Sentinel

概念

分布式系统的流量防卫兵。随着微服务的流行，服务和服务之间的稳定性变得越来越重要。Sentinel 以流量为切入点，从流量控制、流量路由、熔断降级、系统自适应过载保护、热点流量防护等多个维度保护服务的稳定性。

特征

丰富的应用场景：Sentinel 承接了阿里巴巴近 10 年的双十一大促流量的核心场景，例如秒杀（即突发流量控制在系统容量可以承受的范围）、消息削峰填谷、集群流量控制、实时熔断下游不可用应用等。
完备的实时监控：Sentinel 同时提供实时的监控功能。您可以在控制台中看到接入应用的单台机器秒级数据，甚至 500 台以下规模的集群的汇总运行情况。
广泛的开源生态：Sentinel 提供开箱即用的与其它开源框架/库的整合模块，例如与 Spring Cloud、Apache Dubbo、gRPC、Quarkus 的整合。您只需要引入相应的依赖并进行简单的配置即可快速地接入 Sentinel。同时 Sentinel 提供 Java/Go/C++ 等多语言的原生实现。
完善的 SPI 扩展机制：Sentinel 提供简单易用、完善的 SPI 扩展接口。您可以通过实现扩展接口来快速地定制逻辑。例如定制规则管理、适配动态数据源等。

主要特征

开源生态

开启控制台

①在nacos-server/bin下双击startup.cmd

②在sentinel-dashboard下使用cmd输入：java -java sentinel-dashboard-1.6.3.jar

依据自己下载的版本而输入后面的jar包名称

在网页上输入localhost:8080/ 即可进入以下页面账号密码皆为sentinel

初始化工程

①构建模块导入依赖

<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
    <version>2.2.3.RELEASE</version>
</dependency>
<!--SpringCloud Alibaba Sentinel-datasource-nacos 持久化技术-->
<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-datasource-nacos</artifactId>
    <version>1.8.1</version>
</dependency>
<!--SpringCloud Alibaba Sentinel-->
<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
    <version>2.2.7.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
    <version>3.1.1</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</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

这里需要注意的是：如果自己的SpringBoot版本过低的话会报以下错误，我的Boot版本是2.2.6.RELEASE。

当然，如果SpringBoot版本过高会报以下错误：

2022-12-25 18:19:02.585 ERROR 7000 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'configurationPropertiesBeans' defined in class path resource [org/springframework/cloud/autoconfigure/ConfigurationPropertiesRebinderAutoConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [org.springframework.cloud.context.properties.ConfigurationPropertiesBeans] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:597) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:213) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.context.support.PostProcessorRegistrationDelegate.registerBeanPostProcessors(PostProcessorRegistrationDelegate.java:270) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.context.support.AbstractApplicationContext.registerBeanPostProcessors(AbstractApplicationContext.java:762) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:567) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:164) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.cloud.bootstrap.BootstrapApplicationListener.bootstrapServiceContext(BootstrapApplicationListener.java:212) ~[spring-cloud-context-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:117) ~[spring-cloud-context-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:74) ~[spring-cloud-context-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:85) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:66) ~[spring-boot-2.6.7.jar:2.6.7]
	at java.util.ArrayList.forEach(ArrayList.java:1257) ~[na:1.8.0_201]
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:120) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:114) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:65) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:339) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:297) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) [spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) [spring-boot-2.6.7.jar:2.6.7]
	at com.chf.CloudalibabaSentinalService8401.main(CloudalibabaSentinalService8401.java:11) [classes/:na]
Caused by: java.lang.IllegalStateException: Failed to introspect Class [org.springframework.cloud.context.properties.ConfigurationPropertiesBeans] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:485) ~[spring-core-5.3.19.jar:5.3.19]
	at org.springframework.util.ReflectionUtils.doWithLocalMethods(ReflectionUtils.java:321) ~[spring-core-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.buildLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:232) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.findLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:210) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(InitDestroyAnnotationBeanPostProcessor.java:149) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:305) ~[spring-context-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:1116) ~[spring-beans-5.3.19.jar:5.3.19]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.3.19.jar:5.3.19]
	... 30 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/springframework/boot/context/properties/ConfigurationBeanFactoryMetadata
	at java.lang.Class.getDeclaredMethods0(Native Method) ~[na:1.8.0_201]
	at java.lang.Class.privateGetDeclaredMethods(Class.java:2701) ~[na:1.8.0_201]
	at java.lang.Class.getDeclaredMethods(Class.java:1975) ~[na:1.8.0_201]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:467) ~[spring-core-5.3.19.jar:5.3.19]
	... 37 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.boot.context.properties.ConfigurationBeanFactoryMetadata
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[na:1.8.0_201]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_201]
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) ~[na:1.8.0_201]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_201]
	... 41 common frames omitted

这两点都是我在学习时遇到的问题，希望看到对于这篇文章的人能有所帮助。

②改application.yml

server:
  port: 8401
spring:
  application:
    name: cloud-sentinel-service
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848 #Nacos服务注册中心地址
    sentinel:
      transport:
        dashboard: localhost:8080 #配置 dashboard监控平台地址
        port: 8719 #默认8719端口 如果被占用就自增直至找到未被占用的端口

management:
  endpoint:
    sentinel:
      enabled: true
  endpoints:
    web:
      exposure:
        include: '*'

③改启动类只需在上面加个注解@EnableDiscoveryClient

@SpringBootApplication
@EnableDiscoveryClient //表明让注册中心清楚当前服务想被注册进去
public class CloudalibabaSentinalService {
    public static void main(String[] args) {
        SpringApplication.run(CloudalibabaSentinalService.class, args);
    }
}

④写控制层

@RestController
public class SentinelController {
    @Value("${server.port}")
    private String serverPort;

    @GetMapping("/test")
    public String test(){
        return "Sentinel test server_port：" + serverPort;
    }
}

⑤测试。即启动当前类。由于Sentinel是懒加载机制，所以需要先测试我们的控制层，这样页面才能显示到我们的服务。可以多运行几次这个方法即多刷新这个页面