How can we configure master process when using PM2

Question

I have an problem with PM2 in NodeJS. Without PM2, we always have some lines of code like below to configure master process

if(cluster.isMaster){
    //master process configuration
} else {
    //worker process configuration
}

Exactly, I want to send message from a worker to master, then, master will send back a message to all workers for notification an event.

Actually, I saw that, no lines of code in master process configuration runs when using PM2.

Many thanks for any idea about this issue !

Answer 1

With PM2, you usually don't have to use this constuction. Typically, it looks like the following:

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

if(cluster.isMaster){
  for (var i = 0; i < numCPUs; ++i) {
    cluster.fork();
  }
} else {
  http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world");
  }).listen(8080);
}

With PM2 the equivalent for the above is:

var http = require('http');

http.createServer(function(req, res) {  
  res.writeHead(200);
  res.end("hello world");
}).listen(8080);

pm2 start app.js -i <number of instances>

you can read up more on the topic here

Update: You can try to distinguish between master and slave by passing command line arguments. Here is an example ecosystem.json:

{
  "apps" : [
    {
      "name": "Master",
      "script": "app.js",
      "args": ["master"],
      "instances": "1",
    },
    {
      "name": "Slave",
      "script": "app.js",
      "args": ["slave"],
      "instances": "3"
    }
  ],
...

Then you can do the following:

argv = process.argv.slice(2) //stripe 'node', 'app.js' away

if (argv[0] === 'master'){
   // ...
} else {
  // ...
}