Any node which is neither a master (node.master is set to false) nor data (node.data is set to false) becomes the client node. Being the client node, it behaves as a load balancer that routes the requests and search to the right nodes. In general, this type of node existing in a cluster is not really required because Data Node would be able to do these themselves. However, a big installation having dedicated nodes would reduce the additional work being done by other important nodes within the cluster.
The following figure shows all the types of nodes within an Elasticsearch cluster:
Figure 16: Different types of ...
