PM2 Guide: Running Node.js Apps in Production

The short answer: why PM2

If you start an app with node server.js, it stops when you close the terminal, hit an error or reboot the server. PM2 is a process manager for Node.js that:

• keeps the app running in the background and restarts it on crashes;
• runs several copies across CPU cores (cluster mode);
• reloads code without downtime;
• brings processes back after a server restart;
• collects logs and shows resource usage.

Install and first run

npm install -g pm2
pm2 start server.js --name api

Core commands:

An ecosystem file instead of long commands

Keep settings in the repository, in ecosystem.config.js:

module.exports = {
  apps: [
    {
      name: "api",
      script: "./dist/server.js",
      instances: "max",
      exec_mode: "cluster",
      max_memory_restart: "500M",
      env: {
        NODE_ENV: "production",
        PORT: 3000,
      },
    },
  ],
};

Start it with pm2 start ecosystem.config.js. The configuration is then identical on every server and tracked in Git. Do not put secrets in this file — pass them via the server's environment variables or a .env file that is not committed.

Cluster mode

Node.js runs JavaScript on a single thread, so one process uses one core. In cluster mode PM2 starts several instances and distributes incoming connections between them. instances: "max" means one per core.

Key conditions:

• the app must be stateless: sessions, cache and queues live in external storage (Redis, a database), not in process memory;
• scheduled jobs inside the app will run in every instance — move them out or run them in only one;
• WebSockets in a cluster need sticky sessions or an external adapter.

Zero-downtime reload

pm2 reload api restarts instances one at a time: while one reloads, the others keep serving requests. This works in cluster mode. To make reloads truly smooth:

• handle the SIGINT signal — close the server and database connections cleanly;
• if needed, use wait_ready: true and process.send("ready") so PM2 waits until the app is actually ready.

Startup on boot

pm2 startup
# run the command PM2 prints
pm2 save

pm2 startup creates a system service and pm2 save stores the current process list. Run pm2 save again after adding or removing apps.

Managing logs

By default logs go to ~/.pm2/logs and are never deleted. Install the rotation module:

pm2 install pm2-logrotate
pm2 set pm2-logrotate:max_size 50M
pm2 set pm2-logrotate:retain 10

Otherwise logs will eventually fill the disk.

PM2 or Docker

With one VPS and one or two Node.js apps, PM2 is a simple and reliable choice. As the project grows, with several services and a need for reproducible environments, move to Docker. Inside a container you usually do not need PM2: Docker or the orchestrator handles restarts, and multiple copies run as separate containers.