SpringCloud学习笔记 - @SentinelResource的fallbackblockHandler配置详解 - sentinel

1. sentinel服务负载均衡测试

sentinel默认开启了负载均衡的轮询模式，为了测试sentinel服务负载均衡的效果，需要先创建两个服务提供者和一个服务消费者。

1.1. 分别创建两个服务提供者-支付服务9003、9004

1. 添加pom依赖： 提供者只需要将自己注册到服务注册中心即可，因此只需要添加spring-cloud-starter-alibaba-nacos-discovery。

	<dependencies><!--自定义api--><dependency><groupId>com.atguigu.springboot</groupId><artifactId>cloud-api-commons</artifactId><version>1.0-SNAPSHOT</version></dependency><!--nacos服务发现--><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><!--springboot web--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><!--日常通用jar包--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies>

2. 编写yaml配置文件： 注意给两个服务分配不同的端口9003、9004

server:port: 9003spring:application:name: nacos-payment-providercloud:nacos:discovery:server-addr: localhost:8848management:endpoints:web:exposure:include: "*"

3. 创建主启动类

@SpringBootApplication
@EnableDiscoveryClient
public class PaymentMain9003 {public static void main(String[] args) {SpringApplication.run(PaymentMain9003.class,args);}
}

4. 创建业务类

package com.atguigu.alibaba.controller;import com.atguigu.springcloud.entities.CommonResult;
import com.atguigu.springcloud.entities.Payment;
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 java.util.HashMap;/*** @author 强浩* @version 1.0.0* Copyright(c) YTANG All Rights Reserved* @className* @project 管理系统* @date 2022年09月14日*/
@RestController
@Slf4j
public class PaymentController {@Value("${server.port}")private String serverPort;//模拟数据库public static HashMap<Long, Payment> hashMap = new HashMap<>();static {hashMap.put(1L, new Payment(1L,"28a8c1e3bc2742d8848569891fb42181"));hashMap.put(2L,new Payment(2L,"bba8c1e3bc2742d8848569891ac32182"));hashMap.put(3L,new Payment(3L,"6ua8c1e3bc2742d8848569891xt92183"));}//传入id获取数据@GetMapping(value = "/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id){Payment payment = hashMap.get(id);CommonResult<Payment> commonResult = new CommonResult(200, "from mysql,serverPort:  " + serverPort, payment);return commonResult;}
}

2. 创建服务消费者-订单服务84

1. 添加pom依赖： 因为之后需要使用sentinel进行限流，所以需要添加sentinel的依赖

    <dependencies><dependency><groupId>com.atguigu.springboot</groupId><artifactId>cloud-api-commons</artifactId><version>1.0-SNAPSHOT</version></dependency><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-sentinel</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies>

2. 配置application.yaml文件：

server:port: 84spring:application:name: nacos-order-consumercloud:nacos:discovery:server-addr: localhost:8848sentinel:transport:dashboard: localhost:8080port: 8719server_url:payment_provider: http://nacos-payment-provider

3. 创建主启动类：

@SpringBootApplication
@EnableDiscoveryClient
public class OrderMain84 {public static void main(String[] args) {SpringApplication.run(OrderMain84.class,args);}
}

4. 创建RestTemplate服务调用配置类：

package com.atgugui.alibaba.config;import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;/*** @author 强浩* @version 1.0.0* Copyright(c) YTANG All Rights Reserved* @className* @project 管理系统* @date 2022年09月14日*/
@Configuration
public class ApplicationContextConfig {@Bean@LoadBalancedpublic RestTemplate getRestTemplate(){return new RestTemplate();}
}

5. 创建业务类： 注入RestTemplate进行远程服务调用

package com.atgugui.alibaba.controller;import com.atguigu.springcloud.entities.CommonResult;
import com.atguigu.springcloud.entities.Payment;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;import javax.annotation.Resource;/*** @author 强浩* @version 1.0.0* Copyright(c) YTANG All Rights Reserved* @className* @project 管理系统* @date 2022年09月14日*/
@RestController
@Slf4j
public class CircleBreakerController {public static final String SERVER_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@GetMapping("/consumer/fallback/{id}")public CommonResult<Payment> fallback(@PathVariable("id") Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVER_URL + "/paymentSQL/" + id, CommonResult.class, id);if(id == 4){throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if(result.getData() == null){throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}
}

5. 测试访问： 查看负载均衡的轮询效果
访问 http://localhost:84/consumer/fallback/1，多次访问，通过观察端口号可以发现，对支付服务进行了轮询访问。

2. fallback-业务错误处理

fallback只负责业务异常

1. 添加@SentinelResource注解，并配置fallback参数，指定服务降级处理方法

    @GetMapping("/consumer/fallback/{id}")@SentinelResource(value = "fallback", fallback = "handlerFallback")//指定fallback服务降级处理方法public CommonResult<Payment> fallback(@PathVariable("id") Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVER_URL + "/paymentSQL/" + id, CommonResult.class, id);if(id == 4){throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if(result.getData() == null){throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult<Payment> handlerFallback(@PathVariable Long id,Throwable e){Payment payment = new Payment(id,"null");return new CommonResult<>(444,"兜底异常handlerFallback,exception内容  "+e.getMessage(),payment);}

2. 测试： http://localhost:84/consumer/fallback/5，在没有降级处理的时候会直接报错，添加了fallback后进入降级处理方法。

3. blockHandler-限流规则处理

blockHandler处理违反了限流规则的请求

1. 给fallback方法资源添加限流规则

2. 配置@SentinelResource的blockHandler参数指定流控服务降级方法

    @GetMapping("/consumer/fallback/{id}")@SentinelResource(value = "fallback", blockHandler = "blockHandler")public CommonResult<Payment> fallback(@PathVariable("id") Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVER_URL + "/paymentSQL/" + id, CommonResult.class, id);if(id == 4){throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if(result.getData() == null){throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult<Payment> blockHandler(@PathVariable Long id, BlockException blockException){Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}

3. 测试：http://localhost:84/consumer/fallback/5

4. 服务熔断fallback和blockHandler同时配置

blockHandler和fallback 都进行了配置，则被限流降级而抛出BlockException时只会进入blockHandler处理逻辑。也就是说会优先处理服务限流，保证高可用，不要卡死服务器。

@RestController
@Slf4j
public class CircleBreakerController {public static final String SERVER_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@GetMapping("/consumer/fallback/{id}")@SentinelResource(value = "fallback", blockHandler = "blockHandler", fallback = "handlerFallback")public CommonResult<Payment> fallback(@PathVariable("id") Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVER_URL + "/paymentSQL/" + id, CommonResult.class, id);if(id == 4){throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if(result.getData() == null){throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult handlerFallback(@PathVariable  Long id,Throwable e) {Payment payment = new Payment(id,"null");return new CommonResult<>(444,"兜底异常handlerFallback,exception内容  "+e.getMessage(),payment);}public CommonResult<Payment> blockHandler(@PathVariable Long id, BlockException blockException){Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}
}

5. exceptionsToIgnore忽略指定异常

@RestController
@Slf4j
public class CircleBreakerController {public static final String SERVER_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@GetMapping("/consumer/fallback/{id}")@SentinelResource(value = "fallback", blockHandler = "blockHandler", fallback = "handlerFallback",exceptionsToIgnore = IllegalArgumentException.class)public CommonResult<Payment> fallback(@PathVariable("id") Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVER_URL + "/paymentSQL/" + id, CommonResult.class, id);if(id == 4){throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if(result.getData() == null){throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult handlerFallback(@PathVariable  Long id,Throwable e) {Payment payment = new Payment(id,"null");return new CommonResult<>(444,"兜底异常handlerFallback,exception内容  "+e.getMessage(),payment);}public CommonResult<Payment> blockHandler(@PathVariable Long id, BlockException blockException){Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}}

设置了忽略IllegalArgumentException异常，当出现该异常时不会进入降级逻辑。

6. sentinel整合openFeign实现服务熔断降级

一般在消费端添加feign组件实现服务降级：在84消费端添加openFeign的依赖，实现服务的熔断降级。

1. 引入openFeign的pom依赖： 这里因为版本冲突问题，需要将devtools组件取消掉，目前具体冲突原因还不知道。

<dependencies><dependency><groupId>com.atguigu.springboot</groupId><artifactId>cloud-api-commons</artifactId><version>1.0-SNAPSHOT</version></dependency><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><!--添加openFeign依赖--><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-alibaba-sentinel</artifactId><version>0.2.2.RELEASE</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><!--<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency>--><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies>

2. 修改yaml文件，添加fegin对sentinel的支持：

server:port: 84spring:application:name: nacos-order-consumercloud:nacos:discovery:server-addr: localhost:8848sentinel:transport:dashboard: localhost:8080port: 8719server_url:payment_provider: http://nacos-payment-providerfeign:sentinel:enabled: true

3. 在主启动类开启openFeign：

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class OrderMain84 {public static void main(String[] args) {SpringApplication.run(OrderMain84.class,args);}
}

4. 编写业务类： 使用@FeignClient注解，指定要进行访问的微服务名称，和发生熔断时所要调用的fallback方法

@FeignClient(value = "nacos-payment-provider",fallback = PaymentFallbackServiceImpl.class)
public interface PaymentService {@GetMapping(value = "/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id);
}

5. 服务降级方法实现类： 相当于给PaymentService增加了一个实现类，在发生熔断的情况下自动调用方法的fallback实现，来快速返回结果，防止系统卡死。

@Service
public class PaymentFallbackServiceImpl implements PaymentService {@Overridepublic CommonResult<Payment> paymentSQL(Long id) {return new CommonResult<>(44444,"服务降级返回,---PaymentFallbackService",new Payment(id,"errorSerial"));}
}

6. 现在就可以使用openFeign进行远程服务调用，我们只需要像之前一样将服务接口注入到controller层中，即可实现无感的远程服务调用了:

@RestController
@Slf4j
public class CircleBreakerController {//注入openFeign远程调用接口@Resourceprivate PaymentService paymentService;@GetMapping(value = "/consumer/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id){CommonResult<Payment> result = paymentService.paymentSQL(id);return result;}
}

7. 测试： 访问 http://localhost:84/consumer/paymentSQL/2，此时将9003服务提供者断开，84消费侧自动降级，不会被耗死。

7. 各熔断框架比较

	Sentinel	Hystrix	resilience4j
隔离策略	信号量隔离（并发线程数限流）	线程池隔商/信号量隔离	信号量隔离
熔断降级策略	基于响应时间、异常比率、异常数	基于异常比率	基于异常比率、响应时间
实时统计实现	滑动窗口（LeapArray）	滑动窗口（基于RxJava）	Ring Bit Buffer
动态规则配置	支持多种数据源	支持多种数据源	有限支持
拓展性	多个扩展点	插件的形式	接口的形式
基于注解的支持	支持	支持	支持
限流	基于QPS，支持基于调用关系的限流	有限的支持	Rate Limiter
流量整形	支持预热模式匀速器模式、预热排队模式	不支持	简单的Rate Limiter模式
系统自适应保护	支持	不支持	不支持
控制台	提供开箱即用的控制台，可配置规则、查看秒级监控，机器发观等	简单的监控查看	不提供控制台，可对接其它监控系统