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Node.js v0.6.19 Manual & Documentación


Cluster#

Stability: 1 - Experimental

A single instance of Node runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node processes to handle the load.

The cluster module allows you to easily create a network of processes that all share server ports.

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

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

  cluster.on('death', function(worker) {
    console.log('worker ' + worker.pid + ' died');
  });
} else {
  // Workers can share any TCP connection
  // In this case its a HTTP server
  http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");
  }).listen(8000);
}

Running node will now share port 8000 between the workers:

% node server.js
Worker 2438 online
Worker 2437 online

This feature was introduced recently, and may change in future versions. Please try it out and provide feedback.

cluster.settings#

  • Object
    • exec String file path to worker file. (Default=__filename)
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

All settings set by the .setupMaster is stored in this settings object. This object is not supposed to be change or set manually, by you.

cluster.isMaster#

  • Boolean

True if the process is a master. This is determined by the process.env.NODE_UNIQUE_ID. If process.env.NODE_UNIQUE_ID is undefined, then isMaster is true.

cluster.isWorker#

  • Boolean

This boolean flag is true if the process is a worker forked from a master. If the process.env.NODE_UNIQUE_ID is set to a value, then isWorker is true.

Event: 'fork'#

  • worker Worker object

When a new worker is forked the cluster module will emit a 'fork' event. This can be used to log worker activity, and create you own timeout.

var timeouts = [];
var errorMsg = function () {
  console.error("Something must be wrong with the connection ...");
});

cluster.on('fork', function (worker) {
  timeouts[worker.uniqueID] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', function (worker) {
  clearTimeout(timeouts[worker.uniqueID]);
});
cluster.on('death', function (worker) {
  clearTimeout(timeouts[worker.uniqueID]);
  errorMsg();
});

Event: 'online'#

  • worker Worker object

After forking a new worker, the worker should respond with a online message. When the master receives a online message it will emit such event. The difference between 'fork' and 'online' is that fork is emitted when the master tries to fork a worker, and 'online' is emitted when the worker is being executed.

cluster.on('online', function (worker) {
  console.log("Yay, the worker responded after it was forked");
});

Event: 'listening'#

  • worker Worker object

When calling listen() from a worker, a 'listening' event is automatically assigned to the server instance. When the server is listening a message is send to the master where the 'listening' event is emitted.

cluster.on('listening', function (worker) {
  console.log("We are now connected");
});

Event: 'death'#

  • worker Worker object

When any of the workers die the cluster module will emit the 'death' event. This can be used to restart the worker by calling fork() again.

cluster.on('death', function(worker) {
  console.log('worker ' + worker.pid + ' died. restart...');
  cluster.fork();
});

Event: 'setup'#

  • worker Worker object

When the .setupMaster() function has been executed this event emits. If .setupMaster() was not executed before fork() this function will call .setupMaster() with no arguments.

cluster.setupMaster([settings])#

  • settings Object
    • exec String file path to worker file. (Default=__filename)
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

The setupMaster is used to change the default 'fork' behavior. It takes one option object argument.

Example:

var cluster = require("cluster");
cluster.setupMaster({
  exec : "worker.js",
  args : ["--use", "https"],
  silent : true
});
cluster.autoFork();

cluster.fork([env])#

  • env Object Key/value pairs to add to child process environment.
  • return Worker object

Spawn a new worker process. This can only be called from the master process.

cluster.settings#

  • Object
    • exec String file path to worker file. Default: __filename
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

All settings set by the .setupMaster is stored in this settings object. This object is not supposed to be change or set manually.

cluster.workers#

  • Object

In the cluster all living worker objects are stored in this object by there uniqueID as the key. This makes it easy to loop through all living workers.

// Go through all workers
function eachWorker(callback) {
  for (var uniqueID in cluster.workers) {
    callback(cluster.workers[uniqueID]);
  }
}
eachWorker(function (worker) {
  worker.send('big announcement to all workers');
});

Should you wish to reference a worker over a communication channel, using the worker's uniqueID is the easiest way to find the worker.

socket.on('data', function (uniqueID) {
  var worker = cluster.workers[uniqueID];
});

Class: Worker#

A Worker object contains all public information and method about a worker. In the master it can be obtained using cluster.workers. In a worker it can be obtained using cluster.worker.

worker.uniqueID#

  • String

Each new worker is given its own unique id, this id is stored in the uniqueID.

While a worker is alive, this is the key that indexes it in cluster.workers

worker.process#

  • ChildProcess object

All workers are created using child_process.fork(), the returned object from this function is stored in process.

See: Child Process module

worker.suicide#

  • Boolean

This property is a boolean. It is set when a worker dies, until then it is undefined. It is true if the worker was killed using the .destroy() method, and false otherwise.

worker.send(message, [sendHandle])#

  • message Object
  • sendHandle Handle object

This function is equal to the send methods provided by child_process.fork(). In the master you should use this function to send a message to a specific worker. However in a worker you can also use process.send(message), since this is the same function.

This example will echo back all messages from the master:

if (cluster.isMaster) {
  var worker = cluster.fork();
  worker.send('hi there');

} else if (cluster.isWorker) {
  process.on('message', function (msg) {
    process.send(msg);
  });
}

worker.destroy()#

This function will kill the worker, and inform the master to not spawn a new worker. To know the difference between suicide and accidentally death a suicide boolean is set to true.

cluster.on('death', function (worker) {
  if (worker.suicide === true) {
    console.log('Oh, it was just suicide\' – no need to worry').
  }
});

// destroy worker
worker.destroy();

Event: 'message'#

  • message Object

This event is the same as the one provided by child_process.fork(). In the master you should use this event, however in a worker you can also use process.on('message')

As an example, here is a cluster that keeps count of the number of requests in the master process using the message system:

var cluster = require('cluster');
var http = require('http');

if (cluster.isMaster) {

  // Keep track of http requests
  var numReqs = 0;
  setInterval(function() {
    console.log("numReqs =", numReqs);
  }, 1000);

  // Count requestes
  var messageHandler = function (msg) {
    if (msg.cmd && msg.cmd == 'notifyRequest') {
      numReqs += 1;
    }
  };

  // Start workers and listen for messages containing notifyRequest
  cluster.autoFork();
  Object.keys(cluster.workers).forEach(function (uniqueID) {
    cluster.workers[uniqueID].on('message', messageHandler);
  });

} else {

  // Worker processes have a http server.
  http.Server(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");

    // notify master about the request
    process.send({ cmd: 'notifyRequest' });
  }).listen(8000);
}

Event: 'online'#

  • worker Worker object

Same as the cluster.on('online') event, but emits only when the state change on the specified worker.

cluster.fork().on('online', function (worker) {
  // Worker is online
};

Event: 'listening'#

  • worker Worker object

Same as the cluster.on('listening') event, but emits only when the state change on the specified worker.

cluster.fork().on('listening', function (worker) {
  // Worker is listening
};

Event: 'death'#

  • worker Worker object

Same as the cluster.on('death') event, but emits only when the state change on the specified worker.

cluster.fork().on('death', function (worker) {
  // Worker has died
};