How do you implement a configuration management system in Node.js?

Question

Accepted Answer

**Configuration management** — manage app settings across environments.

```javascript
// config.js
const Joi = require("joi");

const envSchema = Joi.object({
    NODE_ENV: Joi.string().valid("development", "production", "test").required(),
    PORT: Joi.number().default(3000),
    DATABASE_URL: Joi.string().uri().required(),
    REDIS_URL: Joi.string().uri().required(),
    JWT_SECRET: Joi.string().min(32).required(),
    SMTP_HOST: Joi.string().required(),
    SMTP_PORT: Joi.number().default(587),
}).unknown();

const { error, value: envVars } = envSchema.validate(process.env, {
    abortEarly: false,
});

if (error) {
    throw new Error(`Config validation error: ${error.message}`);
}

const config = {
    env: envVars.NODE_ENV,
    port: envVars.PORT,
    db: {
        url: envVars.DATABASE_URL,
    },
    redis: {
        url: envVars.REDIS_URL,
    },
    jwt: {
        secret: envVars.JWT_SECRET,
    },
    smtp: {
        host: envVars.SMTP_HOST,
        port: envVars.SMTP_PORT,
    },
};

module.exports = config;

// Usage
const config = require("./config");
app.listen(config.port);
const db = new Pool({ connectionString: config.db.url });
```

Node.js: How do you implement a configuration management system in Node.js?