HXavS.dev

PM2

[PM2] is a daemon process manager that will help you manage and keep your application online. Getting started with PM2 is straightforward, it is offered as a simple and intuitive CLI.

#Getting Started

#Install

The latest PM2 version is installable with NPM or Yarn

$ npm install pm2@latest -g

OR

$ yarn global add pm2

#Start an app

The simplest way to start, daemonize and monitor your application is by using this command line

$ pm2 start app.js

Or start any other application easily

$ pm2 start bashscript.sh
$ pm2 start python-app.py --watch
$ pm2 start binary-file -- --port 1520

#Some options you can pass to the CLI

Specify an app name

--name <app_name>

Watch and Restart app when files change

--watch

Set memory threshold for app reload

--max-memory-restart <200MB>

Specify log file

--log <log_path>

Pass extra arguments to the script

-- arg1 arg2 arg3

Delay between automatic restarts

--restart-delay <delay in ms>

Prefix logs with time

--time

Do not auto restart app

--no-autorestart

Specify cron for forced restart

--cron <cron_pattern>

Attach to application log

--no-daemon

#Managing processes

Managing application state is simple here are the commands

$ pm2 restart app_name
$ pm2 reload app_name
$ pm2 stop app_name
$ pm2 delete app_name

#Instead of app_name you can pass

  • all to act on all processes
  • id to act on a specific process id

#Check status, logs, metrics

Now that you have started this application, you can check its status, logs, metrics and even get the online dashboard with pm2.io.

List the status of all application managed by PM2

$ pm2 [list|ls|status]

To display logs in realtime

$ pm2 logs

To dig in older logs

$ pm2 logs --lines 200

Here is a realtime dashboard that fits directly into your terminal

$ pm2 monit

Web based dashboard, cross servers with diagnostic system

$ pm2 plus

#Cluster mode

For Node.js applications, PM2 includes an automatic load balancer that will share all HTTP[s]/Websocket/TCP/UDP connections between each spawned processes.

To start an application in Cluster mode

$ pm2 start app.js -i max

Read more about cluster mode here.

#Ecosystem File

You can also create a configuration file, called Ecosystem File, to manage multiple applications. To generate an Ecosystem file

$ pm2 ecosystem

This will generate an ecosystem.config.js file

module.exports = {
  apps : [{
    name: "app",
    script: "./app.js",
    env: {
      NODE_ENV: "development",
    },
    env_production: {
      NODE_ENV: "production",
    }
  }, {
     name: 'worker',
     script: 'worker.js'
  }]
}

And start it easily

$ pm2 start ecosystem.config.js

Read more about application declaration here

#Setup startup script

Restarting PM2 with the processes you manage on server boot/reboot is critical. To solve this, just run this command to generate an active startup script

$ pm2 save

Read more about startup script generator here

#Restart application on changes

It’s pretty easy with the --watch option

$ cd /path/to/my/app
$ pm2 start env.js --watch --ignore-watch="node_modules"

This will watch & restart the app on any file change from the current directory + all subfolders and it will ignore any changes in the node_modules folder --ignore-watch="node_modules".

You can then use pm2 logs to check for restarted app logs.

#CheatSheet

Here are some commands that are worth knowing. Just try them with a sample application or with your current web application on your development machine

Fork mode

$ pm2 start app.js --name my-api # Name process

Cluster mode

$ pm2 start app.js -i 0        # Will start maximum processes with LB depending on available CPUs
$ pm2 start app.js -i max      # Same as above, but deprecated.
$ pm2 scale app +3             # Scales `app` up by 3 workers
$ pm2 scale app 2              # Scales `app` up or down to 2 workers total

Listing

$ pm2 list               # Display all processes status
$ pm2 jlist              # Print process list in raw JSON
$ pm2 prettylist         # Print process list in beautified JSON

$ pm2 describe 0         # Display all information about a specific process

$ pm2 monit              # Monitor all processes

Logs

$ pm2 logs [--raw]       # Display all processes logs in streaming
$ pm2 flush              # Empty all log files
$ pm2 reloadLogs         # Reload all logs

Actions

$ pm2 stop all           # Stop all processes
$ pm2 restart all        # Restart all processes

$ pm2 reload all         # Will 0s downtime reload (for NETWORKED apps)

$ pm2 stop 0             # Stop specific process id
$ pm2 restart 0          # Restart specific process id

$ pm2 delete 0           # Will remove process from pm2 list
$ pm2 delete all         # Will remove all processes from pm2 list

Misc

$ pm2 reset <process>    # Reset meta data (restarted time...)
$ pm2 updatePM2          # Update in memory pm2
$ pm2 ping               # Ensure pm2 daemon has been launched
$ pm2 sendSignal SIGUSR2 my-app # Send system signal to script
$ pm2 start app.js --no-daemon
$ pm2 start app.js --no-vizion
$ pm2 start app.js --no-autorestart

#Updating PM2

We made it simple, there is no breaking change between releases and the procedure is straightforward

$ npm install pm2@latest -g

Then update the in-memory PM2

$ pm2 update

#Also see