You've probably heard developers talking about "feature flags" or "feature toggles," but what exactly are they? And why is every successful tech company from Netflix to Facebook using them?
If you've ever been nervous about deploying new code to production, or wished you could test features with real users before a full rollout, this guide is for you.
What Are Feature Flags?
Feature flags are simple conditional statements in your code that let you turn features on or off without deploying new code. Think of them as light switches for your application features.
Instead of this:
function Header() {
return (
<header>
<NewDesign /> // Always shows new design
</header>
);
}
You write this:
function Header() {
const showNewDesign = useFeatureFlag('new-header-design');
return (
<header>
{showNewDesign ? <NewDesign /> : <OldDesign />}
</header>
);
}
Now you can control which users see the new design without touching your code.
Why Do Feature Flags Matter?
1. Deploy Without Fear
Remember that sinking feeling when your deployment breaks production? Feature flags let you deploy code that's "off" by default. If something goes wrong, you flip a switch instead of scrambling to fix code.
2. Test with Real Users
You can show new features to 5% of users, gather feedback, and gradually increase the rollout. No more guessing if users will like your changes.
3. Faster Development
Teams can work on features independently and merge code even if features aren't ready. Just keep the flag off until you're ready to launch.
4. Instant Rollbacks
Found a bug in production? Turn off the feature flag in seconds, not hours.
Common Feature Flag Use Cases
A/B Testing
Show 50% of users the blue button, 50% the red button. See which converts better.
const buttonColor = useFeatureFlag('blue-cta-button') ? 'blue' : 'red';
Gradual Feature Rollouts
Roll out new features to a small percentage of users first, then gradually increase.
// Show new checkout flow to 10% of users initially
const useNewCheckout = useFeatureFlag('new-checkout-flow');
Kill Switches
Instantly disable resource-heavy features if your servers are struggling.
const enableExpensiveFeature = useFeatureFlag('heavy-analytics');
if (!enableExpensiveFeature) return <LightweightVersion />;
Beta Features
Give premium users early access to new features.
const showBetaFeatures = user.isPremium && useFeatureFlag('beta-access');
Types of Feature Flags
Release Flags
Short-lived flags for new feature rollouts. Delete these after full deployment.
const showNewDashboard = useFeatureFlag('dashboard-v2'); // Delete after 100% rollout
Experiment Flags
For A/B testing and experimentation. Keep these during the experiment period.
const variant = useFeatureFlag('signup-experiment'); // 'control' or 'variant'
Operational Flags
Long-lived flags for system control and circuit breakers.
const enableEmailNotifications = useFeatureFlag('email-system-enabled');
Permission Flags
Control access to features based on user roles or plans.
const canAccessAdvancedFeatures = user.plan === 'pro' && useFeatureFlag('pro-features');
Feature Flag Best Practices
1. Use Descriptive Names
// ❌ Bad
const flag1 = useFeatureFlag('f1');
// ✅ Good
const showNewPricingPage = useFeatureFlag('new-pricing-page-v2');
2. Clean Up Old Flags
Feature flags create technical debt. Remove flags once features are fully rolled out.
// After 100% rollout, replace this:
const showNewFeature = useFeatureFlag('new-feature');
return showNewFeature ? <NewFeature /> : <OldFeature />;
// With this:
return <NewFeature />;
3. Default to Safe States
If your feature flag service is down, default to the stable version.
const showExperimentalFeature = useFeatureFlag('experimental-ui') ?? false;
4. Monitor Flag Usage
Track which features are being used and how they're performing.
5. Limit Flag Complexity
Avoid nested flags and complex logic. Keep it simple.
// ❌ Avoid this complexity
if (useFeatureFlag('A') && useFeatureFlag('B') && !useFeatureFlag('C')) {
// Complex logic
}
// ✅ Better approach
const showComplexFeature = useFeatureFlag('complex-feature-enabled');
How to Implement Feature Flags
DIY Approach
You can start with a simple implementation:
// Simple feature flag store
const featureFlags = {
'new-header': true,
'beta-dashboard': false,
'experiment-checkout': true
};
function useFeatureFlag(flagName) {
return featureFlags[flagName] ?? false;
}
For more advanced DIY implementations, you might want to add a confidence score system that automatically adjusts rollout percentages based on error rates and user feedback. Martin Fowler has an excellent guide on feature flag confidence patterns if you want to explore this approach.
Pros: Free, simple to understand, full control Cons: No dynamic updates, no user targeting, no analytics, requires manual monitoring
Using a Feature Flag Service
For production applications, you'll want a dedicated service that provides:
- Dynamic updates - Change flags without code deployment
- User targeting - Show features to specific users or groups
- Gradual rollouts - Start with 5%, increase to 100%
- Analytics - Track flag performance and usage
- Team collaboration - Non-technical team members can control flags
Popular options include LaunchDarkly, Split.io, and newer solutions like GradualRollout that combine feature flags with canary deployment capabilities.
Think of this like Apple's phased app releases on the App Store - they roll out iOS updates to a small percentage of users first, monitor for issues, then gradually increase the rollout. Feature flag services let you do the same thing with individual features in your web application.
Feature Flags vs Canary Deployments: What's the Difference?
While feature flags and canary deployments are often mentioned together, they're actually different techniques that solve different problems:
Feature Flags
- Same codebase - New and old features exist in the same deployed code
- Instant switching - Toggle features on/off immediately via configuration
- Code-level control - Different users see different features from the same deployment
Canary Deployments
- Different codebases - You deploy new code to a subset of servers
- Infrastructure-level - Route traffic between old and new deployments
- Gradual replacement - Slowly replace old code with new code across your infrastructure
Think of it this way: Feature flags are like having multiple light switches in the same room, while canary deployments are like having multiple rooms with different lighting setups.
Feature Flags + Canary Deployments: The Power Combo
The magic happens when you combine both approaches:
- Deploy new code via canary deployment (5% of servers get new code)
- Add feature flags in the new code for extra safety
- Enable flags gradually within the canary group
- Monitor both deployment health AND feature performance
- Scale up safely with double protection
This is like Apple's approach to iOS updates - they use phased releases (canary-style infrastructure rollout) AND feature flags within iOS to control when new features become visible to users. You get infrastructure safety AND feature-level control.
This approach lets you:
- Catch issues before they affect all users
- Get real user feedback on small groups
- Make data-driven rollout decisions
- Sleep better knowing you can rollback instantly
Common Pitfalls to Avoid
1. Flag Sprawl
Don't let old flags accumulate. Create a cleanup schedule.
2. Testing Complexity
Test both flag states in your CI/CD pipeline.
3. Performance Impact
Too many flag evaluations can slow down your app. Cache flag values when possible.
4. Configuration Drift
Keep flag configurations in version control when possible.
5. Overengineering
Start simple. You can always add complexity later.
When NOT to Use Feature Flags
Feature flags aren't always the answer:
- Database schema changes - These often require careful migration strategies
- Security fixes - Deploy these immediately, don't hide behind flags
- Simple bug fixes - Just fix and deploy
- Breaking API changes - Use versioning instead
Getting Started Today
Ready to add feature flags to your application? Here's your action plan:
Week 1: Start Simple
- Identify one new feature you're working on
- Wrap it in a simple feature flag
- Test both enabled and disabled states
Week 2: Add Targeting
- Implement basic user targeting (show to specific users)
- Try a small percentage rollout (5-10% of users)
Week 3: Monitor and Measure
- Add basic analytics to track flag usage
- Monitor error rates and performance
- Practice rolling back a feature
Week 4: Scale Up
- Add feature flags to more features
- Involve non-technical team members in flag management
- Consider a dedicated feature flag service
The Bottom Line
Feature flags might seem like extra complexity at first, but they're actually a simplicity tool. They simplify deployments, reduce risk, and give you confidence to ship faster.
Every developer has that story about a deployment that went wrong. Feature flags help ensure your next deployment story is a good one.
The question isn't whether you should use feature flags—it's which approach will work best for your team. Start simple, learn as you go, and gradually build up your feature flag strategy.
Your future self (and your users) will thank you.
Next Steps
Want to see feature flags in action? Try our interactive demo that shows feature flags combined with canary deployments, or check out our guide on implementing your first feature flag in React.
Questions about feature flags? Drop us a line at [contact@gradualrollout.com] - we love talking about safe deployment strategies!
💡 Full Transparency: GradualRollout is an indie project currently in beta. As a solo founder building this platform, I'd love your feedback on what features would be most valuable for your deployment workflow. Your input will directly shape the future of the product! Feel free to reach out on Twitter/X or through our contact form.
Feature flags are just the beginning. Learn how combining them with canary deployments can make your deployments even safer with GradualRollout.
