Read-only nodes are replicas of a cluster’s primary node located in additional geographical regions. Using read-only nodes reduces latency for users connecting from those regions.
Communication between primary and read-only nodes is SSL-encrypted and sent over the public network.
To add a read-only node, click on the name of the cluster to go to its Overview. At the bottom of the page, in the Read Only Nodes section, click the Add a read-only node link.
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 and access read-only nodes using a command-line client and the connection string in the node’s Overview page.