title: MongoDB one way replication
body: <p>Need some way to push data from clients database to central database.Basically, there are several instances of MongoDB running on remote machines [clients] , and need some method to periodically update central mongo database with newly added and modified documents in clients.it must replicate its records to the single central server</p>
  
  <p>Eg:</p>
  
  <p>If I have 3 mongo instances running on 3 machines each having data of 10GB then after the data migration 4th machine's mongoDB must have 30GB of data.  And  cenral mongoDB machine must get periodically updated with data of all those 3 machines. But these 3 machines not only get new documents but existing documents in them may get updated. I would like the central mongoDB machine also to get these updations.</p>