And Dropbox for 8 years of its life was basically this:
aws s3 sync source destination
aws s3 sync source destination
If you need backup, then use rsync, but Dropbox isn't just backup.
aws s3 presign s3://<bucketname>/<object>
The original rsync comment, here in this community, does not get the respect that it deserves. If you are a user, maybe you should read this:
"Criticism of Dropbox" https://en.wikipedia.org/wiki/Criticism_of_Dropbox
"...Half-a-billion people stored files on Dropbox. Well, sort of. Really, the files were in Amazon’s cloud..."
https://www.wired.com/2016/03/epic-story-dropboxs-exodus-ama...