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Microservices with Spring Cloud

January 5, 2024

Microservices with Spring Cloud

Spring Cloud provides tools for developers to quickly build some of the common patterns in distributed systems. This guide explores key components and patterns in microservices architecture.

Service Discovery

Using Netflix Eureka:

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

Configuration Server

Centralized configuration:

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

Circuit Breaker

Using Resilience4j:

@CircuitBreaker(name = "userService", fallbackMethod = "fallbackMethod")
public User getUser(String userId) {
    return userServiceClient.getUser(userId);
}

public User fallbackMethod(String userId, Exception ex) {
    return new User("default", "Fallback User");
}

API Gateway

Using Spring Cloud Gateway:

@SpringBootApplication
@EnableDiscoveryClient
public class GatewayApplication {
    @Bean
    public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
        return builder.routes()
            .route("user_service", r -> r.path("/users/**")
                .uri("lb://user-service"))
            .route("order_service", r -> r.path("/orders/**")
                .uri("lb://order-service"))
            .build();
    }
}

Distributed Tracing

Using Spring Cloud Sleuth with Zipkin:

@SpringBootApplication
@EnableDiscoveryClient
public class ServiceApplication {
    @Bean
    public Sampler defaultSampler() {
        return Sampler.ALWAYS_SAMPLE;
    }
}

Event-Driven Architecture

Using Spring Cloud Stream:

@Service
public class OrderProcessor {
    @StreamListener(Sink.INPUT)
    public void handleOrder(Order order) {
        // Process the order
    }
    
    @StreamListener(Sink.INPUT)
    @SendTo(Source.OUTPUT)
    public OrderConfirmation processOrder(Order order) {
        return new OrderConfirmation(order.getId());
    }
}

Security

OAuth2 and JWT with Spring Security:

@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {
    @Override
    public void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
            .antMatchers("/public/**").permitAll()
            .anyRequest().authenticated();
    }
}

Monitoring

Using Spring Boot Actuator:

@SpringBootApplication
public class Application {
    @Bean
    public HealthIndicator customHealthIndicator() {
        return new HealthIndicator() {
            @Override
            public Health health() {
                return Health.up()
                    .withDetail("customKey", "customValue")
                    .build();
            }
        };
    }
}

Best Practices

  1. Service Independence

    • Loose coupling
    • Independent deployment
    • Database per service

  2. Resilience

    • Circuit breakers
    • Fallbacks
    • Bulkheads

  3. Monitoring

    • Centralized logging
    • Distributed tracing
    • Health checks

  4. Security

    • API Gateway authentication
    • Service-to-service security
    • OAuth2/JWT

  5. Testing

    • Unit tests
    • Integration tests
    • Contract tests

Spring Cloud makes it easier to implement these patterns and build robust microservices architectures.

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