How does the PM2 process manager help manage Node.js servers in production, and what is Zero-Downtime Reload?

Short answer

PM2 manages the application in Cluster mode, restarts it after a crash, and enables updates without interruption by restarting processes one at a time.

Explanation

PM2 provides a complete process manager for Node.js on traditional and virtual servers. When you run pm2 reload, it signals the first process to shut down gracefully, waits for the replacement process to start and listen on the port, then moves to the next one. This keeps requests flowing without dropping connections.

Code example

// ecosystem.config.js
module.exports = {
  apps: [{
    name: "api",
    script: "./dist/index.js",
    instances: "max",
    exec_mode: "cluster"
  }]
};

Common mistakes

• Using pm2 restart instead of pm2 reload during updates, temporarily interrupting service for all users.

Follow-up questions

• How do you use multiple CPU cores with Node.js's node:cluster module?

Sources

• PM2 docs — Quick Start