Read-only nodes let you place replicas of your cluster’s primary node in additional geographical regions to reduce latency for users in those regions.
Read-only nodes differ from standby nodes, which are exact copies of the primary node that are automatically moved into place in the event of a primary node failure.
To add a read-only node, click on the name of the cluster to go to its Overview, then click the Add a read-only node link at the bottom of the page.
Select the size, which must be equal to or larger than the primary node, then select the datacenter and name the node. When you’re done, click Create a read-only node to provision the node.
Like primary nodes, you can limit access to a read-only nodes to trusted sources. To access read-only nodes, use their specific connection details.