Feature Flags (Feature Toggles) in Simple Terms

What Are Feature Flags?

Feature Flags (or Feature Toggles) are like switches in your code that allow you to enable or disable certain functions without having to change the code and make a new release. They act as conditional statements that determine whether a particular feature or code path should be executed, giving developers and product managers fine-grained control over application behavior.

At their core, feature flags are simple conditional statements in your code. However, when combined with a management system, they become a powerful tool for controlling software delivery, testing, and operations. Feature flags can be as simple as a configuration file or as sophisticated as a distributed system with a user interface for managing flags across multiple applications and environments.

Why They're Needed

How It Works: A Real Example

Imagine you're developing a new version of the user dashboard on your website. Instead of immediately showing it to all users, you can use feature flags to control the rollout process.

1// Feature flag configuration
2const featureFlags = {
3  newDashboard: false,  // Initially disabled
4  betaFeatures: false,
5  darkMode: true
6};
7
8// In your application code
9function renderDashboard() {
10  if (featureFlags.newDashboard) {
11    return renderNewDashboard();
12  } else {
13    return renderOldDashboard();
14  }
15}
16
17// To enable the feature flag later (e.g., from a control panel)
18function enableNewDashboard() {
19  featureFlags.newDashboard = true;
20  // Re-render the dashboard with the new version
21  updateUI();
22}

Interactive Demo

Try out this interactive demo to see how feature flags work in practice. Toggle the switches to enable or disable different features and see how the application responds in real-time.

AWS AppConfig for Managing Feature Flags

AWS AppConfig is a service from Amazon that helps manage these "switches" without having to change code or restart the application. It provides a centralized way to store, manage, and deploy feature flags and other configuration data to your applications.

How It Works

1{
2  "features": {
3    "new_dashboard": true,
4    "beta_mode": false
5  }
6}

1# Check if the new dashboard version is enabled
2if feature_flags["features"]["new_dashboard"]:
3    # Show the new version
4    show_new_dashboard()
5else:
6    # Show the old version
7    show_old_dashboard()

Advantages of AWS AppConfig

Alternatives to AWS AppConfig

If you don't use AWS or need other capabilities, there are several alternative solutions for managing feature flags:

Modern Approach: Flags as Code

A newer approach to feature flags is the "Flags as Code" pattern, which makes flags more maintainable and type-safe. Instead of using string identifiers for flags, each flag becomes a function in your codebase [^1][^2].

1import { flag } from 'flags/next';
2
3export const newDashboardFlag = flag({
4  key: 'new-dashboard',
5  defaultValue: false,
6  decide() {
7    return false;
8  },
9});
10
11// Usage
12const showNewDashboard = await newDashboardFlag();

Advantages of Flags as Code

Conclusion

Feature Flags are a powerful tool for more flexible and secure development. They allow you to:

• Safely test new features on real users
• Respond quickly to problems
• Conduct experiments with interface and functionality
• Manage application behavior without having to release new versions

Implementing Feature Flags through AWS AppConfig is especially convenient if you already use AWS services. It allows you to centrally manage your application's functionality and quickly respond to changing requirements or issues. For those not using AWS, there are many alternative solutions available, from open-source options to commercial services with advanced capabilities.

The modern "Flags as Code" approach takes feature flags to the next level by making them more maintainable, type-safe, and integrated into your development workflow. This approach reduces errors, improves developer experience, and makes it easier to manage feature flags as your application grows.

References

• Flags as Code | Flags SDK
• AWS AppConfig Documentation
• Feature Toggles (aka Feature Flags) by Martin Fowler
• What Are Feature Flags? | LaunchDarkly Blog
• Unleash - Open Source Feature Flag & Toggle Service