Real-Time Feature Flagging

In this lesson, you will learn how to use runtime configuration changes to toggle SignalR features on and off without restarting your server or reconnecting clients.

The Concept of Real-Time Feature Flagging

In high-scale systems, deploying code to disable a broken or resource-intensive feature is too slow. By integrating an IOptionsMonitor or a distributed configuration provider with your SignalR Hub, you can gate specific methods or broadcasts. The trick is to check the configuration state at the exact moment a hub method is invoked, rather than caching the state during the Hub's lifecycle.

Implementing the Gate

Because a Hub instance is transient (created per invocation), you can inject IOptionsMonitor<T> to ensure that every call evaluates the current configuration in real-time.

public class FeatureHub : Hub
{
    private readonly IOptionsMonitor<FeatureSettings> _settings;

    public FeatureHub(IOptionsMonitor<FeatureSettings> settings)
    {
        _settings = settings;
    }

    public async Task SendLiveUpdate(string message)
    {
        // Check if the feature is enabled at runtime
        if (!_settings.CurrentValue.IsLiveStreamingEnabled)
        {
            throw new HubException("This feature is currently disabled.");
        }

        await Clients.All.SendAsync("ReceiveUpdate", message);
    }
}

Why This Matters for Real-Time

When using SignalR, you often deal with "hot paths"—code that executes thousands of times per second. By using IOptionsMonitor, your application reacts immediately to changes in your configuration source (like Azure App Configuration or a database flag) without needing to cycle the HubContext.

If the flag is disabled, you can stop the broadcast flow instantly. This prevents the server from processing heavy payloads for features that need to be "dark-launched" or emergency-killed. This approach works seamlessly with your existing infrastructure, ensuring that your real-time layer remains as agile as your core business logic.

Key Takeaway: Use IOptionsMonitor within your Hub to evaluate feature flags at the point of invocation, allowing you to toggle real-time functionality instantly across your entire cluster.