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Terraform

AccessDenied: Fix CopyObject Errors in [Platform]

By Ondřej Dolanský on 01/07/2025

Learn how to troubleshoot and resolve the frustrating "AccessDenied" error when using the CopyObject function in your cloud storage applications.

AccessDenied: Fix CopyObject Errors in [Platform]

Table of Contents

Introduction

Encountering "AccessDenied" errors while using the AWS S3 CopyObject operation can be frustrating. This guide will walk you through the most common causes and solutions to help you get your data copied successfully. We'll cover essential areas like bucket permissions, object tagging considerations, VPC endpoint limitations, AWS CLI configuration checks, and CloudFormation permission setups. Let's dive in and resolve those access issues!

Step-by-Step Guide

Let's break down how to troubleshoot "AccessDenied" errors when using the AWS S3 CopyObject operation.

1. Bucket Permissions

  • Same Account: Ensure the IAM role or user performing the copy has both s3:GetObject permission on the source bucket and s3:PutObject permission on the destination bucket.

    {
    "Effect": "Allow",
    "Action": [
        "s3:GetObject",
        "s3:PutObject"
    ],
    "Resource": [
        "arn:aws:s3:::source-bucket/*",
        "arn:aws:s3:::destination-bucket/*"
    ]
}

  • Cross Account: You'll need explicit permissions from the source account granting the copying account access. Bucket policies or cross-account IAM roles are common solutions.

2. Object Tagging

  • If you're copying objects with tags, ensure your permissions include s3:GetObjectTagging for the source and s3:PutObjectTagging for the destination.

3. VPC Endpoints

  • Cross-Region Copies: VPC endpoints don't support copying objects across AWS regions. Use a public endpoint or set up appropriate routing.

4. AWS CLI Configuration

  • Verify your AWS CLI is configured with the correct credentials and region. Misconfigured profiles can lead to "AccessDenied" errors.

5. CloudFormation

  • If using CloudFormation, double-check the IAM role assigned to your stack has the necessary S3 permissions.

Debugging Tips

  • Error Messages: Carefully examine the "AccessDenied" error message for clues. It often specifies the missing permission.
  • AWS CloudTrail: Enable CloudTrail logs for your S3 buckets to track API calls and identify the source of authorization failures.

Code Example

This Python code demonstrates how to troubleshoot "AccessDenied" errors during S3 CopyObject operations. It covers two scenarios: copying within the same AWS account and copying across different accounts. Each scenario includes code examples and solutions to resolve the error. The code showcases how to use the AWS SDK for Python (Boto3) to perform the copy operation and handle exceptions. It also emphasizes the importance of checking error messages and utilizing AWS CloudTrail for debugging. The provided solutions involve granting necessary permissions through IAM policies or bucket policies, ensuring the user or role executing the code has appropriate access to both the source and destination S3 buckets. The code highlights security best practices, such as granting least privilege access and adapting the examples to specific use cases.

This example demonstrates common scenarios and solutions for "AccessDenied" errors.

Scenario 1: Same Account Copy with Insufficient Permissions

import boto3

s3 = boto3.client('s3')

source_bucket = 'your-source-bucket'
source_key = 'your-source-object'
destination_bucket = 'your-destination-bucket'
destination_key = 'your-destination-object'

try:
    s3.copy_object(
        CopySource={'Bucket': source_bucket, 'Key': source_key},
        Bucket=destination_bucket,
        Key=destination_key
    )
    print("Object copied successfully.")
except s3.exceptions.ClientError as e:
    if e.response['Error']['Code'] == 'AccessDenied':
        print("Access Denied: ", e.response['Error']['Message'])
    else:
        raise e

# Solution: Attach an IAM policy to the user or role executing this code with the following permissions:
# {
#     "Effect": "Allow",
#     "Action": [
#         "s3:GetObject",
#         "s3:PutObject"
#     ],
#     "Resource": [
#         f"arn:aws:s3:::{source_bucket}/*",
#         f"arn:aws:s3:::{destination_bucket}/*"
#     ]
# }

Scenario 2: Cross-Account Copy with Missing Source Account Permissions

import boto3

# Assume you are executing this code from Account B, trying to copy from Account A
source_bucket = 'source-bucket-in-account-a'
source_key = 'your-source-object'
destination_bucket = 'your-destination-bucket'
destination_key = 'your-destination-object'

s3 = boto3.client('s3')

try:
    s3.copy_object(
        CopySource={'Bucket': source_bucket, 'Key': source_key},
        Bucket=destination_bucket,
        Key=destination_key,
        ACL='bucket-owner-full-control'  # Grant ownership to the destination bucket owner
    )
    print("Object copied successfully.")
except s3.exceptions.ClientError as e:
    if e.response['Error']['Code'] == 'AccessDenied':
        print("Access Denied: ", e.response['Error']['Message'])
    else:
        raise e

# Solution: In Account A (source account), create a bucket policy or use a cross-account IAM role to grant Account B 
# permission to GetObject from the source bucket.

Debugging Tips:

  • Error Messages: The e.response['Error']['Message'] in the examples above provides valuable information about the denied permission.
  • AWS CloudTrail: Enable CloudTrail data events for your S3 buckets. Analyze the logs to see the exact API call made, the caller's identity, and the reason for the access denial.

Remember:

  • Replace placeholder values with your actual bucket names, object keys, and account IDs.
  • This code provides a starting point. Adapt it to your specific use case and error messages.
  • Always follow AWS security best practices and grant least privilege access.

Additional Notes

General Considerations:

  • Root User: Avoid using the AWS root user for S3 operations. It's best practice to create IAM users or roles with specific permissions.
  • Least Privilege: Always follow the principle of least privilege. Grant only the necessary permissions required to perform the copy operation.
  • Policy Evaluation Logic: Remember that AWS evaluates policies from multiple sources (identity-based and resource-based). An "AccessDenied" error could result from an explicit deny, even if an allow exists.
  • Object Ownership: When copying objects across accounts, the destination bucket owner becomes the object owner by default. You might need to adjust object ACLs or use specific copy options to manage ownership.
  • Encryption: If your objects are encrypted, ensure your IAM policies include permissions for the relevant encryption keys (e.g., using AWS KMS).

Additional Troubleshooting Steps:

  • Test with the AWS CLI: If you're having trouble with SDKs, try performing the copy operation using the AWS CLI. This can help isolate whether the issue is with your code or permissions.
  • Check for Typos: Double-check your bucket names, object keys, region names, and ARN values for any typos.
  • Temporary Credentials: If you're using temporary credentials (e.g., from AWS STS), ensure they are valid and have not expired.
  • Contact AWS Support: If you've exhausted all troubleshooting steps and are still unable to resolve the "AccessDenied" error, consider contacting AWS Support for further assistance.

Proactive Measures:

  • Automated Testing: Implement automated tests for your S3 copy operations to catch permission issues early in the development cycle.
  • Infrastructure as Code: Manage your IAM policies and S3 bucket configurations using infrastructure-as-code tools like CloudFormation or Terraform. This helps ensure consistency and makes it easier to track changes.
  • Security Auditing: Regularly audit your S3 bucket policies and IAM permissions to identify and remediate any potential security risks.

Summary

Issue Area Potential Cause Solution
Bucket Permissions Lack of s3:GetObject on source bucket or s3:PutObject on destination bucket for the copying entity (IAM user/role). Grant the required permissions via IAM policies. For cross-account copies, use bucket policies or cross-account IAM roles.
Object Tagging Missing s3:GetObjectTagging (source) and s3:PutObjectTagging (destination) permissions when copying tagged objects. Include these permissions in the relevant IAM policies.
VPC Endpoints Attempting cross-region copies using VPC endpoints. Use public endpoints or configure appropriate routing for cross-region access.
AWS CLI Configuration Incorrect AWS CLI configuration (credentials, region). Verify and correct the AWS CLI profile settings.
CloudFormation Insufficient S3 permissions for the CloudFormation stack's IAM role. Update the stack's IAM role to include the necessary S3 permissions.

Debugging Tools:

  • Error Messages: Analyze the "AccessDenied" message for specific missing permissions.
  • AWS CloudTrail: Enable CloudTrail logging for S3 buckets to track API calls and identify authorization failures.

Conclusion

Troubleshooting "AccessDenied" errors when using AWS S3 CopyObject can be streamlined by systematically addressing common causes. Start by verifying bucket permissions, ensuring the copying entity has appropriate s3:GetObject and s3:PutObject permissions. Consider object tagging requirements, adding s3:GetObjectTagging and s3:PutObjectTagging permissions if needed. Remember that VPC endpoints have limitations with cross-region copies; use public endpoints or configure routing accordingly. Confirm your AWS CLI configuration, including credentials and region, to prevent misconfiguration issues. When using CloudFormation, double-check the stack's IAM role for necessary S3 permissions. Leverage debugging tools like error messages, which often pinpoint missing permissions, and AWS CloudTrail for detailed API call tracking. By following these steps, you can efficiently diagnose and resolve "AccessDenied" errors, ensuring smooth data copying operations within your S3 environment.

References

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