Cross-cutting
Dark launch
A dark launch ships a feature to production but leaves it disabled for users — the code runs (sometimes against real traffic, sometimes against shadow traffic) to validate behaviour under load before being turned on. Common pattern for high-risk database changes and traffic-heavy features.
Dark launching is the more disciplined cousin of feature flagging. Whereas a feature flag might gate a UI toggle, a dark launch runs the new code path against real production data and compares results (response time, error rate, output correctness) without affecting users. Amazon famously dark-launched the recommendations system: real production traffic, computing recommendations, not displaying them — for weeks — to validate accuracy before going live.