Agent Skills: NestJS Configuration Standards

NestJS Configuration Standards

Priority: P1 (OPERATIONAL)

Environment configuration and validation patterns for NestJS applications.

Setup

1. Library: Use @nestjs/config.
2. Initialization: Import ConfigModule.forRoot({ isGlobal: true }) in AppModule.

Validation

• Mandatory: Validate environment variables at startup.
• Tool: Use joi or a custom validation class.
• Effect: The app must crash immediately if a required env var (e.g., DB_URL) is missing.

// app.module.ts
ConfigModule.forRoot({
  validationSchema: Joi.object({
    NODE_ENV: Joi.string()
      .valid('development', 'production')
      .default('development'),
    PORT: Joi.number().default(3000),
    DATABASE_URL: Joi.string().required(),
  }),
});

Usage

• Injection: Inject ConfigService to access values.
• Typing: Avoid magic strings. Use a type-safe getter helper or a dedicated configuration object/interface.
• Secrets: Never commit .env files. Add .env* to .gitignore.

⚠️ Adding New Variables

When adding a new environment variable to the application, you MUST update all of the following:

1. src/config/env.validation.ts: Add the class property with appropriate class-validator decorators.
2. .env.example: Add a placeholder value so other developers know about it.
3. .env.development / .env.test: Add the actual development values.
4. CI/CD Pipelines & Infrastructure: You MUST map the new variable in your deployment scripts (e.g., .github/workflows/*.yml, gitlab-ci.yml, Terraform, or Azure Pipelines). Most modern cloud platforms (Cloud Run, ECS, Kubernetes) require explicit mapping of secrets/env-vars into the container runtime. Failure to do this will cause the production deployment to crash or silently fail.

Anti-Patterns

• No unchecked env vars: Validate all required variables at startup; app must crash if missing.
• No committed secrets: Add .env* to .gitignore; load values via ConfigService only.
• No new vars without CI/CD update: Always update env.validation.ts, .env.example, and pipeline manifests.