Node.js PM2 Orchestration Explained

Process managers enhance Node.js applications by allowing:

• Monitoring running services locally and in production
• Running system administration tasks like starting and stopping applications without downtime (a.k.a. orchestration)
• Logging metrics
• Load balancing

To get started, create a simple server using Express.js:

$ npm init -y
...\Mirza\first-pm2-app\package.json:

{
"name": "first-pm2-app",
"version": "1.0.0",
"description": "",
"main": "app.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC"
}

$ npm install express

With basic packages set up, create an app.js file and paste the following code:

// app.js
const app = require("express")();

app.get("/", (req, res) => {
  res.send("hello world");
});

app.listen(3000, () => {
  console.log("Server started on port 3000!");
});

PM2 is an NPM package installed globally on the system:

npm install -g pm2

...and is then used to run JavaScript projects on your system, just like using the node command:

pm2 start app.js

Notice that we didn't get the log Server started on port 3000! printed as would normally happen when running node app.js.

Moreover, PM2 kicked us out of the long-running loop. If you go to localhost:3000, you can verify that the server is up.

The server is up and running in the background.

PM2 lets you manually start, list, and stop active processes.

You can list out the running PM2 servers: pm2 list.

You can stop a single server: pm2 stop app.js or via index pm2 stop 0.

Or all at once: pm2 stop all.

You can delete a saved (cached) server configuration: pm2 delete app or pm2 delete 0.

Or all at once: pm2 delete all.

Just like with Nodemon, you can reload the server on changes: pm2 app.js --watch.

Instead of running the Node.js application via node app.js, use pm2 start app.js. By running the app like this, PM2 will automatically recover the app from crashes - simply put, it automatically restarts the server if it fails.

By default, even if you're running the app on a multi-core CPU (server), Node.js runs an application on a single CPU core. If you have high traffic, all requests go to one CPU instance while the rest are doing nothing.

The idea behind load balancing is to distribute traffic across multiple cores:

• pm2 start app.js -i 2
• pm2 start app.js -i 4
• pm2 start app.js -i 8
• pm2 start app.js -i max

Node.js uses a specific pattern for load balancing, where all requests go to one core (master process), and if it gets occupied, it automatically distributes requests to other cores (processes). If request count drops, so do occupied cores.

The result is an app that can handle large traffic.

Running pm2 monit app.js lets you monitor the stats of your application (CPU and memory usage) and display logs in real time.

Additionally, you can display logs per process or application:

• pm2 logs <processname>
• pm2 logs <app-name>

PM2 lets you monitor metrics on their main website.

Start by registering the app using the official guide.

Once linked with the official PM2 Keymetrics site, you should see your app metrics displayed.

PM2 is a powerful process manager that helps you orchestrate your applications using a few commands, while you, like Joe, are resting on the beach somewhere in Hawaii. For more on PM2, be sure to check the official docs.

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Bye for now.