Are File Permissions Preserved Across AWS Accounts S3 Copy?

Amazon S3 (Simple Storage Service) is a highly scalable and reliable object storage service provided by Amazon Web Services (AWS). In many enterprise scenarios, there is a need to copy objects between different AWS accounts. One crucial question that often arises is whether file permissions are preserved during such cross - account S3 copy operations. Understanding this behavior is essential for software engineers to ensure proper data security and access control when managing data across multiple AWS accounts.

Table of Contents#

  1. Core Concepts
    • Amazon S3 File Permissions
    • Cross - Account S3 Copy
  2. Typical Usage Scenarios
    • Data Migration
    • Data Sharing
  3. Common Practice
    • Using AWS CLI
    • Using AWS SDKs
  4. Best Practices
    • Pre - Copy Permission Review
    • Post - Copy Permission Verification
  5. Conclusion
  6. FAQ
  7. References

Article#

Core Concepts#

Amazon S3 File Permissions#

In Amazon S3, file permissions are used to control who can access and perform operations on objects stored in buckets. There are two main types of permissions:

  • Bucket Policies: These are JSON - based access policies that are attached to an S3 bucket. They can be used to grant or deny access to the entire bucket or specific prefixes within it. For example, a bucket policy can be configured to allow access only from a specific IP range.
  • Access Control Lists (ACLs): ACLs are an older way of managing object - level and bucket - level permissions. Each object and bucket has an associated ACL that defines which AWS accounts or groups have specific permissions, such as read, write, or full control.

Cross - Account S3 Copy#

Cross - account S3 copy refers to the process of copying objects from an S3 bucket in one AWS account to an S3 bucket in another AWS account. This can be achieved using various AWS tools and APIs, such as the AWS CLI, AWS SDKs, or AWS Management Console. Before performing a cross - account copy, appropriate permissions need to be set up to allow the source account to access the destination bucket and vice versa.

Typical Usage Scenarios#

Data Migration#

One common scenario is when a company is consolidating its data from multiple AWS accounts into a single account for better management and cost control. For example, a large enterprise may have different departments using separate AWS accounts, and they want to centralize their data in a single data lake account. In this case, they need to copy objects from the departmental accounts to the central account while ensuring that the appropriate access controls are maintained.

Data Sharing#

Another scenario is data sharing between different business units or partners. A company may want to share certain datasets with its partners while maintaining strict control over who can access and modify the data. By copying objects across accounts, the company can provide access to the necessary data while keeping the original data secure in its own account.

Common Practice#

Using AWS CLI#

The AWS CLI is a powerful tool for performing cross - account S3 copy operations. Here is an example of how to copy an object from a source bucket in one account to a destination bucket in another account:

aws s3 cp s3://source - bucket/object - key s3://destination - bucket/object - key \
  --source - profile source - account - profile \
  --profile destination - account - profile

In this example, source - account - profile and destination - account - profile are the AWS CLI profiles configured for the source and destination accounts respectively.

Using AWS SDKs#

AWS SDKs provide a programmatic way to perform cross - account S3 copy operations. Here is a simple example using the Python AWS SDK (Boto3):

import boto3
 
# Create S3 clients for source and destination accounts
source_session = boto3.Session(profile_name='source - account - profile')
source_s3 = source_session.client('s3')
 
destination_session = boto3.Session(profile_name='destination - account - profile')
destination_s3 = destination_session.client('s3')
 
# Copy the object
source_bucket = 'source - bucket'
source_key = 'object - key'
destination_bucket = 'destination - bucket'
destination_key = 'object - key'
 
destination_s3.copy_object(
    CopySource={
        'Bucket': source_bucket,
        'Key': source_key
    },
    Bucket=destination_bucket,
    Key=destination_key
)

Best Practices#

Pre - Copy Permission Review#

Before performing a cross - account S3 copy, it is essential to review the permissions on both the source and destination buckets. Ensure that the source account has the necessary read permissions to access the objects and that the destination account has the appropriate write permissions to receive the copied objects. Also, review the bucket policies and ACLs to understand the existing access controls.

Post - Copy Permission Verification#

After the copy operation is complete, verify that the permissions on the copied objects in the destination bucket are as expected. Check the bucket policies and ACLs associated with the destination bucket and the objects to ensure that the access controls are consistent with the source objects. This can help prevent any unauthorized access to the copied data.

Conclusion#

When performing a cross - account S3 copy, file permissions are not automatically preserved. The copied objects in the destination bucket will inherit the default permissions of the destination bucket, unless specific steps are taken to set the appropriate permissions. Software engineers need to be aware of this behavior and follow best practices such as pre - copy permission review and post - copy permission verification to ensure proper data security and access control.

FAQ#

Q1: Can I preserve the exact same permissions on the copied objects?#

A1: By default, no. However, you can use AWS SDKs or custom scripts to set the permissions on the copied objects to match the source objects.

Q2: Do I need to set up cross - account IAM roles for the copy operation?#

A2: Yes, you need to set up appropriate IAM roles with the necessary permissions to allow the source account to access the destination bucket and vice versa.

Q3: What if I forget to review the permissions before the copy operation?#

A3: There is a risk of data being copied to the destination bucket with incorrect or overly permissive access controls, which can lead to security vulnerabilities. It is important to review and set the permissions correctly before performing the copy.

References#

2025-10