Convert a Standalone mongod to a Replica Set
A standalone mongod
instance is useful for testing and
development. A standalone instance isn't a good choice for a production
deployment because it can be a single point of failure. A replica
set, also known as a cluster, provides redundancy and
availability. Always use a replica set in production.
If you have a standalone server with data that you want to use in production, convert the standalone server to a replica set first.
Important
If you convert a development server to a replica set for production use, consult the security checklist before you expose your cluster to the internet.
You can easily migrate from a standalone server to a MongoDB Atlas cluster. MongoDB Atlas is the fully managed service for MongoDB deployments in the cloud. To learn more, see Migrate or Import Data in the MongoDB Atlas documentation.
Before You Begin
Before you convert your standalone instance, consider whether a replica set or a sharded cluster is more appropriate for your workload.
A sharded cluster is a special kind of cluster. A sharded cluster provides redundancy and availability; it also distributes data across shards. Shards are usually hosted on multiple servers and allow for horizontal scaling.
Procedure
Name the replica set.
If you configure your mongod
instance from the command line,
use the --replSet
option to set a
name for your replica set.
A typical command line invocation might include:
Purpose | Option |
---|---|
Cluster name | |
Network details | |
Data path | |
Authentication details |
Update the example code with the settings for your deployment.
mongod --replSet rs0 \ --port 27017 \ --dbpath /path/to/your/mongodb/dataDirectory \ --authenticationDatabase "admin" \ --username "adminUserName" \ --password
If you use a configuration file to start mongodb
, add a
replication
section to your configuration file. Edit the
replSetName
value to set the name of your replica set.
replication: replSetName: rs0
Note
Optional
You can specify the data directory, replica set name, and the IP
binding in the mongod.conf
configuration file, and start the
mongod
with the following command:
mongod --config /etc/mongod.conf
Initialize the replica set.
To initialize the replica set, use mongosh
to reconnect to
your server instance. Then, run rs.initiate()
.
rs.initiate()
You only have to initiate the replica set once.
To view the replica set configuration, use rs.conf()
.
To check the status of the replica set, use rs.status()
.
Add nodes to the replica set.
The new replica set has a single, primary node. The next step is to add new nodes to the replica set. Review the documentation on clusters before you add additional nodes:
When you are ready to add nodes, use rs.add()
.
Update Your Application Connection String.
After you convert the mongod to a replica set, update the connection string used by your applications to the connection string for your replica set. Then, restart your applications.