Split off available capacity from an existing Capacity Reservation

If you have available capacity in an existing Capacity Reservation that you want to assign to a specific workload or use to carry out a specific action, you can split off the available capacity into a new Capacity Reservation. For example, to partially share a Capacity Reservation with another account, you can split off some of the available capacity to create a smaller sized Capacity Reservation. The smaller sized Capacity Reservation can then be shared with the other account using AWS Resource Access Manager (AWS RAM).

When you split available capacity from an existing Capacity Reservation, a new Capacity Reservation is automatically created. The existing Capacity Reservation will be unchanged, except for the reduced total capacity from the number of instances split off. Instances that are running in the existing Capacity Reservation are not affected. You can split the existing Capacity Reservation into only one new Capacity Reservation. In order to split off the available capacity, the existing Capacity Reservation must be active and owned by your AWS account.

The new Capacity Reservation will have the same configuration as the existing Capacity Reservation except for tags. By default, the new Capacity Reservation doesn't have any tags. You can specify new tags during the split operation. The new Capacity Reservation can also be modified after it is created, if necessary.

The maximum quantity of instances to split from an existing Capacity Reservation is the size of the reservation minus one. For example, if a Capacity Reservation has a reserved capacity of 10 slots, you can split off a maximum of nine slots if all nine slots are available.

Control access for splitting Capacity Reservations using tags

You can use tags to control access to Amazon EC2 resources, including splitting available capacity from an existing Capacity Reservation to create a new Capacity Reservation. For more information, see Controlling access to AWS resources using tags in the IAM User Guide.

To control access for splitting a Capacity Reservation using tags, make sure that you specify both resource and request tags in the policy statement because IAM policies are evaluated against both the source Capacity Reservation and the newly created Capacity Reservation. The following example policy includes the ec2:ResourceTag condition key with the tag Owner=ExampleDepartment1 for the source Capacity Reservation and the ec2:RequestTag condition key with the tag stack=production for the newly created Capacity Reservation.

{
  "Statement": [
    {
      "Sid": "AllowSourceCapacityReservation",
      "Effect": "Allow",
      "Action": "ec2:CreateCapacityReservationBySplitting",
      "Resource": "arn:aws:ec2:region:account:capacity-reservation/cr-1234567890abcdef0",
      "Condition": {
        "StringEquals": {
          "ec2:ResourceTag/Owner": "ExampleDepartment1"
        }
      }
    },
    {
      "Sid": "AllowNewlyCreatedCapacityReservation",
      "Effect": "Allow",
      "Action": ["ec2:CreateCapacityReservationBySplitting", "ec2:CreateTags"],
      "Resource": "arn:aws:ec2:region:account:capacity-reservation/*",
      "Condition": {
        "StringEquals": {
          "ec2:RequestTag/stack": "production"
        }
      }
    }
  ]
}

Split off available capacity using the Amazon EC2 console or the AWS CLI

To split off available capacity from an existing Capacity Reservation and create a new Capacity Reservation, you can use the Amazon EC2 console or the AWS CLI.

Console

To split off available capacity using the console

1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

2. In the left navigation pane, choose Capacity Reservations.

3. Select an On-Demand Capacity Reservation ID that has available capacity to split.

4. Under Actions, Manage capacity, choose Split.

5. On the Split Capacity Reservation page, under Quantity to split, use the slider or type the number of available instances to split from the current reservation.

6. (Optional) Add tags for the new Capacity Reservation.

7. Review the summary, and when you're ready, choose Split.

AWS CLI

To split off available capacity using the AWS CLI

Use the create-capacity-reservation-by-splitting command. The following example creates a new Capacity Reservation by splitting off 10 instances from Capacity Reservation with an ID of cr-1234567890abcdef0.

aws ec2 create-capacity-reservation-by-splitting --source-capacity-reservation-id cr-1234567890abcdef0 --instance-count 10