How do you manage configuration in NestJS?

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NestJS provides the **`@nestjs/config`** package for managing configuration and environment variables in a structured, type-safe, injectable way. It loads `.env` files, validates config, and makes values available throughout the app via the injectable `ConfigService`. ## Setting up ConfigModule ```ts import { ConfigModule } from "@nestjs/config"; @Module({ imports: [ ConfigModule.forRoot({ isGlobal: true, // available app-wide without re-importing envFilePath: ".env", validationSchema: Joi.object({ // validate env vars at startup (fail fast) DATABASE_URL: Joi.string().required(), PORT: Joi.number().default(3000), JWT_SECRET: Joi.string().required(), }), }), ], }) export class AppModule {} ``` `ConfigModule.forRoot()` loads environment variables (from `.env` + the process environment) and — crucially — can **validate** them with a schema (Joi), so a missing or invalid config crashes the app at startup with a clear error rather than failing mysteriously at runtime. ## Reading config via ConfigService (injectable) ```ts @Injectable() export class DatabaseService { constructor(private configService: ConfigService) {} // inject ConfigService connect() { const url = this.configService.get("DATABASE_URL"); const port = this.configService.get("PORT", 3000); // with a default } } ``` Instead of reading `process.env` directly everywhere, you inject `ConfigService` and call `get()` — type-safe, testable, and centralized. ## Namespaced/typed configuration ```ts // config/database.config.ts — group related config with registerAs export default registerAs("database", () => ({ host: process.env.DB_HOST, port: parseInt(process.env.DB_PORT, 10), })); // load it: ConfigModule.forRoot({ load: [databaseConfig] }) // access it: configService.get("database.host") ``` Namespacing groups related settings and keeps config organized as it grows. ## Why not just use process.env directly? ```text ✗ process.env scattered everywhere → hard to test, no validation, stringly-typed ✓ ConfigService → injectable (mockable in tests), validated at startup, typed, centralized — the structured NestJS way ``` ## Secrets and environments ```text ✓ Keep secrets in .env (GITIGNORED) — commit a .env.example documenting required vars ✓ In production, inject config via the platform's env vars / secret manager ✓ Validate at startup so misconfiguration fails immediately with a clear message ``` ## Why it matters Proper configuration management is essential for any real application — handling database URLs, API keys, ports, secrets, and feature flags safely and flexibly across environments (dev, staging, production). NestJS's `@nestjs/config` provides the structured, idiomatic way to do this, and understanding it is important everyday knowledge. The key advantages over reading `process.env` directly are significant: the injectable **`ConfigService`** makes config testable (mockable in tests) and centralized; **validation at startup** (with a Joi schema) catches missing or malformed configuration immediately with a clear error rather than as a confusing runtime failure deep in a request; and namespacing keeps growing config organized. Combined with the security best practice of keeping secrets in gitignored `.env` files (and a committed `.env.example`), this gives you safe, portable, validated configuration. Knowing how to set up `ConfigModule`, inject and use `ConfigService`, and validate config is fundamental for building production-ready NestJS applications and reflects professional back-end practice.