Tutorial: Use dynamic configuration in an ASP.NET Core app

• 02/24/2019
• 4 minutes to read
• Contributors
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ASP.NET Core has a pluggable configuration system that can read configuration data from a variety of sources. It can handle changes on the fly without causing an application to restart. ASP.NET Core supports the binding of configuration settings to strongly typed .NET classes. It injects them into your code by using the various IOptions<T> patterns. One of these patterns, specifically IOptionsSnapshot<T>, automatically reloads the application's configuration when the underlying data changes.

You can inject IOptionsSnapshot<T> into controllers in your application to access the most recent configuration stored in Azure App Configuration. You also can set up the App Configuration ASP.NET Core client library to continuously monitor and retrieve any change in an app configuration store. You define the periodic interval for the polling.

This tutorial shows how you can implement dynamic configuration updates in your code. It builds on the web app introduced in the quickstarts. Before you continue, finish Create an ASP.NET Core app with App Configuration first.

You can use any code editor to do the steps in this tutorial. Visual Studio Code is an excellent option that's available on the Windows, macOS, and Linux platforms.

In this tutorial, you learn how to:

Prerequisites

To do this tutorial, install the .NET Core SDK.

If you don't have an Azure subscription, create a free account before you begin.

Reload data from App Configuration

1. Open Program.cs, and update the CreateWebHostBuilder method by adding the config.AddAzureAppConfiguration() method.

   public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
       WebHost.CreateDefaultBuilder(args)
           .ConfigureAppConfiguration((hostingContext, config) =>
           {
               var settings = config.Build();
               config.AddAzureAppConfiguration(options =>
                   options.Connect(settings["ConnectionStrings:AppConfig"])
                          .Watch("TestApp:Settings:BackgroundColor")
                          .Watch("TestApp:Settings:FontColor")
                          .Watch("TestApp:Settings:Message"));
           })
           .UseStartup<Startup>();
   

   The second parameter in the .Watch method is the polling interval at which the ASP.NET client library queries an app configuration store. The client library checks the specific configuration setting to see if any change occurred.

   Note

   The default polling interval for the Watch extension method is 30 seconds if not specified.

2. Add a Settings.cs file that defines and implements a new Settings class.

   namespace TestAppConfig
   {
       public class Settings
       {
           public string BackgroundColor { get; set; }
           public long FontSize { get; set; }
           public string FontColor { get; set; }
           public string Message { get; set; }
       }
   }
   

3. Open Startup.cs, and update the ConfigureServices method to bind configuration data to the Settings class.

   public void ConfigureServices(IServiceCollection services)
   {
       services.Configure<Settings>(Configuration.GetSection("TestApp:Settings"));
   
       services.Configure<CookiePolicyOptions>(options =>
       {
           options.CheckConsentNeeded = context => true;
           options.MinimumSameSitePolicy = SameSiteMode.None;
       });
   
       services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
   }
   

Use the latest configuration data

1. Open HomeController.cs in the Controllers directory, and add a reference to the Microsoft.Extensions.Options package.

   using Microsoft.Extensions.Options;
   

2. Update the HomeController class to receive Settings through dependency injection, and make use of its values.

   public class HomeController : Controller
   {
       private readonly Settings _settings;
       public HomeController(IOptionsSnapshot<Settings> settings)
       {
           _settings = settings.Value;
       }
   
       public IActionResult Index()
       {
           ViewData["BackgroundColor"] = _settings.BackgroundColor;
           ViewData["FontSize"] = _settings.FontSize;
           ViewData["FontColor"] = _settings.FontColor;
           ViewData["Message"] = _settings.Message;
   
           return View();
       }
   }
   

3. Open Index.cshtml in the Views > Home directory, and replace its content with the following script:

   <!DOCTYPE html>
   <html lang="en">
   <style>
       body {
           background-color: @ViewData["BackgroundColor"]
       }
       h1 {
           color: @ViewData["FontColor"];
           font-size: @ViewData["FontSize"];
       }
   </style>
   <head>
       <title>Index View</title>
   </head>
   <body>
       <h1>@ViewData["Message"]</h1>
   </body>
   </html>
   

Build and run the app locally

1. To build the app by using the .NET Core CLI, run the following command in the command shell:

    dotnet build
   

2. After the build successfully completes, run the following command to run the web app locally:

    dotnet run
   

3. Open a browser window, and go to http://localhost:5000, which is the default URL for the web app hosted locally.

   

4. Sign in to the Azure portal. Select All resources, and select the app configuration store instance that you created in the quickstart.

5. Select Configuration Explorer, and update the values of the following keys:

   Key	Value
   TestAppSettings:BackgroundColor	green
   TestAppSettings:FontColor	lightGray
   TestAppSettings:Message	Data from Azure App Configuration - now with live updates!

6. Refresh the browser page to see the new configuration settings.

   

Clean up resources

If you plan to continue to the next tutorial, keep the resources you created in this quickstart. You can reuse them in the next tutorial.

If you're finished with the quickstart sample application, delete the Azure resources you created in this quickstart to avoid charges.

Sign in to the Azure portal, and select Resource groups.

In the Filter by name box, enter the name of your resource group. The instructions for this quickstart used a resource group named AppConfigTestResources. On your resource group in the result list, select ... and then select Delete resource group.

You're asked to confirm the deletion of the resource group. Enter the name of your resource group to confirm, and select Delete.

After a few moments, the resource group and all of its contained resources are deleted.

Next steps

In this tutorial, you added an Azure managed service identity to streamline access to App Configuration and improve credential management for your app. To learn more about how to use App Configuration, continue to the Azure CLI samples.