Amazon S3 now supports enforcement of conditional write operations for S3 general purpose buckets
Amazon S3 now supports enforcement of conditional write operations for S3 general purpose buckets using bucket policies. With enforcement of conditional writes, you can now mandate that S3 check the existence of an object before creating it in your bucket. Similarly, you can also mandate that S3 check the state of the object’s content before updating it in your bucket. This helps you to simplify distributed applications by preventing unintentional data overwrites, especially in high-concurrency, multi-writer scenarios.
To enforce conditional write operations, you can now use s3:if-none-match or s3:if-match condition keys to write a bucket policy that mandates the use of HTTP if-none-match or HTTP if-match conditional headers in S3 PutObject and CompleteMultipartUpload API requests. With this bucket policy in place, any attempt to write an object to your bucket without the required conditional header will be rejected. You can use this to centrally enforce the use of conditional writes across all the applications that write to your bucket.
You can use bucket policies to enforce conditional writes at no additional charge in all AWS Regions. You can use the AWS SDK, API, or CLI to perform conditional writes. To learn more about conditional writes, visit the S3 User Guide.