Generally, a node is represented by a replica in the Qbox dashboard, at larger RAM sizes replicas are broken up into multiple node instances. The purpose of adding replicas is either to support a higher request load or to add stability to a production cluster.
In the Qbox dashboard, you can add or remove replicas by accessing the management page for a specific cluster. When adding a replica, you can expect 1-2 minutes of downtime for clusters with less than 2 replicas. We recommend having 2 replicas for any production cluster, this will allow your cluster to continue to serve search and indexing requests in the case of a downed node.