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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.

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.



When possible, use a logical DNS hostname instead of an ip address, particularly when configuring replica set members or sharded cluster members. The use of logical DNS hostnames avoids configuration changes due to ip address changes.

  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,<hostname(s)|ip address(es)>

    If your application connects to more than one replica set, each set must 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.