java-microservices

Java Microservices Skill

Build production microservices with Spring Cloud and distributed system patterns.

Overview

This skill covers microservices architecture with Spring Cloud including service discovery, API gateway, circuit breakers, event-driven communication, and distributed tracing.

When to Use This Skill

Use when you need to:

• Design microservices architecture
• Implement service-to-service communication
• Configure resilience patterns
• Set up event-driven messaging
• Add distributed tracing

Topics Covered

Spring Cloud Components

• Config Server (centralized config)
• Service Discovery (Eureka, Consul)
• API Gateway (Spring Cloud Gateway)
• Load Balancing (Spring Cloud LoadBalancer)

Resilience Patterns

• Circuit Breaker (Resilience4j)
• Retry with backoff
• Bulkhead isolation
• Rate limiting

Event-Driven Architecture

• Apache Kafka integration
• Spring Cloud Stream
• Saga pattern
• Event sourcing basics

Observability

• Distributed tracing (Micrometer)
• Metrics (Prometheus)
• Log correlation

Quick Reference

// Saga with Choreography
@Component
public class OrderSagaListener {

    @KafkaListener(topics = "order.created")
    public void handleOrderCreated(OrderCreatedEvent event) {
        inventoryService.reserve(event.getItems());
    }

    @KafkaListener(topics = "payment.failed")
    public void handlePaymentFailed(PaymentFailedEvent event) {
        // Compensating transaction
        inventoryService.release(event.getOrderId());
        orderService.cancel(event.getOrderId());
    }
}

// Circuit Breaker Configuration
@Configuration
public class ResilienceConfig {

    @Bean
    public Customizer<Resilience4JCircuitBreakerFactory> cbCustomizer() {
        return factory -> factory.configureDefault(id ->
            new Resilience4JConfigBuilder(id)
                .circuitBreakerConfig(CircuitBreakerConfig.custom()
                    .failureRateThreshold(50)
                    .waitDurationInOpenState(Duration.ofSeconds(30))
                    .slidingWindowSize(10)
                    .build())
                .build());
    }
}

// API Gateway Routes
@Configuration
public class GatewayConfig {

    @Bean
    public RouteLocator routes(RouteLocatorBuilder builder) {
        return builder.routes()
            .route("orders", r -> r
                .path("/api/orders/**")
                .filters(f -> f
                    .stripPrefix(1)
                    .circuitBreaker(c -> c.setName("order-cb"))
                    .retry(retry -> retry.setRetries(3)))
                .uri("lb://order-service"))
            .build();
    }
}

Observability Configuration

management:
  tracing:
    sampling:
      probability: 1.0
  endpoints:
    web:
      exposure:
        include: health,info,metrics,prometheus

logging:
  pattern:
    level: "%5p [${spring.application.name:},%X{traceId:-},%X{spanId:-}]"

Common Patterns

Saga Pattern

Order → Inventory → Payment → (Success | Compensate)

Circuit Breaker States

CLOSED → (failures exceed threshold) → OPEN
OPEN → (wait duration) → HALF_OPEN
HALF_OPEN → (success) → CLOSED
HALF_OPEN → (failure) → OPEN

Troubleshooting

Common Issues

Problem	Cause	Solution
Cascade failure	No circuit breaker	Add Resilience4j
Message lost	No ack	Enable manual ack
Inconsistent data	No compensation	Implement saga
Service not found	Discovery delay	Tune heartbeat

Debug Checklist

□ Trace request (traceId)
□ Check circuit breaker state
□ Verify Kafka consumer lag
□ Review gateway routes
□ Monitor retry counts

Usage

Skill("java-microservices")

Related Skills

• java-spring-boot - Spring Cloud
• java-docker - Containerization