AWS: Giving Permission to S3 Using Canonical ID

Amazon S3 (Simple Storage Service) is a highly scalable object storage service provided by Amazon Web Services (AWS). When it comes to securing access to S3 buckets and objects, AWS offers multiple methods. One of the powerful and flexible ways is to use Canonical IDs to grant permissions. A Canonical ID is a unique identifier for an AWS account. By using Canonical IDs, you can precisely control who can access your S3 resources, making it an essential tool for fine - grained access management in S3.

Table of Contents#

  1. Core Concepts
  2. Typical Usage Scenarios
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. FAQ
  7. References

Article#

Core Concepts#

Canonical ID#

A Canonical ID is a long, alphanumeric string that uniquely identifies an AWS account. It serves as a stable identifier, unlike an AWS account ID which can be more human - readable but might not be as reliable for access control. You can find your account's Canonical ID in the AWS S3 console under the "Permissions" tab of a bucket.

S3 Bucket Policies and ACLs#

AWS S3 provides two main mechanisms for access control: Bucket Policies and Access Control Lists (ACLs).

  • Bucket Policies: These are JSON - based documents that allow you to define permissions for an entire bucket or specific prefixes within a bucket. You can use Canonical IDs in bucket policies to grant or deny access to other AWS accounts.
  • ACLs: Access Control Lists are an older access control mechanism. They are more granular at the object - level and can also use Canonical IDs to specify who has access to read, write, or perform other actions on objects.

Typical Usage Scenarios#

Cross - Account Access#

One of the most common scenarios is when you need to share S3 resources between different AWS accounts. For example, a development account might need access to a production account's S3 bucket to retrieve configuration files. By using the Canonical ID of the development account in the production bucket's policy, you can grant the necessary access.

Third - Party Integration#

If your organization works with third - party service providers, you can use Canonical IDs to give them access to specific S3 buckets. This allows you to maintain strict control over who can access your data while still enabling the required integrations.

Common Practices#

Using Bucket Policies#

To use a Canonical ID in a bucket policy, you first need to obtain the Canonical ID of the account you want to grant access to. Then, you can add a statement to your bucket policy like this:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "GrantAccessToAnotherAccount",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::111122223333:root"
            },
            "Action": [
                "s3:GetObject",
                "s3:ListBucket"
            ],
            "Resource": [
                "arn:aws:s3:::your - bucket - name/*",
                "arn:aws:s3:::your - bucket - name"
            ]
        }
    ]
}

In the Principal section, you can replace the example ARN with the Canonical ID of the target account.

Updating ACLs#

If you prefer to use ACLs, you can use the AWS CLI or SDKs to update the ACL of an object or a bucket. For example, using the AWS CLI:

aws s3api put - bucket - acl --bucket your - bucket - name --grant - read uri=http://acs.amazonaws.com/groups/global/AllUsers

You can replace the uri with the Canonical ID of the account you want to grant access to.

Best Practices#

Least Privilege Principle#

Always follow the principle of least privilege. Only grant the minimum set of permissions necessary for the account to perform its tasks. For example, if an account only needs to read objects from a bucket, don't grant write or delete permissions.

Regularly Review Permissions#

Periodically review the permissions granted using Canonical IDs. As your organization's needs change, some accounts might no longer require access, and you should revoke those permissions to enhance security.

Use IAM Roles Instead of Root Accounts#

Instead of using the root account's Canonical ID, create IAM roles with the necessary permissions and use the Canonical ID associated with the IAM role. This provides better control and security as IAM roles can be easily managed and revoked.

Conclusion#

Using Canonical IDs to give permission to S3 is a powerful and flexible way to manage access to your AWS S3 resources. It allows for cross - account access and third - party integrations while maintaining strict control over who can access your data. By understanding the core concepts, typical usage scenarios, common practices, and best practices, software engineers can effectively use Canonical IDs to secure their S3 buckets and objects.

FAQ#

What is the difference between an AWS account ID and a Canonical ID?#

An AWS account ID is a 12 - digit number that is more human - readable and used for general identification of an AWS account. A Canonical ID is a long, alphanumeric string that serves as a unique and stable identifier for an AWS account, which is more suitable for access control purposes.

Can I use multiple Canonical IDs in a single bucket policy?#

Yes, you can include multiple Canonical IDs in the Principal section of a bucket policy. This allows you to grant access to multiple AWS accounts at once.

How can I find the Canonical ID of an AWS account?#

You can find the Canonical ID of your own account in the AWS S3 console under the "Permissions" tab of a bucket. For other accounts, you may need to ask the account owner to provide it.

References#

2025-10