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Change Hostnames in a 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.
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.
Open a
mongo
shell connected to the replica set’s primary. In our example, the primary runs on port27017
so you would issue the following command:mongo --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.
Open a
mongo
shell connected 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)
Open a
mongo
shell connected to the new primary.To confirm the new configuration, call
rs.conf()
in themongo
shell.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 Auth.mongo --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. At minimum, consider enabling authentication and hardening network infrastructure.
mongod --dbpath /data/db1/ --port 37017 --bind_ip localhost,<ip address of the mongod host>
For each member of the replica set, perform the following sequence of operations: