Add Member to MongoDB Replica Set, from the member's side

Question

Let's suppose i have a Replica Set (Master and a bunch of slaves)! I want to automate the fact that a new mongodb node can be selfRegistered to the ReplicaSet without knowing who is the master, and without connecting to it.

Is it possible to add a new member to a MongoDB Replica Set without executing the rs.add() shell command (from the primary node's side) ?

Is it possible for the member to register itself to the Replica Set using some special parameters ? maybe some kind of authentication !

Answer 1

Is it possible to add a new member to a MongoDB Replica Set without executing the rs.add() shell command (from the primary node's side) ?

It is possible, you can execute rs.reconfig() with force option from a secondary member. Although note that using rs.reconfig() with { force: true } can lead to rollback of committed writes. Consider also a case where due to network partition you're connecting to a member that couldn't see to the majority of the replica set members.

A safer way would be to connect to any replica set member, determine the primary member via rs.status() and execute rs.add() via the primary of replica set.

See also database command isMaster()

Is it possible for the member to register itself to the Replica Set using some special parameters ?

As of MongoDB v3.4.x, this is currently not possible. For various reasons, ensuring only the primary member that could alter the Replica Set Configuration for consistency between members is important.