S3 CRR Replication object versioning issue

There are several potential reasons why some objects might not be replicating in your S3 Cross-Region Replication (CRR) setup. Let's explore some possibilities and solutions:

1. Pre-existing objects: Objects that existed in your source bucket before you set up the replication rule are not automatically replicated. S3 doesn't replicate objects retroactively. To replicate these pre-existing objects, you would need to use S3 Batch Replication or manually copy them to trigger replication.

2. Replication configuration: Verify your replication configuration on the source bucket. Ensure that:

   • The destination bucket's ARN is correct
   • Any key name prefixes or tags you've specified are accurate
   • The replication rule status is set to "Enabled"

3. Object size and replication time: The time it takes to replicate an object depends on factors like the distance between regions and the object size. Large objects may take longer to replicate. Check the replication status of the objects in question. If the status is "PENDING", S3 hasn't completed the replication yet.

4. Replication failures: If an object's replication status is "FAILED", there might be issues with permissions or the replication configuration. Review your IAM roles and policies to ensure S3 has the necessary permissions to read from the source bucket and write to the destination bucket.

5. Versioning: Ensure that versioning is enabled on both the source and destination buckets. Only new versions of objects created after enabling replication will be replicated.

6. Encryption: If you're using server-side encryption with AWS KMS, make sure the IAM role has permissions to use the KMS keys in both regions.

To troubleshoot and ensure all objects are replicated:

1. Use Amazon S3 replication metrics to monitor the progress and identify any issues.
2. Check the replication status of individual objects in the source bucket.
3. Review your replication configuration and IAM permissions.
4. For objects that existed before setting up replication, consider using S3 Batch Replication to replicate them.
5. If issues persist, you may want to enable Amazon EventBridge for S3 replication events to get detailed notifications about replication failures.

By systematically checking these aspects, you should be able to identify and resolve the cause of the incomplete replication.
Sources
Set up cross-account, cross-Region, encrypted replication for an Amazon S3 bucket | AWS re:Post
Setting up replication - Amazon S3 on Outposts
Managing your replication - Amazon S3 on Outposts
Replicating existing objects with Batch Replication - Amazon Simple Storage Service