Deploy a Replica Set

Open the Create New Database Deployment dialog box

1. In the MongoDB Atlas UI, click Database in the sidebar.

2. If you already have one or more database deployments, click Create. If this is your first database deployment, click Build a Database, then click Advanced Configuration Options.

Select cluster options

1. Click Shared.

2. Select a cloud provider and region. To learn more, see Cloud Providers and Regions.

3. Expand the Cluster Details section and specify a name for the cluster in the Cluster Name field.

Click Create Cluster

MongoDB Atlas deploys a free, three-node replica set with the cluster name you specified.

Start each member of the replica set with the appropriate options.

For each member, start a mongod instance with the following settings:

• Set replication.replSetName option to the replica set name. If your application connects to more than one replica set, each set must have a distinct name.

• Set net.bindIp option to the hostname/ip or a comma-delimited list of hostnames/ips.

• Set any other settings as appropriate for your deployment.

In this tutorial, the three mongod instances are associated with the following hosts:

The following example specifies the replica set name and the ip binding through the --replSet and --bind_ip command-line options:

mongod --replSet "rs0" --bind_ip localhost,<hostname(s)|ip address(es)>

For <hostname(s)|ip address(es)>, specify the hostname(s) and/or ip address(es) for your mongod instance that remote clients (including the other members of the replica set) can use to connect to the instance.

Alternatively, you can also specify the replica set name and the ip addresses in a configuration file:

replication:
   replSetName: "rs0"
net:
   bindIp: localhost,<hostname(s)|ip address(es)>

To start mongod with a configuration file, specify the configuration file's path with the --config option:

mongod --config <path-to-config>

In production deployments, you can configure a init script to manage this process. Init scripts are beyond the scope of this document.

Connect mongosh to one of the mongod instances.

From the same machine where one of the mongod is running (in this tutorial, mongodb0.example.net), start mongosh. To connect to the mongod listening to localhost on the default port of 27017, simply issue:

mongosh

Depending on your path, you may need to specify the path to the mongosh binary.

If your mongod is not running on the default port, specify the --port option for mongosh.

Initiate the replica set.

From mongosh, run rs.initiate() on replica set member 0.

rs.initiate( {
   _id : "rs0",
   members: [
      { _id: 0, host: "mongodb0.example.net:27017" },
      { _id: 1, host: "mongodb1.example.net:27017" },
      { _id: 2, host: "mongodb2.example.net:27017" }
   ]
})

MongoDB initiates a replica set, using the default replica set configuration.

View the replica set configuration.

Use rs.conf() to display the replica set configuration object:

rs.conf()

The replica set configuration object resembles the following:

{
   "_id" : "rs0",
   "version" : 1,
   "protocolVersion" : NumberLong(1),
   "members" : [
      {
         "_id" : 0,
         "host" : "mongodb0.example.net:27017",
         "arbiterOnly" : false,
         "buildIndexes" : true,
         "hidden" : false,
         "priority" : 1,
         "tags" : {
         },
         "secondaryDelaySecs" : NumberLong(0),
         "votes" : 1
      },
      {
         "_id" : 1,
         "host" : "mongodb1.example.net:27017",
         "arbiterOnly" : false,
         "buildIndexes" : true,
         "hidden" : false,
         "priority" : 1,
         "tags" : {
         },
         "secondaryDelaySecs" : NumberLong(0),
         "votes" : 1
      },
      {
         "_id" : 2,
         "host" : "mongodb2.example.net:27017",
         "arbiterOnly" : false,
         "buildIndexes" : true,
         "hidden" : false,
         "priority" : 1,
         "tags" : {
         },
         "secondaryDelaySecs" : NumberLong(0),
         "votes" : 1
      }
      
   ],
   "settings" : {
      "chainingAllowed" : true,
      "heartbeatIntervalMillis" : 2000,
      "heartbeatTimeoutSecs" : 10,
      "electionTimeoutMillis" : 10000,
      "catchUpTimeoutMillis" : -1,
      "getLastErrorModes" : {
      },
      "getLastErrorDefaults" : {
         "w" : 1,
         "wtimeout" : 0
      },
      "replicaSetId" : ObjectId("585ab9df685f726db2c6a840")
   }
}

Ensure that the replica set has a primary.

Use rs.status() to identify the primary in the replica set.