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. Capacity Reservations mitigate against the risk of being unable to get On-Demand capacity in case there are capacity constraints. If you have strict capacity requirements, and are running business-critical workloads that require a certain level of long or short-term capacity assurance, we recommend that you create a Capacity Reservation to ensure that you always have access to Amazon EC2 capacity when you need it, for as long as you need it.

The following are some common use cases for Capacity Reservations:

  • Disaster recovery — you can reserve capacity in a different Availability Zone or Region to ensure that the capacity you need is available during a fail over event.

  • Regulatory requirements — you can use Capacity Reservations to satisfy regulatory requirements for high availability. Capacity Reservations ensure that capacity is in place to meet those requirements, even if you aren't utilizing those resources.

  • Events — you can create Capacity Reservations before your business-critical events to ensure that you can scale when you need to.

You can create Capacity Reservations at any time, without entering into a one-year or three-year term commitment. The capacity becomes available and billing starts as soon as the Capacity Reservation is provisioned in your account. When you no longer need the capacity assurance, cancel the Capacity Reservation to release the capacity and to stop incurring charges. You can also use the billing discounts offered by Savings Plans and Regional Reserved Instances to reduce the cost of a Capacity Reservation.

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.

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

  • SUSE Linux

  • Red Hat Enterprise Linux

  • RHEL with SQL Server Standard

  • RHEL with SQL Server Enterprise

  • RHEL with SQL Server Web

  • RHEL with HA

  • RHEL with HA and SQL Server Standard

  • RHEL with HA and SQL Server Enterprise

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.

Quotas

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

Limitations

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 be created in cluster placement groups. Spread and partition placement groups are not supported.

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

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