What is Capacity Reservation?
Capacity Reservation is an AWS feature that lets you reserve physical EC2 compute capacity in a specific Availability Zone for any duration.
Unlike Reserved Instances, its primary purpose is a hardware guarantee rather than a financial discount. It ensures that you will never receive an "Insufficient Instance Capacity" error when launching critical workloads, regardless of market demand.
You pay the standard On-Demand rate for the reserved slot whether your instance is actively running in it or sitting idle.