Configuration via ConfigModule, not `process.env`

Inject ConfigService — services never read `process.env` directly.

NestJS·NestJS Modules·Medium·Since 2026-05-01

nestjs-config-module-not-process-env

Why it matters

Failure modes if this rule is ignored

Stake	If ignored
Hard to test	A service that reads process.env directly is not testable — you can't fake configuration.
Drops connection	Validation at boot means the app won't start if a var is missing.

How to fix

NestJS provides @nestjs/config with schema validation. Use it. Services receive an injected ConfigService — they don't read process.env directly. (This is the NestJS expression of rule 16.)

Examples

Bad

@Injectable()
export class LlmService {
  private client = new LlmClient({
    apiKey: process.env.LLM_API_KEY!,   // ← if missing, runtime crash
  });
}

Good

// apps/api/src/config/config.schema.ts
import { z } from 'zod';

export const ConfigSchema = z.object({
  LLM_API_KEY:   z.string().min(1),
  DATABASE_URL:  z.string().url(),
  PORT:          z.coerce.number().default(3000),
});

// apps/api/src/main.ts
ConfigModule.forRoot({
  validate: (env) => ConfigSchema.parse(env),
  isGlobal: true,
});

// libs/workspace/backend-feature/src/lib/llm.service.ts
@Injectable()
export class LlmService {
  private client: LlmClient;
  constructor(config: ConfigService) {
    this.client = new LlmClient({ apiKey: config.get('LLM_API_KEY') });
  }
}

Related principles

• Configuration is read at the entry point, not in the middle of the codeNxnx-monorepo-schema-config-at-entry

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