Replication

Command summary:

• rs.initiate( { _id: "<replicaSetName>", members: [ { _id: N, host: "<host>" } ] )
• rs.add( "<hostname>" | { host: "<hostname>" } )
• rs.remove( "<hostname>")
• rs.conf()
• rs.status()

The purpose of replication is to provide immediate online redundancy so that there is no loss of service in case of failure. Before we get into the mechanics of how to create and use replicas, it's important to gain an understanding of what MongoDB replication is and how it operates.

Here are a couple of related topics which are beyond the scope of this book, but which might be of interest:
Change streams (https://docs.mongodb.com/manual/changeStreams/#change-streams) allows applications to subscribe to real-time changes in the data by using a Publish-Subscribe design.
Arbiters (https://docs...