The Live Migration Service is a free service that we host and operate to make it simple to migrate your database to MongoDB Atlas.
This service works by making an initial copy of the data from your source database, and watching for any changes so that it stays in sync until you are ready to cut over.
During this process, your application can continue to read and write from your source database.
When you are ready, change the connection string in your application from your source database to your Atlas cluster, and the migration is complete.