Feature Flags in .NET Core with Azure

1. You need to find the feature manager and click on that menu.
   
2. Click on the Create button to create the feature flag.
   
3. Once you have clicked on the Create button, below the screen you will see. Fill in the necessary fields and click on the Apply button.
   
4. Once the feature flag is created, below is the screen you will see.
   
5. Here is the create feature flag for the filter. While creating the feature flag, you need to check the Use feature filters, then click on the Create button. After that, it will open another window for creating the filter, and you need to provide the necessary details. Once everything is configured, click on Apply to create the feature flag.
   
   
   
6. Once the feature flag with filter is created, you will see the below screen.
   
7. If you want to edit any of the feature flag values, then it's also possible here. Click on the horizontal 3 dots on the right side of the feature list page. Once you click on the 3 dots, it will open the popup menu, and if you click on edit, it will open a window for you to update or change the configuration value.
   
8. If you want to click on Advance Edit, then it will open a JSON format window to change the configuration value. Once you have changed the configuration value, click on the Apply button. If you want to discard your changes, then you need to click on the Discard button.
   
9. If you want to delete any of the feature flags, then it is also possible here. Click on the 3 dots on the right side and click on the Delete button.
   
10. If you want to enable or disable any of the feature flags, you need to click on the switch.
    

Let’s check on the .Net Core side.

You need to install the below packages in the .net core application.

1. Microsoft.Azure.AppConfiguration.AspNetCore
2. Microsoft.FeatureManagement.AspNetCore

Once you have been installed, you will need to register in the Program.cs file.

builder.Configuration.AddAzureAppConfiguration(options =>
{
    options.Connect(connectionString)

    // Configure to reload configuration if the registered sentinel key is modified
    .ConfigureRefresh(refreshOptions =>
         refreshOptions.Register("TestFeature", refreshAll: true));

    // Load all feature flags with no label
    options.UseFeatureFlags();
}).Build();

builder.Services.AddAzureAppConfiguration();

builder.Services.AddFeatureManagement()
    .AddFeatureFilter<JaiminCustomFilter>();

The below mention is added to the middleware to use the Azure app configuration on the application side.

app.UseAzureAppConfiguration();

Here is the custom filter class (JaiminCustomFilter.cs).

[FilterAlias("JaiminCustomFilter")]
public class JaiminCustomFilter : IFeatureFilter
{
    public Task<bool> EvaluateAsync(FeatureFilterEvaluationContext context)
    {
        var settings = context.Parameters.Get<ValueSettings>();
        return Task.FromResult(settings.Value == 50);
    }
}

Here is the value settings class (ValueSettings.cs).

public class ValueSettings
{
    public int Value { get; set; }
}

Here is the code for whether the feature is enabled or disabled.

var testFeature = await _featureManager.IsEnabledAsync("TestFeature");
var beta = await _featureManager.IsEnabledAsync("Beta");

Here is the full code for getting value from Azure and giving the result as in the API response.

[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
    private readonly IFeatureManager _featureManager;

    public ValuesController(IFeatureManager featureManager)
    {
        _featureManager = featureManager;
    }

    [HttpGet]
    public async Task<IActionResult> GetAsync()
    {
        var testFeature = await _featureManager.IsEnabledAsync("TestFeature");
        
        var response = new StringBuilder();
        response.AppendLine($"{nameof(testFeature)} {testFeature} ");

        if (testFeature)
        {
            response.AppendLine($"{nameof(testFeature)} {DateTime.UtcNow:dd:MM:yyyy HH:mm:ss.fff} ");
        }

        var beta = await _featureManager.IsEnabledAsync("Beta");
        response.AppendLine($"{nameof(beta)} {beta} ");

        if (beta)
        {
            response.AppendLine($"{nameof(beta)} {DateTime.UtcNow:dd:MM:yyyy HH:mm:ss.fff} ");
        }

        return Ok(response.ToString());
    }
}

Let’s try to run the application and check the response from the API.

Let's make changes in the Azure app configuration side and after executing the API verify the response of the API.

Let’s try to change the filter value in the Azure app configuration.

We learned the new technique and evolved together.

Happy coding!