Fundamentals

Connection Guide¶

This guide shows you how to connect to a MongoDB instance or replica set deployment 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:

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.

Note

If your deployment is on MongoDB Atlas, follow the Atlas driver connection guide to retrieve your connection string.

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

Note

Although it is possible to connect to a replica set deployment by providing only a single host, you should provide the driver with the full list to ensure that it is able to connect even if one host fails.

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.

Option Name	Type	Default Value	Description
connectTimeoutMS	integer	`10000`	Specifies the number of milliseconds to wait before timeout on a TCP connection.
family	number	`null`	Specifies the version of the Internet Protocol (IP). The valid values are: `4`, `6`, `0`, or `null`. The `0` and `null` settings attempt to connect with IPv6 and fall back to IPv4 upon failure.
forceServerObjectId	boolean	`false`	Specifies whether to force the server to assign `_id` values to documents instead of the driver.
ignoreUndefined	boolean	`false`	Specifies whether the BSON serializer should ignore undefined fields.
keepAlive	boolean	`true`	Specifies whether to enable `keepAlive` on the TCP socket. For more information, see the documentation for Node.js socket.setKeepAlive.
keepAliveInitialDelay	integer	`30000`	Specifies the number of milliseconds to wait before initiating `keepAlive` on the TCP socket. For more information, see the documentation for Node.js socket.setKeepAlive.
logger	object	`null`	Specifies a custom logger for the client to use.
loggerLevel	string	`null`	Specifies the logger level used by the driver. Valid choices are: `error`, `warn`, `info`, and `debug`.
minSize	integer	`0`	Specifies the minimum size of the instance connection pool.
noDelay	boolean	`true`	Specifies whether to use the TCP socket no-delay option. For more information, see the documentation for Node.js socket.setNoDelay.
pkFactory	object	`null`	Specifies a primary key factory object that generates custom `_id` keys.
poolSize	integer	`5`	Specifies the maximum size of the instance connection pool.
promiseLibrary	object	`null`	Specifies the Promise library class the application uses (e.g. Bluebird). This library must be compatible with ES6.
promoteBuffers	boolean	`false`	Specifies whether to promote Binary BSON values to native Node.js `Buffer` type data.
promoteLongs	boolean	`true`	Specifies whether to convert `Long` values to a number if they fit inside 53 bits of resolution.
promoteValues	boolean	`true`	Specifies whether to promote BSON values to Node.js native types when possible. When set to false, it uses wrapper types to present BSON values.
raw	boolean	`false`	Specifies whether to return document results as raw BSON buffers.
serializeFunctions	boolean	`false`	Specifies whether to serialize functions on any object passed to the server.
socketTimeoutMS	integer	`360000`	Specifies the number of milliseconds to wait before timeout on a TCP socket.
tls	boolean	`false`	Specifies whether to establish a Transport Layer Security (TLS) connection with the instance. This is automatically set to `true` when using a DNS seedlist (SRV) in the connection string. You can override this behavor by setting the value to `false`.
validateOptions	boolean	`false`	Specifies whether to error when the method parameters contain an unknown or incorrect option. If `false`, the driver produces warnings only.
writeConcern	string or integer	`null`	Specifies the write concern. For more information on values, see the server documentation on the w Option.

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

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