title: Access worker environment from master (Node.js Cluster)
body: <p>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.</p>
  
  <p>However, I do not know how I can access this id in my master when an 'online' or 'exit' event is emitted. </p>
  
  <p>The documentation is not very helpful. Could you please point me the right way?</p>
  
  <pre><code>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
  }
  </code></pre>