On-Demand Capacity Reservations - Amazon Elastic Compute Cloud

On-Demand Capacity Reservations

On-Demand Capacity Reservations enable you to reserve compute capacity for your Amazon EC2 instances in a specific Availability Zone for any duration. This gives you the ability to create and manage Capacity Reservations independently from the billing discounts offered by Savings Plans or Regional Reserved Instances.

By creating Capacity Reservations, you ensure that you always have access to EC2 capacity when you need it, for as long as you need it. You can create Capacity Reservations at any time, without entering into a one-year or three-year term commitment, and the capacity is available immediately. Billing starts as soon as the capacity is provisioned and the Capacity Reservation enters the active state. When you no longer need it, cancel the Capacity Reservation to stop incurring charges.

When you create a Capacity Reservation, you specify:

  • The Availability Zone in which to reserve the capacity

  • The number of instances for which to reserve capacity

  • The instance attributes, including the instance type, tenancy, and platform/OS

Capacity Reservations can only be used by instances that match their attributes. By default, they are automatically used by running instances that match the attributes. If you don't have any running instances that match the attributes of the Capacity Reservation, it remains unused until you launch an instance with matching attributes.

In addition, you can use Savings Plans and Regional Reserved Instances with your Capacity Reservations to benefit from billing discounts. AWS automatically applies your discount when the attributes of a Capacity Reservation match the attributes of a Savings Plan or Regional Reserved Instance. For more information, see Billing discounts.

Differences between Capacity Reservations, Reserved Instances, and Savings Plans

The following table highlights key differences between Capacity Reservations, Reserved Instances, and Savings Plans:

Capacity Reservations Zonal Reserved Instances Regional Reserved Instances Savings Plans
Term No commitment required. Can be created and canceled as needed. Requires a fixed one-year or three-year commitment
Capacity benefit Capacity reserved in a specific Availability Zone. No capacity reserved.
Billing discount No billing discount. † Provides a billing discount.
Instance Limits Your On-Demand Instance limits per Region apply. Default is 20 per Availability Zone. You can request a limit increase. Default is 20 per Region. You can request a limit increase. No limit.

† You can combine Capacity Reservations with Savings Plans or Regional Reserved Instances to receive a discount.

For more information, see the following:

Supported platforms

You must create the Capacity Reservation with the correct platform to ensure that it properly matches with your instances. Capacity Reservations support the following platforms:

  • Linux/UNIX

  • Linux with SQL Server Standard

  • Linux with SQL Server Web

  • Linux with SQL Server Enterprise

  • Red Hat Enterprise Linux

  • SUSE Linux

When you purchase a Capacity Reservation, you must specify the platform that represents the operating system for your instance.

  • For SUSE Linux and RHEL distributions, excluding BYOL, you must choose the specific platform. For example, the SUSE Linux or Red Hat Enterprise Linux platform.

  • For all other Linux distributions (including Ubuntu), choose the Linux/UNIX platform.

  • If you bring your existing RHEL subscription (BYOL), you must choose the Linux/UNIX platform.

For more information about the supported Windows platforms, see Supported platforms in the Amazon EC2 User Guide for Windows Instances.

Capacity Reservation limits

The number of instances for which you are allowed to reserve capacity is based on your account's On-Demand Instance limit. You can reserve capacity for as many instances as that limit allows, minus the number of instances that are already running.

Capacity Reservation limitations and restrictions

Before you create Capacity Reservations, take note of the following limitations and restrictions.

  • Active and unused Capacity Reservations count toward your On-Demand Instance limits.

  • Capacity Reservations are not transferable from one AWS account to another. However, you can share Capacity Reservations with other AWS accounts. For more information, see Work with shared Capacity Reservations.

  • Zonal Reserved Instance billing discounts do not apply to Capacity Reservations.

  • Capacity Reservations can't be created in placement groups.

  • Capacity Reservations can't be used with Dedicated Hosts.

  • Capacity Reservations do not ensure that a hibernated instance can resume after you try to start it.