What Are Feature Flags?

Feature flags are conditional statements that control which code paths execute. They let you deploy code to production without exposing it to users. When ready, flip the flag to release. If something breaks, flip it back — no redeployment needed. This decouples deployment from release, the foundation of continuous delivery.

Gradual Rollouts

Instead of releasing to 100% of users at once, roll out gradually. Start with 1% (internal team), expand to 10% (beta users), then 50%, then 100%. Monitor error rates and performance at each stage. If metrics degrade, pause or roll back the flag. This approach catches issues before they affect your entire user base.

Types of Feature Flags

Release flags: control feature rollout (temporary). Experiment flags: A/B testing different variations. Ops flags: kill switches for degraded systems. Permission flags: feature access by user tier or role. Each type has different lifecycle expectations — release flags should be removed quickly; ops flags may persist.

Implementation Patterns

Simple: environment variables or config files. Better: a flag service with a dashboard. Best: a dedicated platform with targeting, analytics, and audit logs. For server-side flags, evaluate on each request. For client-side, cache flag values and re-evaluate periodically. Always have default values for when the flag service is unavailable.

Feature Flag Tools

LaunchDarkly: enterprise-grade, real-time flag updates, excellent SDKs. Unleash: open-source, self-hosted, good for teams wanting control. Flagsmith: open-source with managed option. PostHog: feature flags + analytics in one platform. For small teams, PostHog's integrated approach is compelling.

Managing Feature Flag Debt

Stale flags are technical debt. Set expiration dates when creating flags. Track flag ownership — who created it, which team owns it. Automate cleanup: alert when flags are 100% rolled out for more than 2 weeks. Remove the flag, its conditional code, and the old code path. A codebase with 500 stale flags is worse than one without flags at all.

Conclusion

Feature flags are essential for modern software delivery. They reduce release risk, enable experimentation, and provide instant rollback capability. Start with simple boolean flags for your next feature, then adopt a platform as your needs grow. Just remember to clean up after yourself.