I am running a (keystonejs) webapp using mongodb 3.0 as database. I cloned the webapp and run a second instance using a 3.2 mongodb release (on a generated but yet empty data base). What I need to do now is get the data from the first database to the second. Since mongodb 3.2 uses a different default storage engine which is WiredTiger the clone uses that one. However the original app uses MMAPv1. Is there a easy way to migrate data create by MMAPv1 to WiredTiger?
Create a backup of the database on your old server using mongodump, restore it back to the new one using mongorestore, done. It's covered quite well in the documentation.
https://docs.mongodb.org/manual/tutorial/change-standalone-wiredtiger/