What is PM2 and how to manage Node.js processes in production?

Process Management in Node.js

In production, you need to ensure your Node.js application:

Stays running if it crashes (auto-restart)
Utilizes all CPU cores (cluster mode)
Can be monitored (logs, metrics)
Can be deployed without downtime (zero-downtime reload)

PM2 is the most popular production process manager for Node.js.

Why Not Just `node server.js`?

Problem	Without PM2	With PM2
App crashes	Process dies, stays dead	Auto-restarts
Multi-core	Uses 1 core only	Cluster mode (all cores)
Logging	Goes to stdout, lost	Persisted log files
Deploy	Downtime during restart	Zero-downtime reload
Monitoring	None built-in	CPU, memory, restarts

Getting Started with PM2

bash

# Install globally
npm install -g pm2

# Start application
pm2 start server.js

# Start with options
pm2 start server.js --name "my-api" -i max  # cluster mode, all CPUs

# List running processes
pm2 list

# Monitor in real-time
pm2 monit

# View logs
pm2 logs
pm2 logs my-api --lines 100

Ecosystem File (ecosystem.config.js)

module.exports = {
  apps: [{
    name: 'my-api',
    script: 'dist/main.js',
    instances: 'max',        // Use all CPU cores
    exec_mode: 'cluster',    // Cluster mode
    max_memory_restart: '1G',
    env: {
      NODE_ENV: 'production',
      PORT: 3000
    },
    env_staging: {
      NODE_ENV: 'staging',
      PORT: 3001
    }
  }]
};

bash

# Start with ecosystem file
pm2 start ecosystem.config.js

# Start for specific env
pm2 start ecosystem.config.js --env staging

Key PM2 Commands

Command	Description
`pm2 start app.js`	Start
`pm2 stop app`	Stop
`pm2 restart app`	Restart
`pm2 reload app`	Zero-downtime reload
`pm2 delete app`	Remove from PM2
`pm2 list`	List all processes
`pm2 monit`	Real-time dashboard
`pm2 logs`	View logs
`pm2 save`	Save process list
`pm2 startup`	Auto-start on boot

Cluster Mode

PM2 cluster mode spawns multiple instances of your app, distributing load across CPU cores:

bash

# Start 4 instances
pm2 start server.js -i 4

# Start on all available CPUs
pm2 start server.js -i max

# Scale up/down
pm2 scale my-api +2  # Add 2 more instances
pm2 scale my-api 2   # Set to exactly 2

Zero-Downtime Deployment

bash

# Reload gracefully (one by one in cluster mode)
pm2 reload my-api

# Deployment workflow
pm2 deploy ecosystem.config.js production setup
pm2 deploy ecosystem.config.js production

Alternatives to PM2

Tool	Use Case
Docker	Container-based deployment
systemd	Linux service management
Kubernetes	Container orchestration at scale
nodemon	Development only (not production)
forever	Simple process manager (legacy)

Production recommendation: Use PM2 for simple deployments on VPS. For microservices at scale, consider Docker + Kubernetes with proper health checks and auto-scaling.

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