Data Federation Limitations
Data Federation does not support the following features:
Authenticating with methods other than SCRAM or X.509 Certificates
Monitoring federated database instances with Atlas monitoring tools
Creating a federated database instance with S3 buckets from more than one AWS account
Querying documents larger than 16MB
Returning documents in the same order across queries unless imposed by the query operators used
Having more than 60 guaranteed simultaneous connections per region to a federated database instance
Running more than 30 simultaneous queries on your federated database instance
If your aggregation pipeline only contains the $currentOp stage, Atlas Data Federation doesn't enforce the limit on the maximum number of simultaneous queries. You can run queries that only contain the $currentOp stage even after you reach the maximum number of simultaneous queries.
Atlas Data Federation automatically expires your cursor if you do not consume at least 16MiB of results every 1 minute.