As .NET developers, we often face the challenge of deploying new features to production safely. The anxiety of a breaking change hitting live users is real. What if you could deploy code containing a new feature but keep it hidden until you’re absolutely sure it’s ready? This is where feature flags, powered by the Microsoft.FeatureManagement library, become invaluable. They allow you to dynamically enable or disable functionality in your ASP.NET Core application at runtime, decoupled from deployments.
Integrating feature flags is straightforward. First, add the Microsoft.FeatureManagement.AspNetCore NuGet package to your project. Then, configure your feature flags in appsettings.json. You can define simple boolean flags or more complex scenarios using custom filters. For instance, to enable a new dashboard feature for a specific group of users, you could define it like this:
{
"FeatureManagement": {
"NewDashboard": true,
"BetaFeatureForAdmins": false
}
}
In your ASP.NET Core application, you can then inject IFeatureManager into your controllers or services. This allows you to check the state of a feature flag and conditionally execute code. For example, in a controller action, you can use _featureManager.IsEnabledAsync("NewDashboard") to determine whether to show the new dashboard or fall back to the old implementation. This provides a powerful mechanism for A/B testing, phased rollouts, and quick rollbacks without needing a new deployment.
For more advanced control and integration with AI-assisted coding, Claude Code can help you generate the boilerplate code for feature flag checks. You can prompt Claude Code to create C# snippets that inject IFeatureManager and perform conditional logic based on flag states. This streamlines the process of implementing feature flags across your codebase, saving valuable development time.
Try it: Add Microsoft.FeatureManagement.AspNetCore to your ASP.NET Core project, define a MyNewFeature flag in appsettings.json, and then use _featureManager.IsEnabledAsync("MyNewFeature") in a controller to conditionally return different results.