({
            requiredKeys: ['REQUIRED_KEY'],
            defaultValues: defaultValues
        // Get values from the config instance
        let soup = config.getString('soup');
        let fruits = config.get('FRUITS');
        // Now, we have:
        // soup = 'soap'
        // fruits = ['cherries', 'dates']

    Using the KeyVault provider

    1. Initialize the connection to KeyVault with the authentication parameters. Ensure you have the following configuration available in the file/env/mongo/default providers:

      KEYVAULT: {
          clientId: '<Client ID of the AAD application that has access to the KeyVault>',
          certFile: '<Path to the service principal's certificate>',
          certThumbprint: '<Thumbprint of the service principal's certificate>'

      The config.initialize method initializes the keyvault provider only if the KEYVAULT configuration value is present in one of the other providers.

    2. Once initialized, call the getSecret method to fetch the secret value from KeyVault:

      // Fetching secrets:
      // let's say config.get("AAD_SECRET") -> { "id": "https://foo.vault.azure.net/secrets/aad-secret"}
      const aadSecret = await config.getSecret('AAD_SECRET');
      // This will fetch the keyvault secret's URL from other providers,
      // fetch the secret value from keyvault, and return an object with
      // the following format:
      aadSecret = {
          id: "https://foo.vault.azure.net/secrets/aad-secret",
          value: "<secret value>"

    Add secrets to KeyVault:

    1. Install the Azure XPlat CLI
    2. azure login
    3. azure account set <subscription name>
    4. Create the KeyVault, if you don't already have one:
      azure keyvault create <vault-name> <resource-group> <location>
    5. Add secrets to KeyVault:
      azure keyvault secret set <vault-name> <secret-name> <secret-value>

    Create a service principal with access to KeyVault:

    1. Create RSA cert From https://unix.stackexchange.com/questions/131334/obtain-cer-file-from-pem-file

      openssl genrsa -out keyvault.pem 4096
    2. Create celf-signed x509 cert:

      openssl req -new -x509 -key keyvault.pem -out keyvault.cacert.pem -days 365
    3. Convert .pem file to .cer:

      openssl x509 -inform PEM -in keyvault.cacert.pem -outform DER -out keyvault.cer
    4. In powershell: From https://azure.microsoft.com/en-us/documentation/samples/active-directory-dotnet-daemon-certificate-credential/

      $cer = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2
      $bin = $cer.GetRawCertData()
      $base64Value = [System.Convert]::ToBase64String($bin)
      $bin = $cer.GetCertHash()
      $base64Thumbprint = [System.Convert]::ToBase64String($bin)
      $keyid = [System.Guid]::NewGuid().ToString()
    5. Download manifest of AAD app

    6. Open the manifest if your favorite text editor, and replace the keyCredentials property with your new certificate information from above, using the following schema:

      "keyCredentials": [
              "customKeyIdentifier": "$base64Thumbprint_from_above",
              "keyId": "$keyid_from_above",
              "type": "AsymmetricX509Cert",
              "usage": "Verify",
              "value":  "$base64Value_from_above"
    7. Save the edits to the application manifest, and upload it back into Azure AD by clicking Manage Manifest --> Upload Manifest. Note that the keyCredentials property is multi-valued, so you may upload multiple certificates for richer key managemnent.

    8. Get the Object ID of the AAD app's service principal:

      > azure ad sp show --spn <aad client id>
      info:    Executing command ad sp show
      + Getting Active Directory service principals
      data:    Object Id:               <object id of the service principal>
    9. Give the AAD Keyvault app access to the keyvault:

      azure keyvault set-policy <vault-name> --object-id <object-id-of-spn> --perms-to-secrets "[\"get\"]"


    Recommended key casing

    The below choices in key casing are best practices for the current usages of this library.

    • Always prefer underscores to dashes (e.g. foo_bar rather than foo-bar)
    • Top-level configuration keys should be in SCREAMING_SNAKE_CASE (all caps, underscores)
    • All other configuration keys should be in snake_case (all lowercase, underscores)

    Recommended configuration schema

    The below sample JSON file demonstrates best practices for organizing configuration variables.

        "PORT": "9001",
        "IOTHUB_CONNECTION_STRING": "HostName=...",
        "CONSOLE_REPORTING": "both",
        "LOG_LEVEL": "warn",
        "SERVICES": {
            "service_1": {
                "href": "http://foo.com"
            "service_2": {
                "href": "http://bar.com"

    Setting MONGO_URI

    In order to utilize a mongo provider, the MONGO_URI configuration variable must be set by one of the other three providers. If no value is found for MONGO_URI, config.initialize will not attempt to connect to a Mongo DB. A good fallback is to set a default value for MONGO_URI in the default provider (passed as the defaultValues object to config.initialize).

    MongoDB notes

    Setting a source. Choosing the database, collection, and document to source for configuration variables is shown below.

    • Database: utilized DB is pulled from the MONGO_CONFIG_DB configuration variable; defaults to config
    • Collection: the utilized collection is pulled from the MONGO_CONFIG_COLLECTION configuration variable; defaults to config
    • Document: currently, the chosen collection must contain only a single document

    Waiting for variables. Let's say another microservice is inserting variables into the Mongo DB in parallel to the calling of config.initialize. By specifying the requiredKeys argument to config.initialize, the method will wait until all of the keys in requiredKeys have been found by any provider. For example, to wait for the SERVICES key to appear in the mongo provider (and assuming there is no SERVICES key in either the file or env providers), you would initialize config with config.initialize({requiredKeys: ['SERVICES']}).

    Shallow reads. Because get and getString are synchronous methods, reads to the mongo provider are necessarily shallow reads. To ensure that the provider has values for certain keys before returning from initialization, utilize the requiredKeys parameter to config.initialize.

    get vs getString

    • get<T> returns file, mongo, and default values as-is, and attempts to JSON.parse top-level values from env; casts the return value as T
    • getString returns all values as-is, and attempts to throw an error if the value is not a string

    Using providers directly

    Each provider can also be used independently of Configuration. Specifically, the MongoConfiguration class can be used to set values through to a Mongo DB directly, as shown below:

    import {MongoConfiguration} from '@azure-iot/configuration';
    async function usingProviders() {
        let mongoConfig = new MongoConfiguration();
        await mongoConfig.initialize({
            mongoUri: 'mongodb://localhost:27017'
        await mongoConfig.set('fruitKey', {'fruits': ['apple', 'banana']});
        // Now, the config collection of the config DB on the
        // localhost connection should contain the fruitKey
        // variable




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