Emergency operations must guarantee that a specific number of EC2 instances can launch in one Availability Zone during a declared emergency, separate from buying a billing discount. Which capability reserves that capacity?

Emergency operations that must guarantee a specific number of EC2 instances can launch in one Availability Zone during a declared emergency—separate from buying a billing discount—need On-Demand Capacity Reservations. Capacity Reservations hold capacity in a chosen AZ so launches are less likely to fail for capacity reasons when the city must scale during a crisis. That is a capacity guarantee tool, not primarily a rate discount tool.

Savings Plans primarily discount eligible usage; they do not guarantee a specific AZ inventory hold. Spot Instance advisor charts show historical interruption rates; they do not reserve emergency On-Demand capacity. AWS Budgets alerts email when spend crosses thresholds; they do not reserve compute inventory. Discounting, Spot analytics, and budget alerts fail the capacity-hold requirement.

Exam caveat: Capacity Reservation ≠ automatic deepest RI discount. You can often combine reservations with RIs/Savings Plans for both capacity and price, but the stem separating "guarantee launch capacity" from "billing discount" points specifically to Capacity Reservations.

Operational check for emergency ops: reserve the minimum instances/types required for the emergency playbook in the target AZ, tag reservations for cost attribution, test launch into the reservation during drills, release or resize reservations when plans change to avoid paying for unused holds, and document which systems are covered so incident commanders know what is pre-assured.