🏗️ Microservices Fundamentals

Technical Documentation for Principal Engineers

1. Overview and Problem Statement 🎯

Definition

Microservices architecture is a design approach where a single application is built as a suite of small, independent services, each running in its own process and communicating through well-defined APIs. Each service is built around specific business capabilities and can be independently deployed, scaled, and maintained.

Problems Solved

• Monolithic application complexity
• Scale and deployment challenges
• Development team coordination
• Technology stack limitations
• Long release cycles
• Single points of failure

Business Value

• Faster time to market
• Independent scaling
• Technology flexibility
• Better fault isolation
• Improved team autonomy
• Enhanced system maintainability

2. Detailed Solution/Architecture 📐

Core Concepts

2.1 Service Independence

• Single responsibility principle
• Independent deployment
• Decentralized data management
• Autonomous teams
• API contracts

2.2 Architecture Components

Key Components

1. API Gateway

   • Entry point for clients
   • Request routing
   • Protocol translation
   • Authentication/Authorization

2. Service Registry

   • Service discovery
   • Load balancing
   • Health monitoring

3. Config Server

   • Centralized configuration
   • Environment management
   • Secret management

3. Technical Implementation 💻

3.1 Basic Service Implementation

Spring Boot Example

@SpringBootApplication
@EnableDiscoveryClient
public class OrderServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(OrderServiceApplication.class, args);
    }
}

@RestController
@RequestMapping("/api/orders")
public class OrderController {
    private final OrderService orderService;
    
    @PostMapping
    public ResponseEntity<Order> createOrder(@RequestBody OrderRequest request) {
        Order order = orderService.createOrder(request);
        return ResponseEntity.ok(order);
    }
    
    @GetMapping("/{id}")
    public ResponseEntity<Order> getOrder(@PathVariable String id) {
        return orderService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }
}

Node.js Example

// app.js
const express = require('express');
const app = express();

class OrderService {
  async createOrder(orderData) {
    // Implementation
  }
  
  async getOrder(id) {
    // Implementation
  }
}

app.post('/api/orders', async (req, res) => {
  try {
    const order = await orderService.createOrder(req.body);
    res.json(order);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

app.listen(3000, () => console.log('Order service running on port 3000'));

3.2 Service Discovery Implementation

@Configuration
public class ServiceDiscoveryConfig {
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

@Service
public class OrderService {
    private final RestTemplate restTemplate;
    
    public OrderDetails getOrderWithPayment(String orderId) {
        Order order = findById(orderId);
        // Service discovery using logical service name
        Payment payment = restTemplate.getForObject(
            "http://payment-service/api/payments/{orderId}",
            Payment.class,
            orderId
        );
        return new OrderDetails(order, payment);
    }
}

4. Decision Criteria & Evaluation 📊

Service Boundaries Decision Matrix

Criterion	Monolithic	Microservices
Deployment	Simple	Complex
Scaling	Limited	Flexible
Development	Coupled	Independent
Testing	Simple	Complex
Resilience	Limited	High

When to Use Microservices

1. Large, complex applications
2. Different scaling requirements
3. Multiple development teams
4. Need for technology diversity
5. High availability requirements

5. Performance Metrics & Optimization ⚡

Key Metrics

• Service response time
• Transaction throughput
• Error rate
• Resource utilization
• API latency

Monitoring Implementation

@Configuration
public class MetricsConfig {
    @Bean
    public MeterRegistry meterRegistry() {
        return new SimpleMeterRegistry();
    }
}

@Service
public class MonitoredService {
    private final MeterRegistry registry;
    
    @Timed(value = "service.operation")
    public void performOperation() {
        registry.counter("operation.count").increment();
        // Operation implementation
    }
}

8. Anti-Patterns ⚠️

8.1 Chatty Services

❌ Wrong Implementation:

@Service
public class OrderService {
    private final RestTemplate restTemplate;
    
    public OrderDetails getOrderDetails(String orderId) {
        Order order = getOrder(orderId);
        // Multiple API calls for single operation
        Customer customer = getCustomer(order.getCustomerId());
        Payment payment = getPayment(orderId);
        Shipping shipping = getShipping(orderId);
        return new OrderDetails(order, customer, payment, shipping);
    }
}

✅ Correct Implementation:

@Service
public class OrderService {
    private final RestTemplate restTemplate;
    
    public OrderDetails getOrderDetails(String orderId) {
        // Single API call with composite response
        return restTemplate.getForObject(
            "http://order-aggregator-service/api/orders/{orderId}/details",
            OrderDetails.class,
            orderId
        );
    }
}

8.2 Shared Libraries

❌ Wrong:

// Shared domain objects across services
package com.company.shared.domain;

public class Order {
    private String id;
    private Customer customer;
    private Payment payment;
    // Shared domain logic
}

✅ Correct:

// Service-specific domain objects
package com.company.orderservice.domain;

public class Order {
    private String id;
    private String customerId;
    private String paymentId;
    // Service-specific logic
}

9. FAQ Section ❓

Q: How to handle service-to-service communication?

A: Options include:

1. Synchronous (REST, gRPC)
2. Asynchronous (Message Queues)
3. Event-driven architecture

Q: How to manage service discovery?

A: Use:

1. Service registry (Eureka, Consul)
2. DNS-based discovery
3. Load balancers

10. Best Practices & Guidelines 📚

10.1 Design Principles

1. Single Responsibility

   • One service per business capability
   • Clear boundaries
   • Independent data stores

2. API First

   • Define contracts early
   • Use API versioning
   • Implement backward compatibility

10.2 Security Implementation

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) {
        return http
            .oauth2ResourceServer()
            .jwt()
            .and()
            .authorizeRequests()
            .antMatchers("/api/public/**").permitAll()
            .anyRequest().authenticated()
            .and()
            .build();
    }
}

11. Troubleshooting Guide 🔧

Common Issues

1. Service Discovery Failures

   • Symptom: Services unable to find each other
   • Solution: Check registry health and network connectivity

2. Circuit Breaker Issues

   @CircuitBreaker(name = "orderService", fallbackMethod = "fallbackMethod")
   public Order getOrder(String orderId) {
       // Implementation
   }
   
   public Order fallbackMethod(String orderId, Exception ex) {
       // Fallback logic
   }

12. Testing Strategies 🧪

12.1 Testing Pyramid

1. Unit Tests

@Test
void whenCreateOrder_thenSuccess() {
    OrderRequest request = new OrderRequest("product1", 1);
    Order order = orderService.createOrder(request);
    assertNotNull(order);
    assertEquals("product1", order.getProductId());
}

2. Integration Tests

@SpringBootTest
class OrderServiceIntegrationTest {
    @Autowired
    private TestRestTemplate restTemplate;
    
    @Test
    void whenCallOrderAPI_thenSuccess() {
        ResponseEntity<Order> response = restTemplate.getForEntity(
            "/api/orders/{id}",
            Order.class,
            "order1"
        );
        assertEquals(HttpStatus.OK, response.getStatusCode());
    }
}

13. Real-world Use Cases 🌍

E-commerce Platform

• Product Catalog Service
• Order Management Service
• Payment Processing Service
• User Management Service
• Inventory Service

Implementation Example

@Service
public class OrderProcessingService {
    private final OrderRepository orderRepository;
    private final EventPublisher eventPublisher;
    
    @Transactional
    public Order processOrder(OrderRequest request) {
        // Create order
        Order order = orderRepository.save(new Order(request));
        
        // Publish event for other services
        eventPublisher.publish(new OrderCreatedEvent(order));
        
        return order;
    }
}

14. References and Additional Resources 📚

Books

• "Building Microservices" by Sam Newman
• "Microservices Patterns" by Chris Richardson

Articles

• Martin Fowler's Microservices Guide
• Netflix Tech Blog
• AWS Microservices Architecture

Documentation

• Spring Cloud
• Docker
• Kubernetes

For additional information and updates, refer to:

• Spring Cloud Documentation
• Microsoft Azure Microservices
• AWS Microservices