AWS Lambda and NodeJS Cluster

I wrote this short example to test clustering in AWS lambda. Can someone tell me where I went wrong? The number of cores returns 2, but the message is never passed.

'use strict';
var cluster = require('cluster');  
var http    = require('http');  
var os      = require('os');

var numCPUs = os.cpus().length;

exports.test = (event, context, callback) => {
    console.log('Number of Cores : ', numCPUs);
    if (cluster.isMaster) {
        for (var i = 0; i < numCPUs; ++i) {
            cluster.fork();
        }
        for (const id in cluster.workers) {
            cluster.workers[id].on('message', messageHandler);
        }
    } else {
        process.send('running');
    }
};

function messageHandler(msg) {
    console.log(msg);
}

via Ross Bassett