Access worker environment from master (Node.js Cluster)

Question

I fork workers in my Node.js application via the Cluster module and pass a custom ID to the environment of all my workers. That works well for far.

However, I do not know how I can access this id in my master when an 'online' or 'exit' event is emitted.

The documentation is not very helpful. Could you please point me the right way?

var cluster = require('cluster'); 

if (cluster.isMaster) {
  //MASTER

  function fork() {
    var worker_env = {worker_id:'my_custom_id'};
    cluster.fork(worker_env);
  }                 

  cluster.on('online', function(worker) {
    console.log(worker.process.env.worker_id); // undefined
    //
    // How can I access my custom worker id here?
    //
  });

  cluster.on('exit', function(worker, code, signal) {
    //
    // And here...?
    //
    fork();
  });

} else {
  // WORKER

  console.log(process.env.worker_id); // my_custom_id
}

score 3 · Accepted Answer · answered Feb 19 '14 at 16:00

theres no way, the worker process env is not exposed to the master.

One aproach can be a map of our cluster (a object containig the needed info).

Something like these:

var cluster = require('cluster');

if (true === cluster.isMaster) {
  //CODE EXECUTED BY MASTER
  var cluster_map = {}; // Here we store the workers info in a object   
  var restart_Limit = 10; // max global worker restart (10)

  function fork_worker(myWorkerId) {
    // these makes worker_id available in the worker
    var worker = cluster.fork({
      worker_id: myWorkerId 
    });
    // max restarts limit (global)
    if (worker.id >= restart_Limit) { 
      console.log('Restart limit reached, bye!');
      process.kill();

    }
    // here we add the key "myWorkerId"  to the cluster map
    cluster_map[worker.id] = myWorkerId;

    // WORKER AUTO-KILL
    setTimeout(function() {
      console.log('stoping...' + myWorkerId);
      worker.kill();
    }, 3000);
  }

  cluster.on('online', function(worker) {
    var online_proc = cluster_map[worker.id];

    console.log('worker online: ' + online_proc + '\n Restarts: ' + worker.id);
  });

  cluster.on('exit', function(worker, code, signal) {

    var exited_proc = cluster_map[worker.id];

    // delete the process from the cluster map
    delete cluster_map[worker.id];
    console.log("worker offline: " + exited_proc);

    // WORKER AUTO-RESTART
    setTimeout(function() {
      console.log('Restarting... ' + exited_proc);
      fork_worker(exited_proc);
    }, 3000);

  });

  // start the magic ( 3 workers )
  (function() {
    fork_worker('id_1');
    fork_worker('id_2');
    fork_worker('id_3');
  })();

} else {
  //CODE EXECUTED BY EACH WORKER (process env is present here).
  console.log('hi from the worker,  process.env: ' + process.env.worker_id);
  // all the hard work for the workers here.
}

Thank you, also for the example. Will do it this way. – 1nsane Feb 19 '14 at 21:56 — 1nsane, Feb 19 '14 at 21:56

Access worker environment from master (Node.js Cluster)

1 Answers1