Feature flags

Feature flags let teams deploy code independently from exposing behavior. They support trunk-based development, targeted rollout, experiments, kill switches, and safer progressive delivery.

| Flag type | Use | |-----------|-----| | Release | Hide incomplete features | | Ops kill switch | Disable broken path quickly | | Experiment | A/B with metrics |

Flags are not authorization—server-side checks still enforce permissions. Long-lived flags become hidden branches in production and need lifecycle cleanup and tests for both states when risk is high.

On interviews: stale flags, test matrix burden, authorization mistakes, config latency, and flag ownership.

Common pitfalls: using flags as security; never removing old flags; shipping only the "on" path in tests.

The trade-off is delivery flexibility versus operational and testing complexity.

Checklist:

• Separate deploy from release.
• Define flag lifecycle and owners.
• Test both flag states when risk is high.
• Never substitute flags for auth checks.