🛸 Introduction to Microservices

💡 What are Microservices?

Microservices are a software architectural style that structures an application as a collection of small, independent services. Each service is responsible for a specific business capability and can be developed, deployed, and scaled independently.

• Small, focused scope - each service does one thing well
• Independent deployment - services can be updated without affecting others
• Decentralized architecture - reduces single points of failure
• Technology agnostic - different services can use different technologies

💡 Why Use Microservices?

• Improved scalability - scale individual services as needed
• Faster development cycles - work on specific features without impacting the whole system
• Better fault isolation - failures in one service don't bring down the entire application
• Easier maintenance and updates

✅ Building Microservices with NestJS

NestJS provides first-class support for building microservices through its @nestjs/microservices module. This module simplifies creating lightweight, distributed systems that can communicate via various transport layers.

import { MicroserviceOptions } from '@nestjs/microservices';

const options: MicroserviceOptions = {
  transport: Transport.TCP,
};

💡 Understanding the ClientProxy

The ClientProxy is a crucial component in NestJS microservices architecture. It acts as a communication bridge between different services, enabling request-response and event-based messaging.

export class AuthService {
  constructor(
    @Inject('AUTH_SERVICE') private readonly client: ClientProxy,
  ) {}

  async login(payload: LoginPayload) {
    return this.client.send('login', payload).toPromise();
  }
}

💡 Message Patterns in Microservices

• RPC (Remote Procedure Call) - Synchronous request-response pattern
• Event-driven messaging - Asynchronous communication with events
• One-way messaging - Fire-and-forget pattern for commands

✅ Request/Response Messaging

In request/response messaging, a client sends a request to a service and waits for a response. This is useful for scenarios where immediate feedback is needed.

interface User {
  id: string;
  username: string;
  email: string;
}

// Service implementation
@MessagePattern('get-user')
async getUser(userId: string): Promise<User> {
  return await this.userService.findById(userId);
}

✅ Modular Decomposition

Microservices encourage modular decomposition, where the application is broken down into smaller, manageable modules. Each module can be developed and maintained independently.

• Each service has a clear responsibility
• Services communicate through well-defined APIs
• Independent deployment capabilities

💡 Handling Failures in Microservices

Microservice architectures must account for failure handling. Services should be designed to handle errors gracefully and continue operating even if some components fail.

• Implement circuit breakers to prevent cascading failures
• Use retry mechanisms for transient errors
• Design services to be idempotent where possible
• Monitor service health and performance

✅ Message Retry Mechanisms

When sending messages between services, it's important to handle potential failures. NestJS provides mechanisms for message retries to ensure reliability.

@CircuitBreaker(
  { 
    name: 'user-service',
    ttl: 5000,
    maxFailures: 3,
    resetTimeout: 10000
  }
)
@MessagePattern('create-user')
async createUser(userPayload: CreateUserDTO): Promise<User> {
  try {
    return await this.userService.create(userPayload);
  } catch (error) {
    throw new RpcException(error.message);
  }
}

✅ Best Practices for Microservices Development

• Keep services small and focused on a single responsibility
• Use lightweight, fast communication protocols
• Implement proper error handling and logging
• Ensure loose coupling between services
• Monitor service performance and health
• Follow domain-driven design principles

🔁 Event-Driven Architecture with Kafka/NATS

💡 Introduction to Event-Driven Architecture

Welcome to the world of real-time communication and microservices! Event-driven architecture (EDA) is a design pattern where components interact by producing, consuming, and reacting to events. This approach enables loosely coupled systems that can scale efficiently.

💡 Why Use Event-Driven Architecture?

• Enable real-time communication between services
• Decouple components for better scalability
• Handle high-throughput workloads efficiently
• Support complex event patterns like sagas and choreographies

💡 Message Brokers: Kafka vs NATS

Two popular choices for message brokers are Kafka and NATS. Kafka is ideal for high-throughput, persistent messaging with strong ordering guarantees. NATS offers a lighter-weight, in-memory solution with excellent performance and ease of use.

✅ Setting Up Producers and Consumers

// Kafka Producer Setup
const kafka = require('kafka-node');
const Client = kafka.Client;
const client = new Client('localhost:2181');
const producer = new kafka.Producer(client);

// NATS Producer Setup
const nats = require('nats').connect();
nats.publish('my-topic', JSON.stringify({ message: 'Hello World!' }));

// Kafka Consumer Setup
const consumer = new kafka.Consumer(client, [
  { topic: 'my-topic', partition: 0 }
]);

// NATS Consumer Setup
nats.subscribe('my-topic', function(msg) {
  console.log('Received message:', msg);
});

💡 Key Concepts in Event Handling

• Event schemas: Define the structure of your events
• Idempotency: Ensure safe event processing
• Retries and dead-letter queues: Handle failed messages
• Correlation IDs: Track related events across services

✅ Best Practices for Event-Driven Systems

• Use descriptive event names that reflect their purpose
• Keep events small and focused on a single domain
• Implement event versioning to maintain compatibility
• Monitor your system with tools like Kibana or NATS Monitoring

❌ Avoid Common Pitfalls

• Don't ignore error handling and retries
• Don't use events for synchronous operations
• Don't create tight coupling between services
• Don't forget to implement circuit breakers for resilience

💡 Real-World Applications of EDA

EDA is used in various scenarios like: E-commerce systems (order processing, inventory updates) Social media platforms (real-time notifications, feeds) IoT applications (device events, sensor data)