How I use PM2 to run Node.js applications to production.

PM2 is a process manager for Node.js applications. It helps to monitor applications, their memory and CPU uses. Also, provides easy commands line to manipulate apps. In this article, I will explain to you how to deploy a Node.js application on a server using the pm2 tool.

Install PM2

PM2 depends on Node.js and python-software-properties, so we need to install them first:

sudo apt-get install python-software-properties
curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
sudo apt-get install nodejs

Then, we can install pm2 globally:

sudo npm i -g pm2

Create the config file

PM2 provides a command line for users to generate a config file. The config file will be generated in the YAML format under the project folder.

pm2 ecosystem # generates a config file

After generation, there is a file like:

apps:
  - script   : ./api.js
    name     : 'api-app'
    instances: 4
    exec_mode: cluster
    watch  : true
    env    :
      NODE_ENV: development
    env_production:
      NODE_ENV: production

Configuring PM2

Here are what some of the configuration options are for:

1. script: how to start the application. PM2 also supports starting Python applications.
2. instance: the number of instances you are going to create.
3. exec_mode: cluster/fork.
4. watch: if true, the application will auto-restart if any crash happened.
5. max_memory_restart: if true, PM2 will restart the application if the application exceeds the amount of memory.
6. env: all the env variables settings should be placed here.
7. error_file: a path string for forwarding stderr
8. out_file: a path string for forwarding stdout

Start!

Now use the following command to start the application. PM2 will read the configuration file, start applications and assign a unique id to the process.

pm2 start config.yml

PM2 provides a list function for showing all applications under PM2:

pm2 list

If you need to get more detailed info about one specific app, we can use the command:

pm2 show [app_id]

Thanks for reading, and I hope you guys learned something!