We can change the configuration of the replica set as per the requirement of the application. Configuration changes may include ADDING a new member, adding Arbiter, removing a member, changing priority or votes for members, or changing member from normal secondary to hidden or delayed member.

To ADD a new member, first we NEED to start the mongod process –replset option on the new server

• To add new secondary

rs.add({host: “hostname” , port : “portno.”})

Once added member will FETCH the data from primary using initial sync and replication synchronism.

• To add Arbiter 

rs.addArb({host: “hostname” , port : “portno.”})

• To remove a member

rs.remove(hostname)

As a good practice should shut down the member being removed before running the above command.

1. Above steps can also be performed using below command providing new configuration.

rs.reconfig(new config)

Reconfig can be explained better with below example. Suppose we have replica set “rs0” with below configuration.

• To change the priority of member 1:

From Primary:

• To change the Votes of member 2:

• To change current secondary member as a delayed member with 1-hour delay.

• To change current secondary member to hidden member