Tutorial: Use dynamic configuration in a .NET Core app

• 07/01/2019
• 4 minutes to read
• • 
  • 
  • 
  • 

The App Configuration .NET Core client library supports updating a set of configuration settings on demand without causing an application to restart. This can be implemented by first getting an instance of IConfigurationRefresher from the options for the configuration provider and then calling Refresh on that instance anywhere in your code.

In order to keep the settings updated and avoid too many calls to the configuration store, a cache is used for each setting. Until the cached value of a setting has expired, the refresh operation does not update the value, even when the value has changed in the configuration store. The default expiration time for each request is 30 seconds, but it can be overridden if required.

This tutorial shows how you can implement dynamic configuration updates in your code. It builds on the app introduced in the quickstarts. Before you continue, finish Create a .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

Open Program.cs and update the file to add a reference to the System.Threading.Tasks namespace, to specify refresh configuration in the AddAzureAppConfiguration method, and to trigger manual refresh using the Refresh method.

using System;
using System.Threading.Tasks;

namespace TestConsole
{
class Program
{
    private static IConfiguration _configuration = null;
    private static IConfigurationRefresher _refresher = null;

    static void Main(string[] args)
    {
        var builder = new ConfigurationBuilder();
        builder.AddAzureAppConfiguration(options =>
        {
            options.Connect(Environment.GetEnvironmentVariable("ConnectionString"))
                    .ConfigureRefresh(refresh =>
                    {
                        refresh.Register("TestApp:Settings:Message")
                               .SetCacheExpiration(TimeSpan.FromSeconds(10));
                    });
                    
                    _refresher = options.GetRefresher();
        });

        _configuration = builder.Build();
        PrintMessage().Wait();
    }

    private static async Task PrintMessage()
    {
        Console.WriteLine(_configuration["TestApp:Settings:Message"] ?? "Hello world!");

        // Wait for the user to press Enter
        Console.ReadLine();

        await _refresher.Refresh();
        Console.WriteLine(_configuration["TestApp:Settings:Message"] ?? "Hello world!");
    }
}
}

The ConfigureRefresh method is used to specify the settings used to update the configuration data with the App Configuration store when a refresh operation is triggered. An instance of IConfigurationRefresher can be retrieved by calling GetRefresher method on the options provided to AddAzureAppConfiguration method, and the Refresh method on this instance could be used to trigger a refresh operation anywhere in your code.

Build and run the app locally

1. Set an environment variable named ConnectionString, and set it to the access key to your App Configuration store. If you use the Windows command prompt, run the following command and restart the command prompt to allow the change to take effect:

    setx ConnectionString "connection-string-of-your-app-configuration-store"
   

   If you use Windows PowerShell, run the following command:

    $Env:ConnectionString = "connection-string-of-your-app-configuration-store"
   

   If you use macOS or Linux, run the following command:

    export ConnectionString='connection-string-of-your-app-configuration-store'
   

2. Run the following command to build the console app:

    dotnet build
   

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

    dotnet run
   

   

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
   TestApp:Settings:Message	Data from Azure App Configuration - Updated

6. Press the Enter key to trigger a refresh and print the updated value in the Command Prompt or PowerShell window.

   

   Note

   Since the cache expiration time was set to 10 seconds using the SetCacheExpiration method while specifying the configuration for the refresh operation, the value for the configuration setting will only be updated if at least 10 seconds have elapsed since the last refresh for that setting.

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.

1. Sign in to the Azure portal, and select Resource groups.
2. In the Filter by name box, enter the name of your resource group. The instructions for this quickstart used a resource group named AppConfigTestResources.
3. In the result list, select the resource group, and either right-click the row or use the ellipsis (...) button to open the context menu.
4. Select Delete resource group.
5. 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 its resources are deleted.

Next steps

In this tutorial, you enabled your .NET Core app to dynamically refresh configuration settings from App Configuration. To learn how to use an Azure managed identity to streamline the access to App Configuration, continue to the next tutorial.