Reactive autoscaling is a critical safety net. Demand rises, metrics spike, policies trigger, and capacity increases. But flash-crowd events, product drops, major campaigns, and limited-inventory moments do not ramp. They cliff. Users arrive at once, and reactive scaling is structurally late because “scale triggered” is only the start of the journey to usable capacity.
If your demand spike arrives faster than your system can warm up, reactive scaling will lag no matter how well you tune it. The fix is planning and verification, scaling before the event, and proving the system is ready before customers arrive.