sahara/etc/rest-api-samples/scale_cluster.json

{
    "add_node_groups":[
        {
            "node_group_template_id": "9e1225e0-b7ce-425b-9555-3a61166167c8",
            "count":1,
            "name": "test_ng"
        }
    ],
    "resize_node_groups":[
        {
            "name" : "worker",
            "count":2
        }
    ]
}