The cluster nodes stats API allows to retrieve one or more (or all) of the cluster nodes statistics.
$ curl -XGET 'http://localhost:9200/_cluster/nodes/stats'
$ curl -XGET 'http://localhost:9200/_cluster/nodes/nodeId1,nodeId2/stats'
The first command retrieves stats of all the nodes in the cluster. The second commands selectively retrieves nodes stats of only nodeId1 and nodeId2.