This post is written by Yi-Kang Wang, Senior Hybrid Specialist SA.

AWS Outposts rack is a fully managed service that delivers the same AWS infrastructure, AWS services, APIs, and tools to virtually any on-premises datacenter or co-location space for a truly consistent hybrid experience. AWS Outposts rack is ideal for workloads that require low latency access to on-premises systems, local data processing, data residency, and migration of applications with local system interdependencies. In addition to these benefits, we have started to see many of you need to share Outposts rack resources across business units and projects within your organization. This blog post will discuss how you can share Outposts rack resources by creating computing quotas on Outposts with Amazon Elastic Compute Cloud (Amazon EC2) Capacity Reservations sharing.

In AWS Regions, you can set up and govern a multi-account AWS environment using AWS Organizations and AWS Control Tower. The natural boundaries of accounts provide some built-in security controls, and AWS provides additional governance tooling to help you achieve your goals of managing a secure and scalable cloud environment. And while Outposts can consistently use organizational structures for security purposes, Outposts introduces another layer to consider in designing that structure. When an Outpost is shared within an Organization, the utilization of the purchased capacity also needs to be managed and tracked within the organization. The account that owns the Outpost resource can use AWS Resource Access Manager (RAM) to create resource shares for member accounts within their organization. An Outposts administrator (admin) can share the ability to launch instances on the Outpost itself, access to the local gateways (LGW) route tables, and/or access to customer-owned IPs (CoIP). Once the Outpost capacity is shared, the admin needs a mechanism to control the usage and prevent over utilization by individual accounts. With the introduction of Capacity Reservations on Outposts, we can now set up a mechanism for computing quotas.

Concept of computing quotas on Outposts rack

In the AWS Regions, Capacity Reservations enable you to reserve compute capacity for your Amazon EC2 instances in a specific Availability Zone for any duration you need. On May 24, 2021, Capacity Reservations were enabled for Outposts rack. It supports not only EC2 but Outposts services running over EC2 instances such as Amazon Elastic Kubernetes (EKS), Amazon Elastic Container Service (ECS) and Amazon EMR. The computing power of above services could be covered in your resource planning as well. For example, you’d like to launch an EKS cluster with two self-managed worker nodes for high availability. You can reserve two instances with Capacity Reservations to secure computing power for the requirement.

Here I’ll describe a method for thinking about resource pools that an admin can use to manage resource allocation. I’ll use three resource pools, that I’ve named reservation pool, bulk and attic, to effectively and extensibly manage the Outpost capacity.

A reservation pool is a resource pool reserved for a specified member account. An admin creates a Capacity Reservation to match member account’s need, and shares the Capacity Reservation with the member account through AWS RAM.

A bulk pool is an unreserved resource pool that is used when member accounts run out of compute capacity such as EC2, EKS, or other services using EC2 as underlay. All compute capacity in the bulk pool can be requested to launch until it is exhausted. Compute capacity that is not under a reservation pool belongs to the bulk pool by default.

An attic is a resource pool created to hold the compute capacity that the admin wouldn’t like to share with member accounts. The compute capacity remains in control by admin, and can be released to the bulk pool when needed. Admin creates a Capacity Reservation for the attic and owns the Capacity Reservation.

The following diagram shows how the admin uses Capacity Reservations with AWS RAM to manage computing quotas for two member accounts on an Outpost equipped with twenty-four m5.xlarge. Here, I’m going to break the idea into several pieces to help you understand easily.

  1. There are three Capacity Reservations created by admin. CR #1 reserves eight m5.xlarge for the attic, CR #2 reserves four m5.xlarge instances for account A and CR #3 reserves six m5.xlarge instances for account B.
  2. The admin shares Capacity Reservation CR #2 and CR #3 with account A and B respectively.
  3. Since eighteen m5.xlarge instances are reserved, the remaining compute capacity in the bulk pool will be six m5.xlarge.
  4. Both Account A and B can continue to launch instances exceeding the amount in their Capacity Reservation, by utilizing the instances available to everyone in the bulk pool.

Concept of defining computing quotas

  1. Once the bulk pool is exhausted, account A and B won’t be able to launch extra instances from the bulk pool.
  2. The admin can release more compute capacity from the attic to refill the bulk pool, or directly share more capacity with CR#2 and CR#3. The following diagram demonstrates how it works.

Concept of refilling bulk pool

Based on this concept, we realize that compute capacity can be securely and efficiently allocated among multiple AWS accounts. Reservation pools allow every member account to have sufficient resources to meet consistent demand. Making the bulk pool empty indirectly sets the maximum quota of each member account. The attic plays as a provider that is able to release compute capacity into the bulk pool for temporary demand. Here are the major benefits of computing quotas.

  • Centralized compute capacity management
  • Reserving minimum compute capacity for consistent demand
  • Resizable bulk pool for temporary demand
  • Limiting maximum compute capacity to avoid resource congestion.

Configuration process

To take you through the process of configuring computing quotas in the AWS console, I have simplified the environment like the following architecture. There are four m5.4xlarge instances in total. An admin account holds two of the m5.4xlarge in the attic, and a member account gets the other two m5.4xlarge for the reservation pool, which results in no extra instance in the bulk pool for temporary demand.


  • The admin and the member account are within the same AWS Organization.
  • The Outpost ID, LGW and CoIP have been shared with the member account.

Architecture for configuring computing quotas

  1. Creating a Capacity Reservation for the member account

Sign in to AWS console of the admin account and navigate to the AWS Outposts page. Select the Outpost ID you want to share with the member account, choose Actions, and then select Create Capacity Reservation. In this case, reserve two m5.4xlarge instances.

Create a capacity reservation

In the Reservation details, you can terminate the Capacity Reservation by manually enabling or selecting a specific time. The first option of Instance eligibility will automatically count the number of instances against the Capacity Reservation without specifying a reservation ID. To avoid misconfiguration from member accounts, I suggest you select Any instance with matching details in most use cases.

Reservation details

  1. Sharing the Capacity Reservation through AWS RAM

Go to the RAM page, choose Create resource share under Resource shares page. Search and select the Capacity Reservation you just created for the member account.

Specify resource sharing details

Choose a principal that is an AWS ID of the member account.

Choose principals that are allowed to access

  1. Creating a Capacity Reservation for attic

Create a Capacity Reservation like step 1 without sharing with anyone. This reservation will just be owned by the admin account. After that, check Capacity Reservations under the EC2 page, and the two Capacity Reservations there, both with availability of two m5.4xlarge instances.

3.	Creating a Capacity Reservation for attic

  1. Launching EC2 instances

Log in to the member account, select the Outpost ID the admin shared in step 2 then choose Actions and select Launch instance. Follow AWS Outposts User Guide to launch two m5.4xlarge on the Outpost. When the two instances are in Running state, you can see a Capacity Reservation ID on Details page. In this case, it’s cr-0381467c286b3d900.

Create EC2 instances

So far, the member account has run out of two m5.4xlarge instances that the admin reserved for. If you try to launch the third m5.4xlarge instance, the following failure message will show you there is not enough capacity.

Launch status

  1. Allocating more compute capacity in bulk pool

Go back to the admin console, select the Capacity Reservation ID of the attic on EC2 page and choose Edit. Modify the value of Quantity from 2 to 1 and choose Save, which means the admin is going to release one more m5.4xlarge instance from the attic to the bulk pool.

Instance details

  1. Launching more instances from bulk pool

Switch to the member account console, and repeat step 4 but only launch one more m5.4xlarge instance. With the resource release on step 5, the member account successfully gets the third instance. The compute capacity is coming from the bulk pool, so when you check the Details page of the third instance, the Capacity Reservation ID is blank.

6.	Launching more instances from bulk pool

Cleaning up

  1. Terminate the three EC2 instances in the member account.
  2. Unshare the Capacity Reservation in RAM and delete it in the admin account.
  3. Unshare the Outpost ID, LGW and CoIP in RAM to get the Outposts resources back to the admin.


In this blog post, the admin can dynamically adjust compute capacity allocation on Outposts rack for purpose-built member accounts with an AWS Organization. The bulk pool offers an option to fulfill flexibility of resource planning among member accounts if the maximum instance need per member account is unpredictable. By contrast, if resource forecast is feasible, the admin can revise both the reservation pool and the attic to set a hard limit per member account without using the bulk pool. In addition, I only showed you how to create a Capacity Reservation of m5.4xlarge for the member account, but in fact an admin can create multiple Capacity Reservations with various instance types or sizes for a member account to customize the reservation pool. Lastly, if you would like to securely share Amazon S3 on Outposts with your member accounts, check out Amazon S3 on Outposts now supports sharing across multiple accounts to get more details.