NoSuchKey Error: "The specified key does not exist" for S3 Object

The NoSuchKey error you're experiencing could be due to a few different factors, but it's important to note that this error typically indicates that the specified object does not exist in the S3 bucket at the time of the request.

Given the context you've provided, here are a few possibilities to consider:

1. Eventual Consistency: Although S3 is generally strongly consistent for most operations, there are still some scenarios where eventual consistency can come into play. If you've recently made changes to your bucket or objects, it's possible that the changes haven't fully propagated across all of Amazon's systems yet. This could lead to temporary NoSuchKey errors, especially if you're accessing objects from different regions or availability zones.

2. Permissions: The error could be related to permissions. If your IAM policies or bucket policies have changed, or if the object's ACL has been modified, you might receive a NoSuchKey error instead of an Access Denied error. This is because S3 doesn't always distinguish between non-existent objects and objects you don't have permission to access.

3. Object Key Issues: Ensure that the object key you're using to access the file is correct. S3 object keys are case-sensitive and must match exactly. Also, check for any unexpected characters or encoding issues in the key name.

4. Bucket Versioning: If you have versioning enabled on your bucket, make sure you're requesting the correct version of the object. The latest version might have been deleted, leaving only older versions.

5. CloudFront Configuration: Although you mentioned that CloudFront is working fine, it's worth double-checking your CloudFront distribution settings. Ensure that the origin path and behaviors are correctly configured to point to the right S3 bucket and objects.

6. S3 Replication Issues: If you're using S3 replication, there might be a delay or issue with the replication process, causing objects to appear missing in certain regions.

To troubleshoot this issue:

1. Double-check your object keys and ensure they're correct.
2. Verify your IAM and bucket policies to ensure you have the necessary permissions.
3. Try accessing the objects from a different region or after a short delay to rule out consistency issues.
4. Use the AWS CLI or SDK to list the contents of your bucket and verify the objects are present.
5. Check your CloudFront configuration to ensure it's correctly set up with your S3 bucket.

If the issue persists after these checks, it would be advisable to contact AWS Support for further assistance, as they can provide more detailed insights into your specific account and configuration.
Sources
Why Does S3 Return 403 Instead of 404 When the Object Doesn’t Exist? | AWS re:Post
Error responses - Amazon Simple Storage Service
Community | Now You See Me, Now You Don't - the Mystery of the Vanishing S3 Objects
Community | Now You See Me, Now You Don't - the Mystery of the Vanishing S3 Objects
Naming Amazon S3 objects - Amazon Simple Storage Service