Feature Flags/Toggles

Mind Map Summary

• Topic: Feature Flags/Toggles
• Definition: A technique that allows you to turn features of your application on or off without deploying new code.
• Use Cases:
  • Decouple Deployment from Release: Deploy new features to production but keep them hidden from users until they are ready to be released.
  • Canary Releases: Gradually roll out new features to a small subset of users before releasing them to everyone.
  • A/B Testing: Test different versions of a feature with different groups of users to see which one performs better.
  • Kill Switch: Quickly disable a feature that is causing problems in production.
• Risks:
  • Increased Complexity: Feature flags can add complexity to the codebase.
  • Technical Debt: Old feature flags can become technical debt if they are not removed.
  • Testing Challenges: It can be difficult to test all the different combinations of feature flags.

Practice Exercise

Implement a simple feature flag system (or use a library like Microsoft.FeatureManagement). Create an API endpoint that behaves differently depending on whether a feature flag is enabled or disabled. Show how you can change the application’s behavior without redeploying the code.

Answer

1. Install the NuGet Package:

dotnet add package Microsoft.FeatureManagement.AspNetCore

2. Configure Feature Flags in appsettings.json:

{
  "FeatureManagement": {
    "NewAwesomeFeature": true
  }
}

3. Register Feature Management in Program.cs:

builder.Services.AddFeatureManagement();

4. Use Feature Flags in an API Controller:

using Microsoft.AspNetCore.Mvc;
using Microsoft.FeatureManagement;

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

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

    [HttpGet]
    public async Task<IActionResult> Get()
    {
        if (await _featureManager.IsEnabledAsync("NewAwesomeFeature"))
        {
            return Ok("The new awesome feature is enabled!");
        }
        else
        {
            return Ok("The old feature is still here.");
        }
    }
}

5. Change the Feature Flag:

To change the behavior of the application, you can simply change the value of the NewAwesomeFeature flag in appsettings.json and restart the application. You do not need to redeploy the code.