How to Explicitly Set the Port for Your NextJS Production Application on Ubuntu

When running a Next.js application with PM2 on an Ubuntu server, setting the environment variable directly in the command line might not always work as expected due to the way PM2 manages processes. Here’s how you can make sure your application starts on a specific port:

Use PM2 Environment Configuration

The most reliable way to set environment-specific configurations with PM2 is to use an ecosystem configuration file. This method allows you to define various environment variables and more using a structured JSON or JavaScript format.

Step 1: Create an Ecosystem File

1. Create a file named ecosystem.config.js (or use a similar name) in your project directory.

2. Define your application and specify the environment variables like PORT:

   module.exports = {
     apps: [
       {
         name: 'your-app-name',
         script: 'npm',
         args: 'run start',
         env: {
           PORT: 4000
         }
       }
     ]
   };
   

Step 2: Start Your Application with PM2

Use the ecosystem file to start your application:

pm2 start ecosystem.config.js

This command will read the configuration from the file and start your Next.js application with the specified environment variables.

Alternative: Use a .env File and Load It

If you prefer to stick with using .env files or use a different way to manage configuration, ensure your .env file is being read properly in the context of the application start command. While not managed directly by PM2, here is a common approach:

1. Install dotenv package:

   You need to make sure your app can load environment variables from a .env file. Use the dotenv package if necessary:

   npm install dotenv
   

2. Load .env in Next.js scripts:

   Modify your package.json or wherever your Node.js startup logic is defined to load the .env configuration:

   For an example using a script:

   "scripts": {
     "start": "node -r dotenv/config server.js"
   }
   

   Then, start your application with PM2:

   pm2 start npm --name 'your-app-name' -- run start
   

Double-check that:

• Your ecosystem.config.js (or .env management) is correctly placed in the directory where you run the PM2 command.
• Your server listens on the specified port.
• There are no conflicts with other processes using the same port.

Using the ecosystem configuration is generally the most straightforward and maintainable approach when working with PM2 on a server such as Ubuntu.