STEP 10: BUILDING SCALABLE SYSTEMS — MESSAGE QUEUES & MICROSERVICES IN NODE.JS

Concept:

To scale beyond a monolith, modern Node.js backends often adopt microservices architecture, communicating via message queues (RabbitMQ, Kafka, Redis, NATS). This decouples services, increases fault tolerance, and allows horizontal scaling.

Key Concepts

Component	Role
Microservices	Independent, single-purpose services communicating over network
Message Queue	Buffers and dispatches messages asynchronously between services
Pub/Sub	Publisher emits events; subscribers react independently
API Gateway	Routes, authenticates, and aggregates APIs
Service Registry	Keeps track of active service instances

Real-World Use Case

You're building an e-commerce platform. Instead of a monolith:

Order Service handles placing orders
Inventory Service updates stock
Notification Service sends emails/SMS
Services communicate over RabbitMQ (event-based)

This allows:

Isolated deployments
Better load distribution
Async communication (no blocking)

Example with BullMQ (Redis-based Queue)

Producer

const { Queue } = require('bullmq');
const orderQueue = new Queue('orders');

await orderQueue.add('send-email', { to: '[email protected]', orderId: 123 });