AMAZON S3 NOW SUPPORTS CONDITIONAL WRITES

Summary from the TLDR newsletter

Amazon S3 now supports conditional writes that can check for the existence of an object before creating it. This helps developers more easily prevent applications from overwriting any existing objects when uploading data. Conditional writes can be used to simplify how distributed applications with multiple clients concurrently update data in parallel across shared datasets. Developers no longer need to build any client-side consensus mechanisms to coordinate updates or use additional API requests to check for the presence of an object before uploading data. The feature is available at no additional charge in all AWS regions.