AWS EC2 Capacity Reservation

Use EC2 Capacity Reservation where your require future EC2 capacity based on a specified set of requirements.

Unlike other EC2 Instance Reservations there is no one to three year reservation commitment, you will be billed as soon as the instance starts

When reserving EC2 capacity you must specify the Availability Zone for the EC2 instances (Limited to a single Availability Zone), the number of EC2 instances you require and any instance attributes such as the Instance Type, Operating System and Tenancy Type (e.g. Run as a shared hardware instance).