260223:1415 20260223 nextJS & nestJS Best pratices

.agents/skills/nestjs-best-practices/rules/devops-use-config-module.md

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+---
+title: Use ConfigModule for Environment Configuration
+impact: LOW-MEDIUM
+impactDescription: Proper configuration prevents deployment failures
+tags: devops, configuration, environment, validation
+---
+
+## Use ConfigModule for Environment Configuration
+
+Use `@nestjs/config` for environment-based configuration. Validate configuration at startup to fail fast on misconfigurations. Use namespaced configuration for organization and type safety.
+
+**Incorrect (accessing process.env directly):**
+
+```typescript
+// Access process.env directly
+@Injectable()
+export class DatabaseService {
+  constructor() {
+    // No validation, can fail at runtime
+    this.connection = new Pool({
+      host: process.env.DB_HOST,
+      port: parseInt(process.env.DB_PORT), // NaN if missing
+      password: process.env.DB_PASSWORD, // undefined if missing
+    });
+  }
+}
+
+// Scattered env access
+@Injectable()
+export class EmailService {
+  sendEmail() {
+    // Different services access env differently
+    const apiKey = process.env.SENDGRID_API_KEY || 'default';
+    // Typos go unnoticed: process.env.SENDGRID_API_KY
+  }
+}
+```
+
+**Correct (use @nestjs/config with validation):**
+
+```typescript
+// Setup validated configuration
+import { ConfigModule, ConfigService, registerAs } from '@nestjs/config';
+import * as Joi from 'joi';
+
+// config/database.config.ts
+export const databaseConfig = registerAs('database', () => ({
+  host: process.env.DB_HOST,
+  port: parseInt(process.env.DB_PORT, 10),
+  username: process.env.DB_USERNAME,
+  password: process.env.DB_PASSWORD,
+  database: process.env.DB_NAME,
+}));
+
+// config/app.config.ts
+export const appConfig = registerAs('app', () => ({
+  port: parseInt(process.env.PORT, 10) || 3000,
+  environment: process.env.NODE_ENV || 'development',
+  apiPrefix: process.env.API_PREFIX || 'api',
+}));
+
+// config/validation.schema.ts
+export const validationSchema = Joi.object({
+  NODE_ENV: Joi.string()
+    .valid('development', 'production', 'test')
+    .default('development'),
+  PORT: Joi.number().default(3000),
+  DB_HOST: Joi.string().required(),
+  DB_PORT: Joi.number().default(5432),
+  DB_USERNAME: Joi.string().required(),
+  DB_PASSWORD: Joi.string().required(),
+  DB_NAME: Joi.string().required(),
+  JWT_SECRET: Joi.string().min(32).required(),
+  REDIS_URL: Joi.string().uri().required(),
+});
+
+// app.module.ts
+@Module({
+  imports: [
+    ConfigModule.forRoot({
+      isGlobal: true, // Available everywhere without importing
+      load: [databaseConfig, appConfig],
+      validationSchema,
+      validationOptions: {
+        abortEarly: true, // Stop on first error
+        allowUnknown: true, // Allow other env vars
+      },
+    }),
+    TypeOrmModule.forRootAsync({
+      inject: [ConfigService],
+      useFactory: (config: ConfigService) => ({
+        type: 'postgres',
+        host: config.get('database.host'),
+        port: config.get('database.port'),
+        username: config.get('database.username'),
+        password: config.get('database.password'),
+        database: config.get('database.database'),
+        autoLoadEntities: true,
+      }),
+    }),
+  ],
+})
+export class AppModule {}
+
+// Type-safe configuration access
+export interface AppConfig {
+  port: number;
+  environment: 'development' | 'production' | 'test';
+  apiPrefix: string;
+}
+
+export interface DatabaseConfig {
+  host: string;
+  port: number;
+  username: string;
+  password: string;
+  database: string;
+}
+
+// Type-safe access
+@Injectable()
+export class AppService {
+  constructor(private config: ConfigService) {}
+
+  getPort(): number {
+    // Type-safe with generic
+    return this.config.get<number>('app.port');
+  }
+
+  getDatabaseConfig(): DatabaseConfig {
+    return this.config.get<DatabaseConfig>('database');
+  }
+}
+
+// Inject namespaced config directly
+@Injectable()
+export class DatabaseService {
+  constructor(
+    @Inject(databaseConfig.KEY)
+    private dbConfig: ConfigType<typeof databaseConfig>,
+  ) {
+    // Full type inference!
+    const host = this.dbConfig.host; // string
+    const port = this.dbConfig.port; // number
+  }
+}
+
+// Environment files support
+ConfigModule.forRoot({
+  envFilePath: [
+    `.env.${process.env.NODE_ENV}.local`,
+    `.env.${process.env.NODE_ENV}`,
+    '.env.local',
+    '.env',
+  ],
+});
+
+// .env.development
+// DB_HOST=localhost
+// DB_PORT=5432
+
+// .env.production
+// DB_HOST=prod-db.example.com
+// DB_PORT=5432
+```
+
+Reference: [NestJS Configuration](https://docs.nestjs.com/techniques/configuration)