目录
1.概念
服务降级:服务器繁忙,请稍后再试,不让客户端等待,并立即返回一个友好的提示(一般发生在 程序异常,超时,服务熔断触发服务降级,线程池、信号量 打满也会导致服务降级)
服务熔断 : 达到最大服务访问后,直接拒绝访问,然后调用服务降级的方法并返回友好提示(如保险丝一样)
服务限流 : 秒杀等高并发操作,严禁一窝蜂的过来拥挤,排队进入,一秒钟N个,有序进行
***一.服务降级***
2.不使用Hystrix的项目
大致的Service和Controller层如下
***************Controller***************** package com.sky.springcloud.controller; import com.sky.springcloud.service.PaymentService; import lombok.extern.slf4j.Slf4j; import org.springframework.beans.factory.annotation.Value; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController; import javax.annotation.Resource; @RestController @Slf4j public class PaymentController { @Resource private PaymentService paymentService; @Value(\"${server.port}\") private String serverport; @GetMapping(\"/payment/hystrix/ok/{id}\") public String paymentInfo_Ok(@PathVariable(\"id\") Integer id){ String result = paymentService.paymentInfo_ok(id); log.info(\"*****\"+ result); return result; } @GetMapping(\"/payment/hystrix/timeout/{id}\") public String paymentInfo_TimeOut(@PathVariable(\"id\") Integer id){ String result = paymentService.payment_Info_TimeOut(id); } *******************Service******************** package com.sky.springcloud.service; import org.springframework.stereotype.Service; import java.util.concurrent.TimeUnit; @Service public class PaymentServiceImpl implements PaymentService{ @Override public String paymentInfo_ok(Integer id) { return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_Ok. id:\" + id + \"\\t\" + \"~~~~~\"; public String payment_Info_TimeOut(Integer id) { try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); } return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_TimeOut. id:\" + id + \"\\t\" + \"~~~~~\";
在这种情况时,当通过浏览器访问 TimeOut这个方法,会三秒后返回结果,而当访问 OK 这个方法时,会直接返回结果(但是这是在访问量很少的时候,一旦访问量过多,访问OK时也会出现延迟,这里可以使用Jmeter模拟两万个访问量,如下)
使用 Jmeter 模拟后,再去访问OK,会明显出现加载的效果
3. 使用Hystrix
在主启动类添加注解
@EnableHystrix
package com.sky.springcloud; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.netflix.eureka.EnableEurekaClient; import org.springframework.cloud.netflix.hystrix.EnableHystrix; @SpringBootApplication @EnableEurekaClient //启用Eureka @EnableHystrix //启用Hystrix public class Payment8001 { public static void main(String[] args) { SpringApplication.run(Payment8001.class,args); } }
在原有的基础上,在Service层加上如下注解
@HystrixCommand(fallbackMethod = \"payment_Info_TimeOutHandler\",//当服务降级时,调用payment_Info_TimeOutHandler方法 commandProperties = { @HystrixProperty(name = \"execution.isolation.thread.timeoutInMilliseconds\", value = \"3000\")//设置时间为3秒,超过三秒就为时间超限
*****************改后的Service******************* package com.sky.springcloud.service; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty; import org.springframework.stereotype.Service; import java.util.concurrent.TimeUnit; @Service public class PaymentServiceImpl implements PaymentService{ @Override public String paymentInfo_ok(Integer id) { return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_Ok. id:\" + id + \"\\t\" + \"~~~~~\"; } @HystrixCommand(fallbackMethod = \"payment_Info_TimeOutHandler\",commandProperties = { @HystrixProperty(name = \"execution.isolation.thread.timeoutInMilliseconds\",value = \"3000\") }) public String payment_Info_TimeOut(Integer id) { try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); } // int a = 10 / 0; return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_TimeOut. id:\" + id + \"\\t\" + \"~~~~~\"; } public String payment_Info_TimeOutHandler(Integer id){ return \"线程超时或异常 \" + Thread.currentThread().getName(); } }
如上Service所示,如果再次访问TimeOut需要等待五秒,但是Hystrix设置的超时时间为三秒,所以当三秒后没有结果就会服务降级,从而调用TimeOutHandler这个指定 的方法来执行(或者有程序出错等情况也会服务降级)
4. 全局的Hystrix配置
@DefaultProperties(defaultFallback = “Gloub_Test”)
package com.sky.springcloud.service; import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty; import org.springframework.stereotype.Service; @Service @DefaultProperties(defaultFallback = \"Gloub_Test\") public class PaymentServiceImpl implements PaymentService{ @Override @HystrixCommand public String paymentInfo_ok(Integer id) { int a = 10 / 0; return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_Ok. id:\" + id + \"\\t\" + \"~~~~~\"; } @HystrixCommand(fallbackMethod = \"payment_Info_TimeOutHandler\",commandProperties = { @HystrixProperty(name = \"execution.isolation.thread.timeoutInMilliseconds\",value = \"3000\") }) public String payment_Info_TimeOut(Integer id) { /* try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); }*/ return \"线程池:\" + Thread.currentThread().getName() + \"paymentInfo_TimeOut. id:\" + id + \"\\t\" + \"~~~~~\"; public String payment_Info_TimeOutHandler(Integer id){ return \"线程超时或异常 \" + Thread.currentThread().getName(); public String Gloub_Test(){ return \"走了全局的\"; }
如上Service所示,加了@HystrixCommand的方法里,
如果没指定fallbackMethod 就会默认去找全局的defaultFallback
这里 当paymentInfo_ok 方法出错时,会调用Gloub_Test方法
当payment_Info_TimeOut出错时,会调用payment_Info_TimeOutHandler方法
***二.服务熔断***
1.熔断机制概述
熔断机制是应对雪崩效应的一种微服务链路保护机制,当扇出链路的某个微服务出错不可用或者响应时间太长,会进行服务的降级,进而熔断该节点微服务的调用,快速返回错误的相应信息.当检测到该节点微服务调用相应正常后,恢复调用链路.
2.项目中使用
在上面的基础上,改写Service和Controller(添加以下代码)
//是否开启服务熔断(断路器) @HystrixProperty(name = \"circuitBreaker.enabled\",value = \"true\"), //服务请求的次数 @HystrixProperty(name = \"circuitBreaker.requestVolumeThreshold\",value = \"10\"), //时间的窗口期 @HystrixProperty(name = \"circuitBreaker.sleepWindowInMilliseconds\", value = \"10000\"), //当失败率达到多少后发生熔断 @HystrixProperty(name = \"circuitBreaker.errorThresholdPercentage\",value = \"60\"), ******************Service***************** @HystrixCommand(fallbackMethod = \"paymentCircuitBreaker_fallback\", commandProperties = { @HystrixProperty(name = \"circuitBreaker.enabled\",value = \"true\"), @HystrixProperty(name = \"circuitBreaker.requestVolumeThreshold\",value = \"10\"), @HystrixProperty(name = \"circuitBreaker.sleepWindowInMilliseconds\", value = \"10000\"), @HystrixProperty(name = \"circuitBreaker.errorThresholdPercentage\",value = \"60\"), }) public String PaymentCircuitBreaker(@PathVariable(\"id\") Integer id){ if(id<0){ throw new RuntimeException(\"********** id不能为负\"); } String serialNumber = IdUtil.simpleUUID(); return Thread.currentThread().getName() + \"\\t\" + serialNumber; } public String paymentCircuitBreaker_fallback(@PathVariable(\"id\") Integer id){ return \"id 不能为负:\" + id; ************Controller******************** @GetMapping(\"/payment/circuit/{id}\") String result = paymentService.PaymentCircuitBreaker(id); log.info(result + \"***********\"); return result;
如上所示,当访问paymentCircuitBreaker时,如果id小于零则会有一个运行错误,这时候就会通过服务降级来调用paymentCircuitBreaker_fallback方法,当错误的次数达到60%的时候(自己设的),就会出现服务熔断,这个时候再访问id大于零的情况,也会发生服务降级,因为开起了服务熔断,需要慢慢的恢复正常.
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