java-microservices

SKILL.md

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