quick UDP Logstash logging from nodejs

logstashUDP.js

var util = require('util');
var dgram = require('dgram');

function logstashUDP(host, port, type, message, fields, callback) {
  var client = dgram.createSocket('udp4');
  var logObject = {
    '@timestamp': (new Date).toISOString(),
    type: type,
    message: message,
    fields: fields
  };
  var m = new Buffer(JSON.stringify(logObject));
  client.send(m, 0, m.length, port, host, function(err, bytes) {
    client.close();
    callback(err);
  });
}

logstashUDP('127.0.0.1', 10001, 'js', 'hello world', {'level': 'debug'}, function(err) {
  if(err) {
    console.log('Error logging: %s', util.inspect(err));
  }
});

How do we specify an index?