微服务基础

单体架构 vs 微服务的取舍

微服务不是银弹，也不是"更先进"的必然选择。在决定采用微服务架构前，需要认真评估成本与收益。

核心概念名词解释

Spring Cloud 核心组件全景

OpenFeign 声明式客户端

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-circuitbreaker-resilience4j</artifactId>
</dependency>

// 主启动类开启 Feign
@SpringBootApplication
@EnableFeignClients
public class OrderServiceApplication { ... }

// 定义 Feign 客户端接口
@FeignClient(
    name = "product-service",      // 注册中心的服务名
    fallback = ProductClientFallback.class  // 降级实现
)
public interface ProductClient {

    @GetMapping("/products/{id}")
    ProductDTO getProduct(@PathVariable Long id);

    @PostMapping("/products/{id}/decrease-stock")
    void decreaseStock(@PathVariable Long id,
                       @RequestBody StockDecreaseRequest req);
}

// 降级实现（熔断后返回默认数据）
@Component
public class ProductClientFallback implements ProductClient {

    @Override
    public ProductDTO getProduct(Long id) {
        // 降级：返回默认商品信息
        return ProductDTO.builder().id(id).name("商品暂时不可用").build();
    }

    @Override
    public void decreaseStock(Long id, StockDecreaseRequest req) {
        throw new ServiceUnavailableException("库存服务暂时不可用");
    }
}

Resilience4j 熔断器配置

resilience4j:
  circuitbreaker:
    instances:
      product-service:           # 针对 product-service 的熔断配置
        sliding-window-size: 10  # 滑动窗口大小（10次请求）
        failure-rate-threshold: 50  # 失败率 ≥ 50% 时熔断
        wait-duration-in-open-state: 10s  # 断开状态等待 10s
        permitted-number-of-calls-in-half-open-state: 3
        automatic-transition-from-open-to-half-open-enabled: true
  retry:
    instances:
      product-service:
        max-attempts: 3
        wait-duration: 500ms
        retry-exceptions:
          - java.net.ConnectException  # 只重试连接异常

Spring Cloud Gateway 路由配置

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service   # lb:// 使用负载均衡
          predicates:
            - Path=/api/users/**
          filters:
            - StripPrefix=1
            - name: RequestRateLimiter  # 限流过滤器
              args:
                redis-rate-limiter.replenishRate: 100   # 每秒 100 个令牌
                redis-rate-limiter.burstCapacity: 200

        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**
          filters:
            - name: CircuitBreaker
              args:
                name: order-service-cb
                fallbackUri: forward:/fallback/orders