Except DocDB is not a drop-in replacement despite what Amazon says.
People have tried and failed to get our software running on DocumentDB, whereas another developer got it running on CosmosDB with minimal changes upstream.
Not affiliated with MS in any way, just sharing what I've witnessed secondhand.
Amazon do not say that DocumentDB is a drop-in replacement, neither do I. Moreover, I have outlined specific incompatibilites between Mongo and DocumentDB we have encountered for our use cases; RBAC controlled document filtering is not available in DocumentDB, either. Therefore, it won't suit everybody.
However, for simple to medium complexity projects, especially for brand new ones, DocumentDB is a viable and a more affordable alternative to Atlas MongoDB with a decent level compatibility.
People have tried and failed to get our software running on DocumentDB, whereas another developer got it running on CosmosDB with minimal changes upstream.
Not affiliated with MS in any way, just sharing what I've witnessed secondhand.