Connection Guide¶

Connection URI¶

The connection URI is the set of instructions that the driver uses to connect to a MongoDB deployment. It instructs the driver on how it should connect to MongoDB and how it should behave while connected. The following example shows each part of the connection URI:

In this example, for the protocol, we use mongodb+srv which specifies the DNS Seedlist Connection Format. This indicates that the hostname following it corresponds to the DNS SRV record of your MongoDB instance or deployment. If your instance or deployment does not have a DNS SRV record, use mongodb to specify the Standard Connection Format.

The next part of the connection string contains your username and password if you are using password-based authentication. Replace the value of user with your username and pass with your password. If you are using an authentication mechanism that does not require a username and password, omit this part of the connection URI.

The next part of the connection string specifies the hostname or IP address and port of your MongoDB instance. In the example above, we use sample-hostname as the hostname and 27017 as the port. Replace these values to point to your MongoDB instance.

The last part of the connection string contains connection and authentication options as parameters. In the example above, we set two connection options: poolSize=20 and writeConcern=majority. For more information on connection options, skip to the Connection Options section.

The code below shows how you can use the sample connection URI in a client to connect to MongoDB.

const { MongoClient } = require("mongodb");
// Connection URI
const uri =
  "mongodb+srv://sample-hostname:27017/?poolSize=20&writeConcern=majority";
// Create a new MongoClient
const client = new MongoClient(uri);
async function run() {
  try {
    // Connect the client to the server
    await client.connect();
    // Establish and verify connection
    await client.db("admin").command({ ping: 1 });
    console.log("Connected successfully to server");
  } finally {
    // Ensures that the client will close when you finish/error
    await client.close();
  }
}
run().catch(console.dir);

Connect to a Replica Set¶

A MongoDB replica set deployment is a group of connected instances that store the same set of data. This configuration of instances provides data redundancy and high data availability.

To connect to a replica set deployment, specify the hostname and port numbers of each instance, separated by a comma, and the replica set name as the value of the replicaSet parameter in the connection string.

mongodb://host1:27017,host2:27017,host3:27017/?replicaSet=myRs

When making a connection, the driver takes the following actions by default:

• Discovers all replica set members when given the address of any one member.
• Dispatches operations to the appropriate member, such as write against the primary.

Connection Options¶

This section explains several common MongoDB connection and authentication options. You can pass the connection options as parameters of the connection URI to specify the behavior of the client.

For a complete list of options, see the MongoClient API reference page.