AWS Lambda Method to return CloudWatch metrics as JSON

cloudwatch-lambda.js

'use strict';
var AWS = require('aws-sdk');
var cloudwatch = new AWS.CloudWatch({apiVersion: '2010-08-01'});

function getMetric(metricName, callBack) {
    var now =  new Date();
    var anHourAgo = new Date()
    anHourAgo.setHours(now.getHours()-1);
    
    var params = {
      StartTime: anHourAgo,
      EndTime: now,
      MetricName: metricName,
      Namespace: 'SchoolStats',
      Period: 3600,
      Statistics: [  'Average' ]
    };
    
    cloudwatch.getMetricStatistics(params, function(err, data) {
        if (err) {
            console.log(err, err.stack); // an error occurred
            callBack(metricName, undefined);
        } else {
            callBack(metricName, data.Datapoints[0].Average);
        }
    });
    
}

exports.handler = (event, context, callback) => {
    var metrics = ['ActiveSchools', 'Observations', 'ActiveChildren'];
    var results = {};
    var number_of_metrics_awaited = metrics.length;
    
    function recordMetric(metricName, count) {
        results[metricName] = count;
        number_of_metrics_awaited--;
        if(number_of_metrics_awaited === 0) {
            sendResults(results);
        }
    }
    
    function sendResults(results) {
        var response = {
            statusCode: 200,
            headers: {},
            body: JSON.stringify(results)
        };
        console.log("response: " + JSON.stringify(response))
        context.succeed(response);
    }
    
    metrics.forEach(function(metricName) { getMetric(metricName, recordMetric); });
};