Sentinel流控和降级方案

Sentinel介绍

• 阿里巴巴中间件，负责流量控制和熔断降级。
• 适配Spring类框架
• 可原生开发

引入pom

<sentinel.version>1.7.1</sentinel.version>

<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-core</artifactId>
    <version>${sentinel.version}</version>
</dependency>
<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-annotation-aspectj</artifactId>
    <version>${sentinel.version}</version>
</dependency>
<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-transport-simple-http</artifactId>
    <version>${sentinel.version}</version>
</dependency>

• sentinel-core核心包
• sentinel-annotation-aspectj适合spring切面和注解

• sentinel-transport-simple-http便于接入console控制台

  SpringBoot配置

  @Configuration
  public class SentinelAspectConfiguration {
      @Bean
      public SentinelResourceAspect sentinelResourceAspect() {
          return new SentinelResourceAspect();
      }
  }

• 负责切面拦截

  @SentinelResource(value = "action")
  public boolean action(String str){
      return "Hi";
  }

• SentinelResource为Sentinel的注解

• value为资源标识

流控配置

@Data
@ToString
public static class Flow {
    private String resource;
    private int count;
    private int grade;
}

• Flow为自定义的配置文件
• resource为资源名称
• count为流控的阈值，线程数或QPS

• grade流控类型，0-线程，1-QPS

  /**
   * 刷新Flow
   */
  public synchronized void reloadFlow() {
      List<FlowRule> rules = new ArrayList<>(20);
  
      flows.forEach(e -> {
          if (StringUtils.isEmpty(e.getResource()) || e.getCount() == 0) {
              return;
          }
          log.warn(e.toString());
  
          FlowRule rule = new FlowRule();
          rule.setResource(e.getResource());
          //qps
          rule.setCount(e.getCount());
          rule.setGrade(e.getGrade());
          rules.add(rule);
      });
  
      if (rules.size() > 0) {
          FlowRuleManager.loadRules(rules);
          log.warn("Sentinel reloadFlow success!");
      }
  }

• 导入自定义的流控配置

  降级配置

  @Data
  @ToString
  public static class Degrade {
      private String resource;
      private int count;
      private int grade;
      private int window;
  }

• Degrade为自定义的降级配置文件

• resource为资源名称
• window为降级后持续的窗口时长，平均响应时间-秒、异常百分比-秒或异常数量-秒
• count为降级的参考指标，qps=5时的平均响应时间(最大为4.9s)、qps>=5时异常百分比或默认1分钟的异常数量

• grade降级类型，平均响应时间-0、异常百分比-1或异常数量-2

  /**
   * 刷新Degrade
   */
  public synchronized void reloadDegrade() {
      List<DegradeRule> rules = new ArrayList<>(20);
  
      degrades.forEach(e -> {
          if (StringUtils.isEmpty(e.getResource()) || e.getCount() == 0 || e.getWindow() == 0) {
              return;
          }
          log.warn(e.toString());
          DegradeRule rule = new DegradeRule();
          rule.setResource(e.getResource());
          //rt,ms
          rule.setCount(e.getCount());
          rule.setGrade(e.getGrade());
          //secs
          rule.setTimeWindow(e.getWindow());
          rules.add(rule);
      });
  
      if (rules.size() > 0) {
          DegradeRuleManager.loadRules(rules);
          log.warn("Sentinel reloadDegrade success!");
      }
  }

• 导入自定义的流控配置

• 慎重配置降级策略，若降级，影响范围是window时间内的请求都处于自动降级中

Fallback和BlockHandler

• Fallback，当异常时的处理策略，即有异常的容错方案；Fallback参数要和业务方法保持一致
• BlockHandler，被流控或降级时，指定窗口内的降级方案；BlockHandler参数要和业务方法保持一致，同时新增一个BlockException参数

Case

• 降级策略

  sentinel:
    flows[0]: #流控
      resource: action
      count: 1000 #number
      grade: 1 #thread-0,qps-1
    degrades[0]: # 降级
      resource: action
      window: 120 #rt-s,exceptionRatio-s,exceptionCount-s
      count: 100 #rt-art,exceptionRatio-[0.0,1.0],exceptionCount-number
      grade: 2 #RuleConstant:rt-0,exceptionRatio-1,exceptionCount/m-2

• 业务注解

  @SentinelResource(value = "action",fallback = "defaultFallback", blockHandler = "defaultBlockHandler")
  public boolean action(String str){
      return "Hi";
  }

public boolean defaultBlockHandler(String str, BlockException ex){
    return "Hi1";
}
public boolean defaultFallback(String str){
    return "Hi2";
}

控制台

• 下载源码启动即可
• 控制台可浏览和配置资源策略，基于内存
• 建议对接DB或Nacos
• 集群限流略微复杂，需要注意业务适配度及集群本身对应用的影响