使用 PM2 的 Nodejs 应用程序的启动顺序

Question

I am using the command pm2 start apps.json to start multiple apps in a single command. These apps are defined in apps.json :

{
  "apps": [
    {
      "name": "foo",
      "script": "./foo.js",
    },
    {
      "name": "bar",
      "script": "./bar.js",
    },
    {
      "name": "baz",
      "script": "./baz.js",
    }
  ]
}

Question: Is it possible to define the startup sequence, such that foo.js has to finish starting first before bar.js and baz.js can start?

For example, foo.js can perform a graceful start , running process.send('ready') to change its pm2 status to online . Only then will bar.js and baz.js be started by pm2. This will be similar to Docker Compose's depend_on parameter.

Answer 1

No such thing can be done via the configuration file only, but PM2 has a programmatic api which allows you to perform IPC (Inter-Process communication).

The following methods are the ones to work with:

• pm2.list To list the processes that are running and get their names / IDs
• pm2.launchBus For the processes that will receive information and react in consequence
• pm2.sendDataToProcessId For sending informations to another process

This way you can run multiple scripts and make one wait for another. Once a script recieve a message on the message bus , it can start a process with pm2.start

Here's a piece of PSEUDO-CODE to illustrate my point:

const pm2 = require('pm2');

pm2.connect(() => {
  pm2.list(function(err, processes) {
    const fooProcess = processes.find(p => p.name == 'foo');

    pm2.launchBus((err, bus) => {
      bus.on('process:msg', packet => {
        if (packet.startBar === true) {
          pm.start({ script: 'bar.js' }, (err, apps) => { ... })
        }
      });
      bus.on('error', console.error);
    });
  });
});

In another script, you would have the following:

pm2.sendDataToProcessId(barProcessID, {
  data : { startBar : true },
  topic: 'process:msg'
}, (err, res) => console.log(err, res));

Best regards

Answer 2

A little hack, you can write: "start": "pm2 start server.js && pm2 start server1.js" inside package.json . If you'd run it as npm start, it'll run the start script, similarly, you can create the script to stop it.

If not then you can also use child_process [it comes by default with nodejs] to run commands from inside your script by using childProcess.exec('pm2 start server.js && pm2 start server1.js');