NestJS Environment Configuration

Simple environment setup using NestJS built-in features - no custom code needed.

🎯 How It Works

NestJS automatically loads environment files based on NODE_ENV:

NODE_ENV	File Loaded	When
(not set)	`.env`	Default (Production)
`development`	`.env.development`	Development
`uat`	`.env.uat`	UAT
`production`	`.env`	Production

📁 File Structure

backend/
├── .env                 # Production (default)
├── .env.development     # Development
├── .env.uat            # UAT
└── src/app.module.ts

📄 Environment Files

# .env (production - default)
DATABASE_URL=postgresql://user:pass@prod-db:5432/myapp
PORT=3000

# .env.development
DATABASE_URL=postgresql://user:pass@localhost:5432/myapp_dev
PORT=3000

# .env.uat
DATABASE_URL=postgresql://user:pass@uat-db:5432/myapp_uat
PORT=3000

⚙️ App Module Setup

// src/app.module.ts
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      envFilePath: [
        `.env.${process.env.NODE_ENV}`,
        '.env'
      ],
    }),
  ],
})
export class AppModule {}

📝 Package.json Scripts

{
  "scripts": {
    "start": "nest start",
    "start:dev": "NODE_ENV=development nest start --watch",
    "start:uat": "NODE_ENV=uat nest start",
    "start:prod": "NODE_ENV=production node dist/main",
    "build": "nest build"
  }
}

🎮 Usage in Code

// In any controller or service
import { Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

@Injectable()
export class AppService {
  constructor(private config: ConfigService) {}

  getDatabaseUrl(): string {
    return this.config.get('DATABASE_URL');
  }

  getPort(): number {
    return this.config.get('PORT');
  }
}

🚀 Commands

# Development
npm run start:dev
# Loads: .env.development

# UAT
npm run start:uat
# Loads: .env.uat

# Production
npm run start:prod
# Loads: .env

# Default (same as production)
npm start
# Loads: .env

🔍 Check Environment

// In main.ts or any file
console.log('NODE_ENV:', process.env.NODE_ENV || 'default');
console.log('Database:', process.env.DATABASE_URL);

// In controller
@Get('health')
getHealth() {
  return {
    environment: process.env.NODE_ENV || 'default',
    database: this.config.get('DATABASE_URL')
  };
}

✅ Default Behavior

Important: If you don't set NODE_ENV, NestJS uses .env file (production).

# These commands do the same thing:
npm start                    # Uses .env (default)
NODE_ENV=production npm start # Uses .env (explicit)

🐳 Docker

# Dockerfile
FROM node:18-alpine

ARG NODE_ENV=production
ENV NODE_ENV=${NODE_ENV}

WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

COPY . .
RUN npm run build

EXPOSE 3000
CMD ["npm", "run", "start:prod"]

# Build for different environments
docker build -t myapp:dev --build-arg NODE_ENV=development .
docker build -t myapp:uat --build-arg NODE_ENV=uat .
docker build -t myapp:prod .  # Uses production by default

🛠️ Best Practices

Use .env for production (default behavior)
Set NODE_ENV in scripts for other environments
Use ConfigService to access environment variables
Check console output to verify which environment is loaded
Never commit sensitive data - use .env.local for secrets

🚨 Troubleshooting

Problem	Solution
Variables not loading	Check file name: `.env.development` not `.env.dev`
Wrong environment	Check `NODE_ENV` value in console
Missing variables	Verify variable exists in correct env file
Default not working	Remember: no `NODE_ENV` = `.env` file