NestJS Config Module

Registering ConfigModule Globally

Import ConfigModule.forRoot({ isGlobal: true }) once in AppModule so ConfigService is available everywhere without re-importing. It loads .env by default and merges values into process.env.

ConfigModule.forRoot({
  isGlobal: true,
  envFilePath: ['.env.local', '.env'],
  validationSchema: Joi.object({
    NODE_ENV: Joi.string().valid('development', 'production', 'test').required(),
    PORT: Joi.number().default(3000),
    JWT_SECRET: Joi.string().min(16).required(),
  }),
})

A validation schema fails fast at boot when required variables are missing or invalid.

Reading Values With ConfigService

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

  get fromAddress() {
    return this.config.get<string>('MAIL_FROM');
  }
}

• config.get('KEY') reads an environment variable or custom config property.
• config.getOrThrow('KEY') throws if the key is missing.
• load factories can return nested config objects for namespacing.
• ignoreEnvFile: true is useful in production when the platform injects env vars.

ConfigModule Cheatsheet

Options and APIs you will use most.

Namespaced Configuration

Use registerAs to create database or jwt namespaces, then inject them with typed helpers for cleaner access than flat env keys everywhere.

export default registerAs('database', () => ({
  url: process.env.DATABASE_URL,
  ssl: process.env.DB_SSL === 'true',
}));

Feeding Other Modules

TypeORM, JWT, and Mail modules commonly use registerAsync factories that inject ConfigService to read secrets at runtime.

Common Mistakes

• Forgetting isGlobal: true and re-importing ConfigModule in every feature.
• Not validating env vars and discovering missing secrets only in production traffic.
• Committing a filled .env file with real credentials.
• Assuming .env files exist in container/prod environments where only real env vars are set.

Key Takeaways

• ConfigModule loads env files and exposes ConfigService for DI.
• Validate configuration at boot with a schema.
• Use namespaced registerAs factories for structured config.
• Wire other Nest modules via registerAsync + ConfigService.