AWS CloudFront: Access Denied When Fetching Data From S3 Through OAI
Problem: You've configured AWS CloudFront to serve content from your S3 bucket, but when attempting to access files using an Origin Access Identity (OAI), you encounter an "Access Denied" error.
Simplified: Imagine you're running a website hosted on CloudFront, pulling content from your S3 storage. You've set up an OAI to control access between CloudFront and S3, but the website can't retrieve the content, resulting in an error message.
Let's Dive In:
This issue arises when the OAI doesn't have proper permissions to access the S3 bucket. It's like trying to open a locked door without the right key.
Here's an example of how this could look in code:
// CloudFront configuration
{
"Origins": {
"S3Origin": {
"DomainName": "mybucket.s3.amazonaws.com",
"OriginPath": "/myfolder/",
"CustomOriginConfig": {
"OriginProtocolPolicy": "http-only"
},
"OriginAccessIdentity": "origin-access-identity/cloudfront/YOUR-OAI-ID"
}
},
// ... rest of the CloudFront configuration
}
// S3 bucket policy
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AllowCloudFrontAccess",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::cloudfront:YOUR-ACCOUNT-ID:user/CloudFrontOriginAccessIdentityYOUR-OAI-ID"
},
"Action": [
"s3:GetObject",
"s3:GetObjectVersion"
],
"Resource": [
"arn:aws:s3:::mybucket/*"
]
}
]
}
Common Causes & Solutions:
-
Incorrect OAI in S3 Policy: The most frequent error is mismatching the OAI in the S3 bucket policy with the OAI configured in CloudFront. Double-check the 'Principal' section of your bucket policy and ensure it matches the OAI ID from your CloudFront configuration.
-
Missing Permissions: The bucket policy might be missing required actions like "s3:GetObject". Ensure you've granted sufficient permissions for the OAI to perform necessary actions on the bucket.
-
Incorrect Resource Specificity: The 'Resource' element in your S3 policy needs to match the objects you intend to access. If your CloudFront configuration specifies a particular folder or file, ensure the 'Resource' entry is accurate.
-
Account Mismatch: Ensure your CloudFront and S3 accounts are the same. If you're using a different account for CloudFront, you'll need to adjust the policy accordingly.
Debugging Tips:
- CloudFront Access Logs: Review your CloudFront access logs for detailed error messages.
- S3 Event Notifications: Enable S3 event notifications to receive alerts when access attempts are made.
- S3 Bucket Policy Simulator: Use the S3 bucket policy simulator to verify your policy's validity.
Additional Resources:
- AWS Documentation: https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/private-content-restricting-access-origin.html
- AWS Support: If you're still facing issues, consider reaching out to AWS Support for assistance.
Remember: Carefully review and test your configuration to ensure the OAI has the appropriate access to your S3 bucket. This will guarantee a smooth flow of content from your S3 bucket to your CloudFront distribution.
