Feature Flags in Production: Ship Code Without Releasing It
Deploying code and releasing features are two different things. Feature flags decouple them — ship to production, enable for specific users.
Why Feature Flags
Without flags: merge → deploy → all users see the change immediately.
With flags: merge → deploy → enable for 5% of users → monitor → roll out gradually.
Benefits:
- Kill switches for broken features without a rollback
- A/B testing at the feature level
- Beta access for specific users
- Gradual rollouts with automatic halting
Simple Implementation
// flags.ts
interface FlagConfig {
enabled: boolean;
rolloutPercentage?: number;
allowedUsers?: string[];
}
const flags: Record<string, FlagConfig> = {
'new-dashboard': { enabled: true, rolloutPercentage: 10 },
'ai-suggestions': { enabled: false },
'beta-export': { enabled: true, allowedUsers: ['user_123', 'user_456'] },
};
export function isEnabled(flagName: string, userId?: string): boolean {
const flag = flags[flagName];
if (!flag?.enabled) return false;
if (flag.allowedUsers && userId) {
return flag.allowedUsers.includes(userId);
}
if (flag.rolloutPercentage !== undefined && userId) {
// Stable hash — same user always gets same result
const hash = userId.split('').reduce((acc, c) => acc + c.charCodeAt(0), 0);
return (hash % 100) < flag.rolloutPercentage;
}
return flag.enabled;
}
Database-Backed Flags
// Prisma schema
model FeatureFlag {
id String @id @default(cuid())
name String @unique
enabled Boolean @default(false)
rolloutPercentage Int? @default(0)
updatedAt DateTime @updatedAt
}
// Toggle a flag without redeploying
await prisma.featureFlag.update({
where: { name: 'new-dashboard' },
data: { rolloutPercentage: 50 }
});
React Integration
import { useFlag } from '@/hooks/useFlag';
function Dashboard() {
const showNewUI = useFlag('new-dashboard');
return showNewUI ? <NewDashboard /> : <LegacyDashboard />;
}
// Hook implementation
function useFlag(flagName: string) {
const { user } = useAuth();
return useMemo(() => isEnabled(flagName, user?.id), [flagName, user?.id]);
}
API Routes
app.get('/api/export', requireAuth, async (req, res) => {
if (!isEnabled('beta-export', req.user.id)) {
return res.status(403).json({ error: 'Feature not available' });
}
// Feature logic here
});
Gradual Rollout Pattern
// Start at 1%, monitor error rate, increase if healthy
const rolloutSchedule = [
{ percentage: 1, waitHours: 1 },
{ percentage: 10, waitHours: 4 },
{ percentage: 25, waitHours: 12 },
{ percentage: 50, waitHours: 24 },
{ percentage: 100, waitHours: 0 },
];
Third-Party Options
When you need advanced features (analytics, A/B testing, team management):
- LaunchDarkly — enterprise-grade, expensive
- Flagsmith — open source, self-hostable
- Growthbook — built-in A/B testing
For most indie projects, a database-backed solution covers 95% of needs.
Feature flags are included in the AI SaaS Starter Kit — database-backed, per-user rollout, React hooks. $99 one-time at whoffagents.com.
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