1---
2title: Use ConfigModule for Environment Configuration
3impact: LOW-MEDIUM
4impactDescription: Proper configuration prevents deployment failures
5tags: devops, configuration, environment, validation
6---
7 
8## Use ConfigModule for Environment Configuration
9 
10Use `@nestjs/config` for environment-based configuration. Validate configuration at startup to fail fast on misconfigurations. Use namespaced configuration for organization and type safety.
11 
12**Incorrect (accessing process.env directly):**
13 
14```typescript
15// Access process.env directly
16@Injectable()
17export class DatabaseService {
18  constructor() {
19    // No validation, can fail at runtime
20    this.connection = new Pool({
21      host: process.env.DB_HOST,
22      port: parseInt(process.env.DB_PORT), // NaN if missing
23      password: process.env.DB_PASSWORD, // undefined if missing
24    });
25  }
26}
27 
28// Scattered env access
29@Injectable()
30export class EmailService {
31  sendEmail() {
32    // Different services access env differently
33    const apiKey = process.env.SENDGRID_API_KEY || 'default';
34    // Typos go unnoticed: process.env.SENDGRID_API_KY
35  }
36}
37```
38 
39**Correct (use @nestjs/config with validation):**
40 
41```typescript
42// Setup validated configuration
43import { ConfigModule, ConfigService, registerAs } from '@nestjs/config';
44import * as Joi from 'joi';
45 
46// config/database.config.ts
47export const databaseConfig = registerAs('database', () => ({
48  host: process.env.DB_HOST,
49  port: parseInt(process.env.DB_PORT, 10),
50  username: process.env.DB_USERNAME,
51  password: process.env.DB_PASSWORD,
52  database: process.env.DB_NAME,
53}));
54 
55// config/app.config.ts
56export const appConfig = registerAs('app', () => ({
57  port: parseInt(process.env.PORT, 10) || 3000,
58  environment: process.env.NODE_ENV || 'development',
59  apiPrefix: process.env.API_PREFIX || 'api',
60}));
61 
62// config/validation.schema.ts
63export const validationSchema = Joi.object({
64  NODE_ENV: Joi.string()
65    .valid('development', 'production', 'test')
66    .default('development'),
67  PORT: Joi.number().default(3000),
68  DB_HOST: Joi.string().required(),
69  DB_PORT: Joi.number().default(5432),
70  DB_USERNAME: Joi.string().required(),
71  DB_PASSWORD: Joi.string().required(),
72  DB_NAME: Joi.string().required(),
73  JWT_SECRET: Joi.string().min(32).required(),
74  REDIS_URL: Joi.string().uri().required(),
75});
76 
77// app.module.ts
78@Module({
79  imports: [
80    ConfigModule.forRoot({
81      isGlobal: true, // Available everywhere without importing
82      load: [databaseConfig, appConfig],
83      validationSchema,
84      validationOptions: {
85        abortEarly: true, // Stop on first error
86        allowUnknown: true, // Allow other env vars
87      },
88    }),
89    TypeOrmModule.forRootAsync({
90      inject: [ConfigService],
91      useFactory: (config: ConfigService) => ({
92        type: 'postgres',
93        host: config.get('database.host'),
94        port: config.get('database.port'),
95        username: config.get('database.username'),
96        password: config.get('database.password'),
97        database: config.get('database.database'),
98        autoLoadEntities: true,
99      }),
100    }),
101  ],
102})
103export class AppModule {}
104 
105// Type-safe configuration access
106export interface AppConfig {
107  port: number;
108  environment: 'development' | 'production' | 'test';
109  apiPrefix: string;
110}
111 
112export interface DatabaseConfig {
113  host: string;
114  port: number;
115  username: string;
116  password: string;
117  database: string;
118}
119 
120// Type-safe access
121@Injectable()
122export class AppService {
123  constructor(private config: ConfigService) {}
124 
125  getPort(): number {
126    // Type-safe with generic
127    return this.config.get<number>('app.port');
128  }
129 
130  getDatabaseConfig(): DatabaseConfig {
131    return this.config.get<DatabaseConfig>('database');
132  }
133}
134 
135// Inject namespaced config directly
136@Injectable()
137export class DatabaseService {
138  constructor(
139    @Inject(databaseConfig.KEY)
140    private dbConfig: ConfigType<typeof databaseConfig>,
141  ) {
142    // Full type inference!
143    const host = this.dbConfig.host; // string
144    const port = this.dbConfig.port; // number
145  }
146}
147 
148// Environment files support
149ConfigModule.forRoot({
150  envFilePath: [
151    `.env.${process.env.NODE_ENV}.local`,
152    `.env.${process.env.NODE_ENV}`,
153    '.env.local',
154    '.env',
155  ],
156});
157 
158// .env.development
159// DB_HOST=localhost
160// DB_PORT=5432
161 
162// .env.production
163// DB_HOST=prod-db.example.com
164// DB_PORT=5432
165```
166 
167Reference: [NestJS Configuration](https://docs.nestjs.com/techniques/configuration)
168