Amazon EC2 introduces new capabilities that make it easy for customers to target instance launches on their On-Demand Capacity Reservations (ODCRs). On-Demand Capacity Reservations help you reserve compute capacity for your workloads in a specified Availability Zone for any duration. You can now ensure instance launches are fulfilled exclusively by ODCRs, or prefer unutilized ODCRs before falling back to On-Demand capacity.
To get started, you can specify your capacity reservation preferences for your EC2 Auto Scaling groups via the AWS Console or the AWS CLI. These preferences can also be configured using EC2 RunInstances API calls.
These features are available in both of the AWS GovCloud (US) Regions. To learn more, see the Capacity Reservations user guide and EC2 Auto Scaling user guide.
Source:: Amazon AWS