Change Hostnames in a Self-Managed Replica Set
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For most replica sets, the hostnames in the
members[n].host
field never change.
However, if organizational needs change, you might need to migrate some
or all host names.
Note
Always use resolvable hostnames for the value of the
members[n].host
field in the replica
set configuration to avoid confusion and complexity.
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 fail startup validation and do not start.
Overview
This document provides two separate procedures for changing the
hostnames in the members[n].host
field. Use either of the following approaches:
Change hostnames without disrupting availability. This approach ensures your applications will always be able to read and write data to the replica set, but the approach can take a long time and may incur downtime at the application layer.
If you use the first procedure, you must configure your applications to connect to the replica set at both the old and new locations, which often requires a restart and reconfiguration at the application layer and which may affect the availability of your applications. Re-configuring applications is beyond the scope of this document.
Stop all members running on the old hostnames at once. This approach has a shorter maintenance window, but the replica set will be unavailable during the operation.
Assumptions
Given a replica set with three members:
database0.example.com:27017
(the primary)database1.example.com:27017
database2.example.com:27017
And with the following rs.conf()
output:
{ "_id" : "rs", "version" : 3, "members" : [ { "_id" : 0, "host" : "database0.example.com:27017" }, { "_id" : 1, "host" : "database1.example.com:27017" }, { "_id" : 2, "host" : "database2.example.com:27017" } ] }
The following procedures change the members' hostnames as follows:
mongodb0.example.net:27017
(the primary)mongodb1.example.net:27017
mongodb2.example.net:27017
Use the most appropriate procedure for your deployment.
Change Hostnames while Maintaining Replica Set Availability
This procedure uses the above assumptions.
For each secondary in the replica set, perform the following sequence of operations:
Stop the secondary.
Restart the secondary at the new location.
Connect
mongosh
to the replica set's primary. In our example, the primary runs on port27017
so you would issue the following command:mongosh --port 27017 Use
rs.reconfig()
to update the replica set configuration document with the new hostname.For example, the following sequence of commands updates the hostname for the secondary at the array index
1
of themembers
array (i.e.members[1]
) in the replica set configuration document:cfg = rs.conf() cfg.members[1].host = "mongodb1.example.net:27017" rs.reconfig(cfg) For more information on updating the configuration document, see Examples.
Make sure your client applications are able to access the set at the new location and that the secondary has a chance to catch up with the other members of the set.
Repeat the above steps for each non-primary member of the set.
Connect
mongosh
to the primary and step down the primary using thers.stepDown()
method:rs.stepDown() The replica set elects another member to the become primary.
When the step down succeeds, shut down the old primary.
Start the
mongod
instance that will become the new primary in the new location.Connect to the current primary, which was just elected, and update the replica set configuration document with the hostname of the node that is to become the new primary.
For example, if the old primary was at position
0
and the new primary's hostname ismongodb0.example.net:27017
, you would run:cfg = rs.conf() cfg.members[0].host = "mongodb0.example.net:27017" rs.reconfig(cfg) Connect
mongosh
to the new primary.To confirm the new configuration, call
rs.conf()
inmongosh
.Your output should resemble:
{ "_id" : "rs", "version" : 4, "members" : [ { "_id" : 0, "host" : "mongodb0.example.net:27017" }, { "_id" : 1, "host" : "mongodb1.example.net:27017" }, { "_id" : 2, "host" : "mongodb2.example.net:27017" } ] }
Change All Hostnames at the Same Time
This procedure uses the above assumptions.
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:
Log in as a user with privileges to manage users and roles, such as a user with
userAdminAnyDatabase
role. The following procedure uses themyUserAdmin
created in Enable Access Control on Self-Managed Deployments.mongosh --port 27017 -u myUserAdmin --authenticationDatabase 'admin' -p Create a user role that provides the necessary privileges on the
system.replset
collection in thelocal
database:db.adminCommand( { createRole: "systemreplsetRole", privileges: [ { resource: { db: "local", collection: "system.replset" }, actions: ["find","update"] } ], roles: [] } ); Grant the role to the user who will be performing the rename procedure. For example, the following assumes an existing user
"userPerformingRename"
in theadmin
database.use admin db.grantRolesToUser( "userPerformingRename", [ { role: "systemreplsetRole", db: "admin" } ] );
Procedure
Stop all members in the replica set.
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 for Self-Managed Deployments. 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 fail startup validation and do not start.
For each member of the replica set, perform the following sequence of operations:
Connect
mongosh
to themongod
running on the new, temporary port. For example, for a member running on a temporary port of37017
, 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 Edit the replica set configuration manually. The replica set configuration is the only document in the
system.replset
collection in thelocal
database.To change the hostnames, edit the replica set configuration to provide the new hostnames and ports for all members of the replica set.
Switch to the
local
database.use local 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" } ) 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" Update the hostnames and ports in the
system.replset
collection:db.system.replset.updateOne( { "_id": "rs0" }, { $set: cfg } ) Verify the changes:
db.system.replset.find( {}, { "members.host": 1 } )
Stop the
mongod
process on the member.
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 for Self-Managed Deployments. 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)> Connect to one of the
mongod
instances usingmongosh
. For example:mongosh --port 27017 To confirm the new configuration, call
rs.conf()
inmongosh
.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" } ] }