Standby nodes maintain a copy of the primary node in the cluster. In the event that the primary node fails, a standby node will be automatically promoted to replace it. Standby nodes are necessary for a high availability cluster configuration.
Standby nodes differ from read-only nodes, which provide geographically distinct horizontal read scaling.
You can add up to two standby nodes to a cluster, either during creation when you choose the cluster configuration or after creation on the cluster’s Settings tab.
From the Databases overview page, open the cluster’s More menu and select Settings.
In the Cluster configuration section, click Edit.
Open the Standby Nodes dropdown and choose the number of standby nodes.
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.