SpringCloud----服务降级，熔断Hystrix和ribbon重试

三、服务降级

3.1 基于Ribbon的服务降级—Hystrix

3.1.1 添加Hystrix依赖

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>

3.1.2 在启动类中添加@EnableHystrix注解

@SpringBootApplication
@EnableDiscoveryClient
@EnableHystrix
public class GoodsUiApplication {

    public static void main(String[] args) {
        SpringApplication.run(GoodsUiApplication.class, args);
    }

}

3.1.3 在服务调用方法上添加@HystrixCommand注解

/**
 * 访问goods-provider服务的“goods/{id}”
 */
@HystrixCommand(fallbackMethod = "fallback_getGoods",commandProperties = {
    @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="1000")
})
public Goods getGoods(String goodsId){
    //2.接收对象数据类型的返回
    Goods goods = restTemplate.getForObject("http://goods-provider/goods/"+goodsId, Goods.class);
    return goods;
}

public Goods fallback_getGoods(String goodsId){
    //return new Goods("0","服务降级返回的商品",0.00);
    return null;
}

3.2 基于Feign的服务降级—Hystrix

　　Feign已经集成了Hystrix，但是需要配置

　　　　3.2.1 配置yml

　　

feign:
  hystrix:
    enabled: true

3.2.2 在服务调用方中配置降级服务

//服务的调用如果失败，则调用fallback指定的类中的同名方法
@FeignClient(value = "order-provider", fallback = OrderUIServiceFallback.class)
public interface OrderUIService {


    @RequestMapping(value = "order/list",method = RequestMethod.GET)
    public List<Order> listOrders(@RequestParam("pageNum") Integer pageNum,
                                  @RequestParam("pageSize") Integer pageSize);


    @RequestMapping(value = "order/add",method = RequestMethod.POST)
    public ResultVO doAdd(Order order);

    @RequestMapping(value = "order/add",method = RequestMethod.POST)
    public ResultVO test(@RequestBody Order order,
                         @RequestParam("pageNum") Integer num,
                         @RequestParam("pageSize") Integer size);


}

3.2.3 定义fallback类

@Component
public class OrderUIServiceFallback implements OrderUIService {

    @Override
    public List<Order> listOrders(Integer pageNum, Integer pageSize) {
        //降级服务
        return null;
    }

    @Override
    public ResultVO doAdd(Order order) {
        //降级服务
        return null;
    }

    @Override
    public ResultVO test(Order order, Integer num, Integer size) {
        //降级服务
        return null;
    }
}

3.2.4 设置超时时间

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 1000

3.3 在服务提供者配置服务降级—Hystrix

• 添加Hystrix依赖

• <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
  </dependency>

  在启动类添加@EnableHystrix注解

• @SpringBootApplication
  @EnableEurekaClient
  @EnableHystrix
  public class GoodsProviderApplication {
  
      public static void main(String[] args) {
          SpringApplication.run(GoodsProviderApplication.class, args);
      }
  
  }

• 在服务提供者上配置服务降级方案

• @RequestMapping(value = "/{id}" , method = RequestMethod.GET)
  @HystrixCommand(fallbackMethod = "fallback_get",commandProperties = {
      @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="1000")
  })
  public Goods get(@PathVariable("id") String gid){
      if(!"101".equals(gid)){
          try {
              Thread.sleep(3000);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
      }
      return new Goods(gid,"查询的商品",33.33);
  }
  
  public Goods fallback_get(@PathVariable("id") String gid){
      return new Goods("0","这是服务降级方案响应的商品信息",0.0);
  }

熔断器配置（服务熔断）

2.3.2 服务熔断实现

• 导入hystrix依赖

• 启动类添加@EnableHystrix或者@CircuitBreaker注解

2.3.4 服务提供者实现服务熔断

• 提供服务的方法

@RequestMapping(value = "/test",method = RequestMethod.GET)
//服务熔断配置
@HystrixCommand(fallbackMethod = "fallback_test",commandProperties = {
    @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="1000"),
    @HystrixProperty(name="circuitBreaker.enabled",value="true"),
    @HystrixProperty(name="circuitBreaker.sleepWindowInMilliseconds",value="10000"), //时间
    @HystrixProperty(name="circuitBreaker.requestVolumeThreshold",value="10"), //请求次数
    @HystrixProperty(name="circuitBreaker.errorThresholdPercentage",value="50"), //服务错误率
})
public String test(@RequestParam("num") Integer num){
    int n =  (int)Math.floor(Math.random()*100);
    int r = n/num;
    if(num>10){
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    return "服务正常返回的结果："+n+"/"+num+"="+r;
}

public String fallback_test(@RequestParam("num") Integer num){
    return "服务降级响应：num不能为0";
}

2.3.5 服务消费者实现服务熔断

• Ribbon调用服务的方法

  • Hystrix默认开启了熔断（熔断阈值是5s 20次还是10S 20次，不清楚），若需自定义配置则通过如下配置完成：

@HystrixCommand(fallbackMethod = "fallback_getGoods",commandProperties = {
    @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="100"),
    @HystrixProperty(name="circuitBreaker.enabled",value="true"),
    @HystrixProperty(name="circuitBreaker.sleepWindowInMilliseconds",value="10000"),//时间
    @HystrixProperty(name="circuitBreaker.requestVolumeThreshold",value="10"),   //请求次数
    @HystrixProperty(name="circuitBreaker.errorThresholdPercentage",value="50"), //服务错误率
})
public Goods getGoods(String goodsId){
    //2.接收对象数据类型的返回
    Goods goods = restTemplate.getForObject("http://goods-provider/goods/"+goodsId, Goods.class);
    return goods;
}

public Goods fallback_getGoods(String goodsId){
    return null;
}

Feign配置熔断器参数—application.yml

hystrix:
  command:
   default:
     execution:
       isolation:
         thread:
           timeoutInMilliseconds: 1000
     circuitBreaker:
       enabled: true
    ## ...

2.5 Ribbon的负载均衡和重试机制

2.5.1 Ribbon负载均衡

当服务提供者是集群部署时，服务消费者对服务提供者进行基于Ribbon的调用时，Ribbon是实现了负载均衡的

2.5.2 Ribbon的重试机制

当服务消费者通过Ribbon进行服务调用时，如果服务提供者第一次不能正常的响应，Ribbon可以重新发送(一次)请求

ribbon默认开始了重试机制，重试次数1次，其他节点2次，连接超时时间1s，请求响应等待时间1s

ribbon:
ConnectTimeout: 1000
ReadTimeout: 1000
OkToRetryOnAllOperations: true
MaxAutoRetries: 1
MaxAutoRetriesNextServer: 2

2.5.3 Feign的超时设置

• hystrix超时时间 与 ribbon超时时间的关系

• 

yml设置

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 5000
ribbon:
  ConnectTimeout: 3000
  ReadTimeout: 3000
  OkToRetryOnAllOperations: false