How do I rename a mongodb replica set?

Yes! The process is pretty simple:

1. Start all of the nodes in the non-replicated mode
   • Stop mongod on each server
   • Start mongod back up. If you use /etc/mongod.conf, remove the replication section. If you don't, omit the --replSet option to mongod

2. Flush the local database where the replication set configuration is cached

   • On each server, open a mongo shell as the admin user and run use local; db.dropDatabase() (Make sure that admin user / root user has dbAdmin role on local db)

3. Start all of the nodes again in replicated mode

   • Stop mongod on each server
   • If you use /etc/mongod.conf, add the replication section back in with the new name and start mongod. If not, start mongod with --replSet <new-name>
4. Initialize the replica set
   • Open a mongo shell as the admin user on one of the nodes. (It will become the new primary)
   • Run rs.initiate(). DO NOT pass any arguments to rs.initiate(). (It'll fail with an error) Any other config you want to set can be changed using rs.reconfig() later.
   • On the same node where your ran rs.initiate(), for each secondary, run rs.add('[secondary.host.name]') to add it to the replica set.
   • Wait for the secondaries to come in sync

This doesn't require you to dump and re-import your data, and it can be done with minimal downtime (and a period of degraded performance as the secondaries sync) if you automate it.

Here's an ansible playbook that does the whole thing (assuming you're using /etc/mongod.conf and managing mongod via System V/Upstart/things that speak service.)