AWS Key Management Service

Developer Guide

AWS Documentation » AWS KMS » Developer Guide » Limits

Limits

All AWS KMS objects have limits that apply to each region and each AWS account. If you need to exceed these limits, please visit the AWS Support Center and create a case.

Customer Master Keys (CMKs): 1000

You can have up to 1000 CMKs per region. All CMKs count towards this limit regardless of their status (enabled, disabled, or pending deletion). You can request more CMKs in a region; however, managing a large number of CMKs from the AWS Management Console may be slower than acceptable. If you have a large number of CMKs in a region, we recommend managing them programmatically with the AWS SDKs or AWS Command Line Tools.

Aliases: 1100

An alias is an independent display name that you can map to a CMK. It is not a property of a CMK. You can map multiple aliases to a single CMK, so the limit for aliases is higher than the limit for CMKs. If you request an increase in the number of CMKs, you might also need to request an increase in the number of aliases.

Grants per CMK: 2500

Using Grants are advanced mechanisms for specifying permissions that you or an AWS service integrated with AWS KMS can use to limit how and when a CMK can be used. Grants are attached to a CMK, and each grant contains the principal who receives permission to use the CMK, the ID of the CMK, and a list of operations that can be performed. Grants are an alternative to the key policy.

Each CMK can have up to 2500 grants, including the grants created by AWS services that are integrated with AWS KMS. For a list of these services, see How AWS Services use AWS KMS. One effect of this limit is that you cannot create more than 2500 resources that use the same CMK. For example, you cannot create more than 2500 encrypted EBS volumes that use the same CMK.

Grants for a given principal per CMK: 500

For a given CMK, no more than 500 grants can specify the same grantee principal. For example, assume that you want to encrypt multiple Amazon EBS volumes and attach them to a single Amazon Elastic Compute Cloud (Amazon EC2) instance. In this case, a unique grant is created for each encrypted volume and all of these grants have the same grantee principal (an IAM assumed-role user associated with the EC2 instance). Each grant gives permission to use the specified CMK to decrypt an EBS volume's unique data encryption key. For each CMK, you can have up to 500 grants that specify the same EC2 instance as the grantee principal. This effectively means that you can have no more than 500 encrypted EBS volumes per EC2 instance for a given CMK.

Requests per second: varies

AWS KMS throttles API requests at different limits depending on the API operation. Throttling means that AWS KMS rejects an otherwise valid request because the request exceeds the limit for the number of requests per second. When a request is throttled, AWS KMS returns a ThrottlingException error. The following table lists each API operation and the point at which AWS KMS throttles requests for that operation.

Shared limit

The API operations in the first row of the following table share a limit of 1200 requests per second. For example, when you make 600 GenerateDataKey and 400 Decrypt requests per second, AWS KMS doesn't throttle your requests. However, when you make 200 Encrypt and 1100 GenerateDataKey requests per second, AWS KMS throttles your requests because you are making more than 1200 requests per second for operations with the shared limit.

The remaining API operations have a unique limit for requests per second, which means the limit is not shared.

API requests made on your behalf

You can make API requests directly or by using an integrated AWS service that makes API requests to AWS KMS on your behalf. The limit applies to both kinds of requests.

For example, you might store data in Amazon S3 using server-side encryption with AWS KMS (SSE-KMS). Each time you upload or download an S3 object that's encrypted with SSE-KMS, Amazon S3 makes a GenerateDataKey (for uploads) or Decrypt (for downloads) request to AWS KMS on your behalf. These requests count toward your limit, so AWS KMS throttles the requests if you exceed a combined total of 1200 uploads or downloads per second of S3 objects encrypted with SSE-KMS.

Cross-account requests

When an application in one AWS account uses a CMK owned by a different account, that's known as a cross-account request. For cross-account requests, AWS KMS throttles the account that makes the requests, not the account that owns the CMK. For example, you might have applications in accounts A and B that both use a CMK in account C. In this scenario, the limit for requests per second applies separately to accounts A and B, not to account C.

On this page:

• Customer Master Keys (CMKs): 1000
• Aliases: 1100
• Grants per CMK: 2500
• Grants for a given principal per CMK: 500
• Requests per second: varies