Cloud objects, versions and integrity
Object storage addresses data by a bucket and key. A slash in a key often creates a folder-like interface; it need not be a filesystem directory.
Preserve useful metadata
Choose a stable key and an appropriate Content-Type. Record the object version where versioning is available, rather than relying only on a mutable key.
Check the checksum field
Do not assume an Amazon S3 ETag is the MD5 of the complete file. Multipart uploads and some encryption modes break that assumption. Use a documented checksum field and understand whether it covers the entire object or is composite.
Keep the source file until upload completion and verification. Remove abandoned multipart uploads through an appropriate lifecycle rule.
References: S3 object metadata and multipart uploads.