17-scaling-applications.md

Scaling NodeJS Applications

• single-thread mode
• event-driven paradigm to handle concurrency
• child processes to parallelize processing in multi-core CPU

Child processes always have three streams:

• child.stdin

• child.stdout

• child.stderr

• child.stdio

How to

• exec - Runs a command in a shell and buffers the output
• spawn - Lauches a new process with given command
• fork - Special case of spawn() to create NodeJS processes

Spawn

child_process.spawn(command[, args][, options])

const fs = require('fs');
const child_process = require('child_process');

for (let i = 0; i < 3; i++) {
  const workerProcess = child_process.spawn('node', ['support.js', i]);

  workerProcess.stdout.on('data', data => {
    console.log('stdout: ' + data);
  });

  workerProcess.stderr.on('data', data => {
    console.log('stderr: ' + data);
  });

  workerProcess.on('close', code => {
    console.log('child process exited with code ' + code);
  });
}

Exec

child_process.exec(command[, options], callback)

const fs = require('fs');
const child_process = require('child_process');

for (let i = 0; i < 3; i++) {
  const workerProcess = child_process.exec(
    `node support.js ${i}`,
    (error, stdout, stderr) => {
      if (error) {
        console.log(error.stack);
        console.log('Error code: ' + error.code);
        console.log('Signal received: ' + error.signal);
      }
      console.log('stdout: ' + stdout);
      console.log('stderr: ' + stderr);
    },
  );

  workerProcess.on('exit', function(code) {
    console.log('Child process exited with exit code ' + code);
  });
}

Fork

child_process.fork(modulePath[, args][, options])

const fs = require('fs');
const child_process = require('child_process');

for (let i = 0; i < 3; i++) {
  const workerProcess = child_process.fork('support.js', [i]);

  workerProcess.on('close', function(code) {
    console.log('child process exited with code ' + code);
  });
}