I've seen a couple of successful ones, but there were extremely good reasons: Most of the time we don't need scaling, but when your target Mongo cluster has a c

I've seen a couple of successful ones, but there were extremely good reasons: Most of the time we don't need scaling, but when your target Mongo cluster has a couple hundred machines, and your queries really are very simple, NoSQL is not a crazy idea. Same with DynamoDB: Sometimes it really is a very good choice, but you need a use case of the right shape. If you have an extremely good use case for your table to be in 5+ regions, the dataset has billions of rows and you have no hot keys, maybe running your own replication system really is more effort than letting AWS do it all for you. It's just far more common for some tech lead in small company to imagine that they are going to be bigger than Netflix, than for someone to start conservatively with a RDBMS, and realize that suddenly they have hundreds of millions of users and some kinds of data where the relational bits don't matter.