How to run Cron Job in Node.js application that uses cluster module?

Question

I\'m using node-cron module for scheduling tasks in Node.js application. I also want run the application in several processes using core cluster module.

Running applica

Answer 1

I actually do not like the redis approach that is also used in the cron-cluster npm plugin, because I do not want to have that redis server running on my maschine and maintain it, too.

I would like to discuss this approach with you:

Pro: we do not need to use redis Con: cron jobs are always running on the same worker

I use the message passing only for this, if you use it for other things, you want to pass the information that

if (cluster.isMaster) {
    // Count the machine's CPUs
    var cpuCount = require('os').cpus().length;;

    // Create a worker for each CPU
    for (var i = 0; i < cpuCount; i += 1) {
        cluster.fork();
    }

    cluster.on('fork', (worker) => {
        console.log("cluster forking new worker", worker.id);
    });

    // have a mainWorker that does the cron jobs.
    var mainWorkerId = null;

    cluster.on('listening', (worker, address) => {
        console.log("cluster listening new worker", worker.id);
        if(null === mainWorkerId) {
            console.log("Making worker " + worker.id + " to main worker");
            mainWorkerId = worker.id;
        worker.send({order: "startCron"});
        }
    });

    // Listen for dying workers if the mainWorker dies, make a new mainWorker
    cluster.on('exit', function (worker, code, signal) {
        console.log('Worker %d died :(', worker.id);

        if(worker.id === mainWorkerId) {
            console.log("Main Worker is dead...");
            mainWorkerId = null;
        }

        console.trace("I am here");
        console.log(worker);
        console.log(code);
        console.log(signal);
        cluster.fork();

    });
// Code to run if we're in a worker process
} else {

    // other code like setup app and stuff

    var doCron = function() {
        // setup cron jobs...
    }

    // Receive messages from the master process.
    process.on('message', function(msg) {
        console.log('Worker ' + process.pid + ' received message from master.', message);
        if(message.order == "startCron") {
            doCron();
        }
    });
}