What are feature flags and how do you roll out features safely?

Feature flags let you enable/disable functionality at runtime. **Why use them:** safer releases, gradual rollouts, quick rollback (kill switch), A/B tests. **Rollout strategies:** - percentage-based canary - user/segment targeting - environment-based flags **Pitfalls:** flag debt (old flags), inconsistent state, and security (don’t expose privileged flags to clients without server enforcement).