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.

If you’ve been following the politics of open source over the last few months, you’ll understand that the optics of this aren’t great. It’s also no secret that AWS has long been accused of taking the best open-source projects and re-using and re-branding them without always giving back to those communities.

The wrinkle here is that MongoDB was one of the first companies that aimed to put a stop to this by re-licensing its open-source tools under a new license that explicitly stated that companies that wanted to do this had to buy a commercial license. Since then, others have followed.

“Imitation is the sincerest form of flattery, so it’s not surprising that Amazon would try to capitalize on the popularity and momentum of MongoDB’s document model,” MongoDB CEO and president Dev Ittycheria told us. “However, developers are technically savvy enough to distinguish between the real thing and a poor imitation. MongoDB will continue to outperform any impersonations in the market.”

That’s a pretty feisty comment. Last November, Ittycheria told my colleague Ron Miller that he believed that AWS loved MongoDB because it drives a lot of consumption. In that interview, he also noted that “customers have spent the last five years trying to extricate themselves from another large vendor. The last thing they want to do is replay the same movie.”

MongoDB co-founder and CTO Eliot Horowitz echoed this. “In order to give developers what they want, AWS has been pushed to offer an imitation MongoDB service that is based on the MongoDB code from two years ago,” he said. “Our entire company is focused on one thing — giving developers the best way to work with data with the freedom to run anywhere. Our commitment to that single mission will continue to differentiate the real MongoDB from any imitation products that come along.”

A company spokesperson for MongoDB also highlighted that the 3.6 API that DocumentDB is compatible with is now two years old and misses most of the newest features, including ACID transactions, global clusters and mobile sync.

To be fair, AWS has become more active in open source lately and, in a way, it’s giving developers what they want (and not all developers are happy with MongoDB’s own hosted service). Bypassing MongoDB’s licensing by going for API comparability, given that AWS knows exactly why MongoDB did that, was always going to be a controversial move and won’t endear the company to the open-source community.