Adding a node to or removing a node from an existing Elasticsearch cluster
You can add nodes to any Elasticsearch cluster. Removing a node is possible only if the cluster has at least four nodes.
Before you begin
curl -X GET 'http://primary_node_ip:9200/_cluster/state?pretty'
curl -X GET 'http://primary_node_ip:9200/_nodes?pretty'
Where primary_node_ip is the IP address of either the single Elasticsearch node or the primary Elasticsearch node in a cluster of at least three nodes.