Capacity Reservations in AWS PCS

You can reserve Amazon EC2 capacity in a specific Availability Zone and for a specific duration using On-Demand Capacity Reservations or EC2 Capacity Blocks to make sure that you have the necessary compute capacity available when you need it.

Note

AWS PCS supports On-Demand Capacity Reservations (ODCR) but doesn't currently support Capacity Blocks for ML.

Using ODCRs with AWS PCS

You can choose how AWS PCS consumes your reserved instances. If you create an open ODCR, any matching instances launched by AWS PCS or other processes in your account count against the reservation. With a targeted ODCR, only instances launched with the specific reservation ID count against the reservation. For time-sensitive workloads, targeted ODCRs are more common.

You can configure an AWS PCS compute node group to use a targeted ODCR by adding it to a launch template. Here are the steps to do so:

1. Create a targeted on-demand Capacity Reservation (ODCR).

2. Add the ODCR to a Capacity Reservation group.

3. Associate the Capacity Reservation group with a launch template.

4. Create or update an AWS PCS compute node group to use the launch template.

Example: Reserve and use hpc6a.48xlarge instances with a targeted ODCR

This example command creates a targeted ODCR for 32 hpc6a.48xlarge instances. To launch the reserved instances in a placement group, add --placement-group-arn to the command. You can define a stop date with --end-date and --end-date-type, otherwise the reservation will continue until it is manually terminated.

aws ec2 create-capacity-reservation \
    --instance-type hpc6a.48xlarge \
    --instance-platform Linux/UNIX \
    --availability-zone us-east-2a \
    --instance-count 32 \
    --instance-match-criteria targeted

The result from this command will be an ARN for the new ODCR. To use the ODCR with AWS PCS, it must be added to a Capacity Reservation group. This is because AWS PCS does not support individual ODCRs. For more information, see Capacity Reservation groups in the Amazon Elastic Compute Cloud User Guide.

Here is how to add the ODCR to a Capacity Reservation group named EXAMPLE-CR-GROUP.

aws resource-groups group-resources --group EXAMPLE-CR-GROUP \
    --resource-arns arn:aws:ec2:sa-east-1:123456789012:capacity-reservation/cr-1234567890abcdef1

With the ODCR created and added to a Capacity Reservation group, it can now be connected to an AWS PCS compute node group by adding it to a launch template. Here is an example launch template that references the Capacity Reservation group.

{
  "CapacityReservationSpecification": {
    "CapacityReservationResourceGroupArn": "arn:aws:resource-groups:us-east-2:123456789012:group/EXAMPLE-CR-GROUP"
  }
}

Finally, create or update an AWS PCS compute node group to use hpc6a.48xlarge instances and use the launch template that references the ODCR in its Capacity Reservation group. For a static node group, set minimum and maximum instances to the size of the reservation (32). For a dynamic node group, set the minimum instances to 0 and the maximum up to the reservation size.

This example is a simple implementation of a single ODCR that provisioned for one compute node group. But, AWS PCS supports many other designs. For example, you can subdivide a large ODCR or Capacity Reservation group among multiple compute node groups. Or, you can use ODCRs that another AWS account has created and shared with yours. The key constraint is that ODCRs always must be contained in a Capacity Reservation group.

For more information, see On-Demand Capacity Reservations and Capacity Blocks for ML in the Amazon Elastic Compute Cloud User Guide.