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Convert a Standalone to a Replica Set

This tutorial describes the process for converting a standalone mongod instance into a replica set. Use standalone instances for testing and development, but always use replica sets in production.

The procedure is specific to instances that are not part of a sharded cluster. To convert a shard standalone instance to a shard replica set, see Convert a Shard Standalone to a Shard Replica Set instead.

To deploy a replica set without using a pre-existing mongod instance, see Deploy a Replica Set instead.

To install a standalone instance, see the installation tutorials.


  1. Shut down the standalone mongod instance.

  2. Restart the instance. Use the --replSet option to specify the name of the new replica set.

    For example, the following command starts a standalone instance as a member of a new replica set named rs0. The command uses the standalone’s existing database path of /srv/mongodb/db0:


    Before binding to a non-localhost (e.g. publicly accessible) IP address, ensure you have secured your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.

    mongod --port 27017 --dbpath /srv/mongodb/db0 --replSet rs0 --bind_ip localhost,<ip address of the mongod host>

    If your application connects to more than one replica set, each set should have a distinct name. Some drivers group replica set connections by replica set name.

    For more information on configuration options, see Configuration File Options and the mongod manual page.

  3. Connect a mongo shell to the mongod instance.

  4. Use rs.initiate() to initiate the new replica set:


    The replica set is now operational. To view the replica set configuration, use rs.conf(). To check the status of the replica set, use rs.status().

To add members to this replica set, use the rs.add() method. For more information on adding members to a replica set, see Add Members to a Replica Set.