AWS Database Migration Service now supports MongoDB 4.0 as a source
AWS Database Migration Service (AWS DMS) has expanded functionality by adding support for MongoDB 4.0 as a source in AWS DMS v 3.4.1. Using DMS, you can now perform live migrations from MongoDB 4.0 clusters to any AWS DMS supported target including Amazon DocumentDB (with MongoDB compatibility) with minimal downtime. For full list of supported AWS DMS targets, see targets for data migration.
Source:: Amazon AWS