Link a MongoDB Data Source

You can use MongoDB Realm to work with a data source -- either a MongoDB Atlas cluster or Data Lake associated with the same Atlas project as your Realm app. To connect to a data source through Realm, you must first link it to a new MongoDB service in your application.

You can create a MongoDB service and link a data source to your Realm app through the Realm UI or with an import/export configuration directory. Select the tab below that corresponds to the method you want to use.

Version 4.4 Required for Sync

In order to use Realm Sync, your Atlas cluster must use MongoDB version 4.4.


In the Realm UI, click Linked Data Sources under Manage in the left navigation menu.


Click Link a Data Source and provide the following configuration information on the Data Source Configuration screen:

Data Source
A MongoDB Atlas cluster or Data Lake associated with the same project as your Realm app.
Realm Service Name

A name for the Realm service that connects to the data source. You will use this name when referring to the data source in other parts of your application, such as when you instantiate a MongoDB service client.


Consider a MongoDB cluster data source with the Realm Service Name myAtlasCluster. To create a service client in a function you would use the following code:

const myAtlasCluster ="myAtlasCluster");
MongoDB Connection String
Required for Atlas clusters. Not enabled for Data Lakes. A boolean indicating whether Realm should allow clients to connect to this cluster with a connection string over the wire protocol.
Read Preference
Required for Atlas clusters. Not available for Data Lakes. Specifies the read preference of the cluster. The default read preference (primary) should be sufficient for most use cases.

Once you've selected and configured a MongoDB cluster or Data Lake, click Save.

Realm will immediately begin the process of linking to the data source, which could take up to five minutes. Once Realm is finished linking to the data source, you can start working with the data.

For the most part, you can interact with a linked Data Lake just as you would with a linked Atlas cluster. However, there are some caveats to keep in mind when working with a Data Lake:

The following pages demonstrate how to start working with your linked data source from a function:


You can access your MongoDB data source remotely from a client. See the following sections of the Client Guides:

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