How to manage Node.js processes with PM2

PM2 is a process manager for Node.js applications that allows you to manage, monitor, and maintain applications in production.

Generally, when we develop Node.js applications, we run them directly with:

node app.js

But this has several problems in production. For example, if the application crashes, it won’t restart, we have no easy way to monitor the status, etc.

Installing PM2

To use PM2, we install it globally using NPM:

npm install -g pm2

Now we can verify that it has been installed correctly by running:

pm2 --version

Basic usage of PM2

Starting an application

The basic command to start an application with PM2 is:

pm2 start app.js

We can also specify a name for the application:

pm2 start app.js --name "my-api"

Essential commands

Here is a list of the main commands available in PM2.

And here is an example of its usage,

# Start application
pm2 start server.js --name "api-server"

# Check status
pm2 list

# View logs
pm2 logs api-server

# Stop application
pm2 stop api-server

# Delete application
pm2 delete api-server

Startup script

To ensure that PM2 starts automatically when the system reboots, we can do:

pm2 startup
pm2 save

This will create an appropriate startup script for your operating system.

Cluster mode

Node.js is single-threaded by default. PM2 allows you to easily create a cluster of processes:

pm2 start app.js -i max

This will create one instance for each available CPU, sharing the same port.

Monitoring and logs

PM2 includes a built-in monitor:

pm2 monit

Additionally, PM2 automatically manages the logs:

• ~/.pm2/logs/app-out.log: Standard logs
• ~/.pm2/logs/app-error.log: Error logs

Some commands

# View logs in real-time
pm2 logs

# Flush logs
pm2 flush

# Specific app logs
pm2 logs app-name

Advanced configuration with ecosystem files

For more complex configurations, PM2 supports configuration files (ecosystem.config.js):

module.exports = {
  apps: [{
    name: "api",
    script: "./src/index.js",
    instances: 2,
    exec_mode: "cluster",
    env: {
      PORT: 3000,
      NODE_ENV: "development"
    },
    env_production: {
      PORT: 80,
      NODE_ENV: "production"
    }
  }]
}