Azure has been running a Mongo-compliant DB under their Cosmos umbrella for quite a while. It's not clear to me that either Azure or AWS are actually running Mongo software under the hood or rather a proprietary DB that uses the Mongo wire protocol.

https://docs.microsoft.com/en-us/azure/cosmos-db/mongodb-int...

Doesn’t Azure also have a not-Mongo service also called DocumentDB? Is this the same code? These cloud services are confusing enough when they don’t borrow each other’s names.

The Azure service formerly known as DocumentDB is now called Cosmos DB. Part of that switch was introducing multiple APIs, including a MongoDB API: https://docs.microsoft.com/en-us/azure/cosmos-db/mongodb-int...

Correct. They added more gateway compat layers in addition to Mongo and renamed it from DocumentDB to Azure CosmosDB then.

That’s now Azure CosmosDB because it offers several different APIs for your data.

it's not mongo software, there are some incompatibilities.

I think it is likely it was the other way around. MongoDB caught wind of what AWS was about to release and changed the license.

Does that even apply? This is api-compatible, but doesn't appear to be using any actual MongoDB code.

It seems like Amazon may think so, with this line:

> Amazon DocumentDB implements the Apache 2.0 open source MongoDB 3.6 API by emulating the responses that a MongoDB client expects from a MongoDB server

Yeah, along with the FDB document layer: https://www.foundationdb.org/blog/announcing-document-layer/