cloudwatchのアラームからecsのインスタンス数を増やすaws lambdaスクリプト

a.js

console.log('Loading event');
var aws = require('aws-sdk');
 
exports.handler = function(event, context) {
  var cluster = 'maeno-test'
  var ecsService = 'test-service';
  var ecsRegion = 'ap-northeast-1';
  var maxCount = 3;
 
  var ecs = new aws.ECS({region: ecsRegion});
  ecs.describeServices({services:[ecsService],cluster:cluster}, function(err, data) {
    if (err) {
      console.log(err, err.stack);
    } else {
      var desiredCount = data.services[0].desiredCount;
      if (desiredCount < maxCount) {
        desiredCount++;
        var params = {
          cluster:      cluster,
          service:      ecsService, 
          desiredCount: desiredCount
        };
        ecs.updateService(params, function(err, data) {
          if (err) {
            console.log(err, err.stack);
          } else {
            console.log(data);
            context.succeed();
          }
        });
      } else {
        console.log('Service count is already max.');
        context.fail();
      }
    }
  });
};