simple multicore usage in Nodejs

require('./bootstrap');
var cluster = require('cluster');
var numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
    for (var i = 0; i < numCPUs; i++) {
        cluster.fork();
    }

    console.log('[CLUSTER] Worker' + (numCPUs > 1 ? 's': '') + ' count: "' + numCPUs.toString() + '"');

    cluster.on('exit', function (worker) {
        'use strict';

        console.log('[RIP] Worker "' + worker.process.pid + '" died.');
        cluster.fork();
        console.log('[CPR] Worker recovered.');
    });
} else {
    // each worker run this server
    // you can change this to what ever your app entry file is
    require('./app.js');
}

Please, what is in ./bootstrap ?
Can i pass to app.js some parameter which tells it forked number / which forked number it is?