# How to Add Standby Nodes to MongoDB Database Clusters

MongoDB is a source-available cross-platform document-oriented database program for high-volume storage. Classified as a NoSQL database program, MongoDB uses JSON-like documents with optional schemas.

In a database cluster, standby nodes maintain a copy of the primary node. If the primary node fails, a standby node is automatically promoted to replace it. Additionally, standby nodes can direct routing for read traffic.

MongoDB clusters can only have two standby nodes at this time. This is necessary for a [high availability cluster configuration](https://docs.digitalocean.com/products/databases/index.html.md#high-availability). For more information about MongoDB’s high availability cluster architecture, see [MongoDB’s official documentation](https://docs.mongodb.com/manual/replication/).

You can add standby nodes during cluster creation in the [cluster configuration section](https://docs.digitalocean.com/products/databases/mongodb/how-to/create/index.html.md#choose-a-cluster-configuration) of the create page.

You can also add standby nodes to an existing database cluster. From the **Databases** page, click the name of the cluster to go to its **Overview** page, then click the **Settings** tab.

![Screenshot of cluster settings page](https://docs.digitalocean.com/screenshots/databases/cluster-settings-page.1436bb24fe70137f02b3682bebce26cb95fa67f2c599884382912108a53489ea.png)

On the **Settings** page, in the **Cluster configuration** section, click **Edit**. Open the **Standby Nodes** drop-down and choose the number of standby nodes.

![Screenshot of Add Standby Nodes](https://docs.digitalocean.com/screenshots/databases/mongodb-add-standby.632bc629cee998e02009b794d6e62650ee2c4762909965e40c85ff35aafe6a6b.png)

When you’re done, click **Save** to immediately provision the standby nodes. The time to complete varies depending on the size of the primary node and its data, but we recommend allowing at least 5 minutes.