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mongodb / v3.6 / reference / reference-command-replSetInitiate.html

replSetInitiate

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replSetInitiate

The replSetInitiate command initializes a new replica set.

To run replSetInitiate, use the db.runCommand( { <command> } ) method.

Note

Run the command on only one of the mongod instances for the replica set.

Use the following syntax:

{ replSetInitiate : <config_document> }

The <config_document> is a document that specifies the replica set’s configuration. For instance, here’s a config document for creating a simple 3-member replica set:

{
    _id : <setname>,
     members : [
         {_id : 0, host : <host0>},
         {_id : 1, host : <host1>},
         {_id : 2, host : <host2>},
     ]
}

IP Binding

Starting in MongoDB 3.6, MongoDB binaries, mongod and mongos, bind to localhost (127.0.0.1) 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 IPv6 address ::1.

Previously, starting from MongoDB 2.6, only the binaries from the official MongoDB RPM (Red Hat, CentOS, Fedora Linux, and derivatives) and DEB (Debian, Ubuntu, and derivatives) packages bind to localhost by default.

When bound only to the localhost, these MongoDB 3.6 binaries can only accept connections from clients (including the mongo shell, other members in your deployment for replica sets and sharded clusters) that are running on the same machine. Remote clients cannot connect to the binaries bound only to localhost.

To override and bind to other ip addresses, you can use the net.bindIp configuration file setting or the --bind_ip command-line option to specify a list of ip addresses.

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.

For example, the following mongod instance binds to both the localhost and the sample ip address 198.51.100.1:

mongod --bind_ip localhost,198.51.100.1

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

mongo --host 198.51.100.1

mongo --host My-Example-Associated-Hostname

Example

Assign a config document to a variable and then to pass the document to the rs.initiate() helper:

config = {
    _id : "my_replica_set",
     members : [
         {_id : 0, host : "rs1.example.net:27017"},
         {_id : 1, host : "rs2.example.net:27017"},
         {_id : 2, host : "rs3.example.net", arbiterOnly: true},
     ]
}

rs.initiate(config)

Notice that omitting the port cause the host to use the default port of 27017. Notice also that you can specify other options in the config documents such as the arbiterOnly setting in this example.