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Connection

Connection Guide

On this page

  • Connection URI
  • Atlas Connection Example
  • Other Ways to Connect to MongoDB
  • Connect to a MongoDB Server on Your Local Machine
  • Connect to a Replica Set
  • Direct Connection

This guide shows you how to connect to a MongoDB Atlas deployment, a MongoDB instance, or a replica set using the Node.js driver.

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:

Each part of the connection string

In this example, we connect to an Atlas MongoDB deployment that has a DNS SRV record. For more details, see the DNS Seed List Connection Format documentation. This format offers flexibility in deployment and the ability to change the servers in rotation without reconfiguring clients.

Note

To learn how to retrieve your connection string in Atlas, see the Atlas driver connection guide.

If you are connecting to an instance or replica set that does not have a DNS SRV address, you must use mongodb for the protocol, which specifies the Standard Connection String Format.

After the protocol, the next part of the connection string contains credentials 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 of your MongoDB instance, followed by the port number. In the example above, we use sample.host 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: maxPoolSize=20 and w=majority. For more information on connection options, skip to the Connection Options section.

Atlas Connection Example

You must create a client to connect to a MongoDB deployment on Atlas. To create a client, construct an instance of MongoClient, passing in your URI and a MongoClientOptions object.

Tip

Reuse Your Client

As each MongoClient represents a pool of connections to the database, most applications only require a single instance of a MongoClient, even across multiple requests. To learn more about how connection pools work in the driver, see the FAQ page.

Use the serverApi option in your MongoClientOptions object to enable the Stable API feature, which forces the server to run operations with behavior compatible with the specified API version.

The following code shows how you can specify the connection string and the Stable API client option when connecting to a MongoDB deployment on Atlas and verify that the connection is successful:

const { MongoClient, ServerApiVersion } = require("mongodb");
// Replace the placeholder with your Atlas connection string
const uri = "<connection string>";
// Create a MongoClient with a MongoClientOptions object to set the Stable API version
const client = new MongoClient(uri,  {
        serverApi: {
            version: ServerApiVersion.v1,
            strict: true,
            deprecationErrors: true,
        }
    }
);
async function run() {
  try {
    // Connect the client to the server (optional starting in v4.7)
    await client.connect();
    // Send a ping to confirm a successful connection
    await client.db("admin").command({ ping: 1 });
    console.log("Pinged your deployment. You successfully connected to MongoDB!");
  } finally {
    // Ensures that the client will close when you finish/error
    await client.close();
  }
}
run().catch(console.dir);

To learn more about the Stable API feature, see the Stable API page.

Other Ways to Connect to MongoDB

If you are connecting to a single MongoDB server instance or replica set that is not hosted on Atlas, see the following sections to find out how to connect.

Connect to a MongoDB Server on Your Local Machine

If you need to run a MongoDB server on your local machine for development purposes instead of using an Atlas cluster, you need to complete the following:

  1. Download the Community or Enterprise version of MongoDB Server.

  2. Install and configure MongoDB Server.

  3. Start the server.

Important

Always secure your MongoDB server from malicious attacks. See our Security Checklist for a list of security recommendations.

After you successfully start your MongoDB server, specify your connection string in your driver connection code.

If your MongoDB Server is running locally, you can use the following connection string:

mongodb://localhost:<port>

In this connection string, <port> is the port number on which you configured your server to listen for incoming connections.

If you need to specify a different hostname or IP address, see our Server Manual entry on Connection Strings.

To test whether you can connect to your server, replace the connection string in the Connect to MongoDB code example and run it.

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.

Tip

Specify all hosts

To ensure connectivity if one host is unavailable, provide the full list of hosts when connecting to a replica set.

Direct Connection

To force your operations to run on the host specified in your connection URI, you can specify the directConnection connection option. If you specify this option, you must use the standard connection URI format. The driver does not accept the DNS seedlist connection format (SRV) when you specify this option.

When you specify directConnection and connect to a secondary member of the replica set, your write operations fail because the client isn't connected to the primary member. To perform read operations, you must enable secondary reads. See the read preference options for more information.

← Connection
Connection Options →

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