For dynamodb it was “you need to rethink your data structure”
S3, I think they did up the bucket limit on request, but maxed out at 1,000. That was years ago though.
I guess the way they want you to do it in S3 is using a per tenant key prefix with security policy set? AWS roles and security policies are quite flexible so I guess in theory you would get the desired isolation that way. Separate buckets are still easier, though...
Did Amazon mere said, "you are doing it wrong", without an explanation? In retrospective, do you think you could have done better? I'm looking to hear the lessons you learned, so may be, I don't end up making that mistake ;)