MONOLITH EK SINGLE, LARGE codebase/deployment unit hai — SAARI functionality (orders, users, payments) EK JAGAH. Simple hai START karne ke liye, LEKIN scale karте-karте, EK CHHOTA CHANGE bhi POORE application ko REDEPLOY karvaता hai, aur TEAMS ek-doosre ke code se COLLIDE karte hain.

MICROSERVICES architecture mein, application ko SMALL, INDEPENDENT services mein TODA jaata hai (Order Service, User Service, Payment Service) — HAR EK apna khud ka DATABASE, DEPLOYMENT, aur SCALING rakhती hai. Services APAS mein REST (synchronous, IMMEDIATE response) ya MESSAGE QUEUES (Kafka/RabbitMQ, asynchronous, DECOUPLED) se COMMUNICATE karti hain.

// Order Service (independent deployment):
@SpringBootApplication
public class OrderServiceApplication { }

// Synchronous call — IMMEDIATE response chahiye:
Inventory inventory = restTemplate.getForObject(
    "http://inventory-service/api/check/" + productId, Inventory.class);

// Asynchronous — "fire and forget", DECOUPLED:
@Service
public class OrderService {
    private final KafkaTemplate<String, OrderEvent> kafkaTemplate;

    public void placeOrder(Order order) {
        orderRepository.save(order);
        kafkaTemplate.send("order-events", new OrderEvent(order));
        // Order service ko WAIT nahi karna — inventory/email services APNI SPEED se process karengi
    }
}