Change Hostnames in a Replica Set

Prerequisites

The following procedure reads and updates the system.replset collection in the local database.

If your deployment enforces access control, the user performing the procedure must have find and update privilege actions on the system.replset collection.

To create a role that provides the necessary privileges:

1. Log in as a user with privileges to manage users and roles, such as a user with userAdminAnyDatabase role. The following procedure uses the myUserAdmin created in Enable Access Control.

   mongosh --port 27017 -u myUserAdmin --authenticationDatabase 'admin' -p

2. Create a user role that provides the necessary privileges on the system.replset collection in the local database:

   db.adminCommand( {
      createRole: "systemreplsetRole",
      privileges: [
         { resource: { db: "local", collection: "system.replset" }, actions: ["find","update"] }
      ],
      roles: []
   } );

3. Grant the role to the user who will be performing the rename procedure. For example, the following assumes an existing user "userPerformingRename" in the admin database.

   use admin
   db.grantRolesToUser( "userPerformingRename", [ { role: "systemreplsetRole", db: "admin" } ] );

Procedure

1. Stop all members in the replica set.

2. Restart each member on a different port and without using the --replSet run-time option. Changing the port number during maintenance prevents clients from connecting to this host while you perform maintenance. Use the member's usual --dbpath, which in this example is /data/db1. Use a command that resembles the following:

   Warning

   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 --dbpath /data/db1/ --port 37017 --bind_ip localhost,<hostname(s)|ip address(es)>

   Important

   To avoid configuration updates due to IP address changes, use DNS hostnames instead of IP addresses. It is particularly important to use a DNS hostname instead of an IP address when configuring replica set members or sharded cluster members.

   Use hostnames instead of IP addresses to configure clusters across a split network horizon. Starting in MongoDB 5.0, nodes that are only configured with an IP address will fail startup validation and will not start.

3. For each member of the replica set, perform the following sequence of operations:

   1. Connect mongosh to the mongod running on the new, temporary port. For example, for a member running on a temporary port of 37017, you would issue this command:

      mongosh --port 37017

      If running with access control, connect as a user with appropriate privileges. See Prerequisites.

      mongosh --port 37017 -u userPerformingRename --authenticationDatabase=admin  -p

   2. Edit the replica set configuration manually. The replica set configuration is the only document in the system.replset collection in the local database.

      
      

      To change the hostnames, edit the replica set configuration to provide the new hostnames and ports for all members of the replica set.

      1. Switch to the local database.

         use local

      2. Create a JavaScript variable for the configuration document. Modify the value of the _id field to match your replica set.

         cfg = db.system.replset.findOne( { "_id": "rs0" } )

      3. Provide new hostnames and ports for each member of the replica set. Modify the hostnames and ports to match your replica set.

         cfg.members[0].host = "mongodb0.example.net:27017"
         cfg.members[1].host = "mongodb1.example.net:27017"
         cfg.members[2].host = "mongodb2.example.net:27017"

      4. Update the hostnames and ports in the system.replset collection:

         db.system.replset.updateOne( { "_id": "rs0" }, { $set: cfg } )

      5. Verify the changes:

         db.system.replset.find( {}, { "members.host": 1 } )

   3. Stop the mongod process on the member.

4. After re-configuring all members of the set, start each mongod instance in the normal way: use the usual port number and use the --replSet option. For example:

   Warning

   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 --dbpath /data/db1/ --port 27017 --replSet rs0 --bind_ip localhost,<hostname(s)|ip address(es)>

5. Connect to one of the mongod instances using mongosh. For example:

   mongosh --port 27017

6. To confirm the new configuration, call rs.conf() in mongosh.

   Your output should resemble:

   {
       "_id" : "rs0",
       "version" : 4,
       "members" : [
           {
               "_id" : 0,
               "host" : "mongodb0.example.net:27017"
           },
           {
               "_id" : 1,
               "host" : "mongodb1.example.net:27017"
           },
           {
               "_id" : 2,
               "host" : "mongodb2.example.net:27017"
           }
       ]
   }