https://techcrunch.com/2019/01/09/aws-gives-open-source-the-middle-finger/

AWS launched DocumentDB today, a new database offering that is compatible with the MongoDB API. The company describes DocumentDB as a “fast, scalable, and highly available document database that is designed to be compatible with your existing MongoDB applications and tools.” In effect, it’s a hosted drop-in replacement for MongoDB that doesn’t use any MongoDB code.

AWS argues that while MongoDB is great at what it does, its customers have found it hard to build fast and highly available applications on the open-source platform that can scale to multiple terabytes and hundreds of thousands of reads and writes per second. So what the company did was build its own document database, but made it compatible with the Apache 2.0 open source MongoDB 3.6 API.