nodesToHostCallback for the elasticsearch.js client that filters out nodes which are not in "client" mode.

only_client_nodes.js

var elasticsearch = require('elasticsearch');
var baseNodesToHostCallback = require('elasticsearch/src/lib/nodes_to_host');

var client = new elasticsearch.Client({
  /* host seed list */
  hosts: [ ... ],
  
  // sniff every 5 minutes
  sniffInterval: 1000 * 60 * 5,
  
  // filter out non-client nodes, then pass
  // to the default handler which parses and
  // normalizes node list
  nodesToHostCallback: function (nodes) {
    return baseNodesToHostCallback(nodes.filter(function (node) {
      var neverMaster = node.attributes && node.attributes.master === 'false';
      var isClientNode = neverMaster && node.attributes.data === 'false';
      return isClientNode;
    }));
  }
});