A detailed introduction to the multi-process module Cluster in Node.js and how to use it

It is well known that Node.js is single-threaded, and a single Node.js process cannot fully utilize multiple cores. Starting from v0.6.0, Node.js has added a cluster module, which makes it easy to make full use of multi-core machines when developing web services with Node.js. This article mainly introduces you to the relevant information about the multi-process module Cluster in Node.js. Friends who need it can refer to it

Preface

We all know that the biggest feature of nodejs is single-process, non-blocking operation, and asynchronous event-driven. These features of Nodejs can solve some problems very well. For example, in server development, concurrent request processing is a big problem, and blocking functions will cause resource waste and time delay. Through event registration and asynchronous functions, developers can improve resource utilization and performance will be improved. Since Node.js adopts single-process and single-thread mode, in today's environment where multi-core hardware is popular, how can Nodejs, which has excellent single-core performance, take advantage of multi-core CPUs? Founder Ryan Dahl recommends running multiple Nodejs processes and using some communication mechanism to coordinate tasks. Currently, many third-party Node.js multi-process support modules have been released, and NodeJS versions 0.6.x and above provide a cluster module that allows the creation of a group of processes that "share the same socket" to share the load pressure. .

This article is based on the cluster module to describe Node.js programming under multi-core CPU.

Cluster module introduction

The cluster module provided by nodejs is still in the experimental stage. We can see it in the official document of v0.10.7 The release information to the module is as follows:

Stability: 1 - Experimental

Regarding the function of this module, the source document describes this: "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." This means: Node examples run in single-process mode, and sometimes in order to make full use of the resources of a multi-core system, users need to run a group of Node processes to share the load.

Cluster usage introduction

First post a sample application code of this module, and then conduct a detailed analysis, the code is as follows:

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

if (cluster.isMaster) {
 require('os').cpus().forEach(function(){
 cluster.fork();
 });
 cluster.on('exit', function(worker, code, signal) {
 console.log('worker ' + worker.process.pid + ' died');
 });
 cluster.on('listening', function(worker, address) { 
 console.log("A worker with #"+worker.id+" is now connected to " +
  address.address +
 ":" + address.port); 
 }); 
} else {
 http.createServer(function(req, res) {
 res.writeHead(200);
 res.end("hello world\n");
 console.log('Worker #' + cluster.worker.id + ' make a response');
 }).listen(8000);
}

This code is very simple. The main thread is the currently running js file. The main thread creates child processes based on the number of cores of your local system. All processes share a listening port 8000. When a request is initiated, the main thread will randomly assign the request to a child process. console.log('Worker #' + cluster.worker.id + ' make a response');This code can print out which process handles the request.

Problem Analysis

#We mentioned earlier that when a request is initiated, the system determines which process the request will be handed over for processing. This type of load balancing that relies entirely on the system has an important flaw: on Windows, Linux and Solaris, as long as the accept queue of a certain sub-process is empty (usually the last sub-process created), the system will use multiple connections Assigned to the same sub-process, this will cause extremely uneven load among processes. Especially when using long connections, the number of new coming connections per unit time is not high, and the accept queue of the child process is often empty, which will cause connections to be continuously allocated to the same process. Therefore, this kind of load balancing completely depends on the idleness of the accept queue. Load balancing can only be achieved when short connections are used and the concurrency is very high. However, at this time, the system load will be very high and the system will become unstable. stand up.

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