Capacity Reservations
- What it is
- On-Demand Capacity Reservations reserve EC2 capacity in a specific Availability Zone for any duration.
- Guarantees the capacity is there when you need to launch.
- Key nuance: no discount
- You pay the On-Demand rate whether or not you actually run instances in the reservation.
- To get a discount, combine it with a Savings Plan or a regional Reserved Instance.
- When to use
- Business-critical events, disaster recovery failover capacity, regulatory requirements to guarantee availability.
- The three-way distinction
- Capacity Reservation → capacity guarantee, no discount.
- Savings Plan / RI → discount, no capacity guarantee (except zonal RIs).
- Zonal RI → both, but locked to one AZ and one configuration.