rs.initiate()¶

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Description
IP Binding
Replica Set Configuration
Example

Description¶

rs.initiate(configuration)¶

Initiates a replica set. Optionally, the method can take an argument in the form of a document that holds the configuration of a replica set.

The rs.initiate() method has the following parameter:

Parameter	Type	Description
`configuration`	document	Optional. A document that specifies configuration for the new replica set. If a configuration is not specified, MongoDB uses a default replica set configuration.

The rs.initiate() method provides a wrapper around the replSetInitiate command.

IP Binding¶

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.

MongoDB binaries, mongod and mongos, bind to localhost by default. If the net.ipv6 configuration file setting or the --ipv6 command line option is set for the binary, the binary additionally binds to the localhost IPv6 address.

By default mongod and mongos that are bound to localhost only accept connections from clients that are running on the same computer. This binding behavior includes mongosh and other members of your replica set or sharded cluster. Remote clients cannot connect to binaries that are bound only to localhost.

To override the default binding and bind to other IP addresses, use the net.bindIp configuration file setting or the --bind_ip command-line option to specify a list of hostnames or IP addresses.

Warning

Starting in MongDB 5.0, split horizon DNS nodes that are only configured with an IP address fail startup validation and report an error. See disableSplitHorizonIPCheck.

For example, the following mongod instance binds to both the localhost and the hostname My-Example-Associated-Hostname, which is associated with the IP address 198.51.100.1:

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mongod --bind_ip localhost,My-Example-Associated-Hostname

In order to connect to this instance, remote clients must specify the hostname or its associated IP address 198.51.100.1:

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mongosh --host My-Example-Associated-Hostname

mongosh --host 198.51.100.1

Replica Set Configuration¶

See Replica Set Configuration Document Example for details of the replica set configuration document.

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 MongDB 5.0, nodes that are only configured with an IP address will fail startup validation and will not start.

Example¶

The following example initiates a new replica set with three members.

The three mongod instances must have started with the --replSet command line option (or replication.replSetName if using a configuration file) set to myReplSet and the --bind_ip (or net.bindIp if using a configuration file) set appropriately such that other members of the replica set and clients can connect.

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.

Connect mongosh to one of the mongod instances and run rs.initiate().

Note

Run rs.initiate() on just one and only one mongod instance for the replica set.

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 MongDB 5.0, nodes that are only configured with an IP address will fail startup validation and will not start.

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

For details on replica set configuration, see Replica Set Configuration Fields.

For details on deploying a replica set, see Deploy a Replica Set.