Environment Variables Management

Environment variables are special variables that can be set out of your Node.js applications, particularly useful to make your application configurable externally. Let’s say a cloud provider wants to change the listening port of your app or if you want to enable verbose logging without getting into the code.

CLI

Via CLI, the environment is conservative meaning that, when you will run different process management actions (restart, reload, stop/start), new environment variables will not be updated into your application.

Set environment

To set an environment variable via CLI:

$ ENV_VAR=value pm2 start app.js

Update environment

To update environment variables, you have to append the --update-env to the restart/reload command:

$ ENV_VAR=somethingnew pm2 restart app --update-env

Ecosystem process file

Any time you change the ecosystem process file, the environment variables will be updated.

Set Environment

To set default environment variables via ecosystem file, you just need to declare them under the “env:” attribute:

module.exports = {
  apps: [{
    name: "app",
    script: "./app.js",
    env: {
      NODE_ENV: "development"
    },
    env_test: {
      NODE_ENV: "test",
    },
    env_staging: {
      NODE_ENV: "staging",
    },
    env_production: {
      NODE_ENV: "production",
    }
  }]
}

Then start it:

$ pm2 start ecosystem.config.js

As you might have noticed, there is also a part about the env_test, env_staging and env_production in the ecosystem file.

For example to use the env_production variables instead of the default ones you just need to pass the --env <env_name> option:

$ pm2 start ecosystem.config.js --env production

Note: The env_production in the ecosystem file is a regex like env_* that can have any value and be called when using the CLI via -- env *.

Update

If you are using Ecosystem file to manage your application environment variables under the env: attribute, the updated ones will always be updated on pm2 <restart/reload> app.

$ pm2 restart/reload ecosystem.config.js [--env production]

Good practice: The NODE_ENV variable

A common convention in Node.js is that the NODE_ENV environment variable specifies the environment in which an application is running (usually, development or production).

For example, with express, setting NODE_ENV to “production” can improve performance by a factor of 3 according to the documentation. This enables:

• Cache for view templates.
• Cache for CSS files generated from CSS extensions.
• Generate less verbose error messages.