壹、入围方案

Sentinel

• github地址：https://sentinelguard.io/zh-cn/docs/introduction.html
• 阿里出品，Spring Cloud Alibaba限流组件，目前持续更新中
• 自带Dashboard，可以查看接口Qps等，并且可以动态修改各种规则
• 流量控制，直接限流、冷启动、排队
• 熔断降级，限制并发限制数和相应时间
• 系统负载保护，提供系统级别防护，限制总体CPU等
• 主要核心：资源，规则（流量控制规则、熔断降级规则、系统保护规则、来源访问控制规则 和 热点参数规则。），和指标
• 文档非常清晰和详细，中文
• 支持动态规则（推模式和拉模式）
  

Hystrix

• github地址：https://github.com/Netflix/Hystrix/wiki
• Netflix出品，Spring Cloud Netflix限流组件，已经停止新特性开发，只进行bug修复，最近更新为2018年，功能稳定
• 有简单的dashboard页面
• 以隔离和熔断为主的容错机制，超时或被熔断的调用将会快速失败，并可以提供 fallback 机制的初代熔断框架，异常统计基于滑动窗口
  

resilience4j

• github地址：https://resilience4j.readme.io/docs
• 是一款轻量、简单，并且文档非常清晰、丰富的熔断工具。是Hystrix替代品，实现思路和Hystrix一致，目前持续更新中
• 需要自己对micrometer、prometheus以及Dropwizard metrics进行整合
• CircuitBreaker 熔断
• Bulkhead 隔离
• RateLimiter QPS限制
• Retry 重试
• TimeLimiter 超时限制
• Cache 缓存
  

自己实现(基于Guava)

• 基于Guava的令牌桶，可以轻松实现对QPS进行限流
  

贰、技术对比

叁、应用改造

3.1、sentinel

3.1.1、引入依赖

<dependency> <groupId>com.alibaba.cloud</groupId> <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId> <version>2.0.3.RELEASE</version></dependency>

3.1.2、改造接口或者service层

@SentinelResource(value = "allInfos",fallback = "errorReturn")

@Target({ElementType.METHOD, ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Inheritedpublic @interface SentinelResource { //资源名称 String value() default ""; //流量方向 EntryType entryType() default EntryType.OUT; //资源类型 int resourceType() default 0; //异常处理方法 String blockHandler() default ""; //异常处理类 Class<?>[] blockHandlerClass() default {}; //熔断方法 String fallback() default ""; //默认熔断方法 String defaultFallback() default ""; //熔断类 Class<?>[] fallbackClass() default {}; //统计异常 Class<? extends Throwable>[] exceptionsToTrace() default {Throwable.class}; //忽略异常 Class<? extends Throwable>[] exceptionsToIgnore() default {};}@RequestMapping("/get")@ResponseBody@SentinelResource(value = "allInfos",fallback = "errorReturn")public JsonResult allInfos(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num){ try { if (num % 2 == 0) { log.info("num % 2 == 0"); throw new BaseException("something bad with 2", 400); } return JsonResult.ok(); } catch (ProgramException e) { log.info("error"); return JsonResult.error("error"); } }

3.1.3、针对接口配置熔断方法或者限流方法

默认过滤拦截所有Controller接口

/** * 限流，参数需要和方法保持一致 * @param request * @param response * @param num * @return * @throws BlockException */ public JsonResult errorReturn(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num) throws BlockException { return JsonResult.error("error 限流" + num ); } /** * 熔断，参数需要和方法保持一直，并且需要添加BlockException异常 * @param request * @param response * @param num * @param b * @return * @throws BlockException */ public JsonResult errorReturn(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num,BlockException b) throws BlockException { return JsonResult.error("error 熔断" + num ); }

注意也可以不配置限流或者熔断方法。通过全局异常去捕获UndeclaredThrowableException或者BlockException避免大量的开发量

3.1.4、接入dashboard

spring: cloud: sentinel: transport: port: 8719 dashboard: localhost:8080

3.1.5、规则持久化和动态更新

接入配置中心如：zookeeper等等，并对规则采用推模式

3.2、hystrix

3.2.1、引入依赖

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId></dependency><dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId> <version>2.0.4.RELEASE</version></dependency><dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-hystrix</artifactId> <version>2.0.4.RELEASE</version></dependency>

3.2.2、改造接口

@HystrixCommand(fallbackMethod = "timeOutError")

@Target({ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)@Inherited@Documentedpublic @interface HystrixCommand { String groupKey() default ""; String commandKey() default ""; String threadPoolKey() default ""; String fallbackMethod() default ""; HystrixProperty[] commandProperties() default {}; HystrixProperty[] threadPoolProperties() default {}; Class<? extends Throwable>[] ignoreExceptions() default {}; ObservableExecutionMode observableExecutionMode() default ObservableExecutionMode.EAGER; HystrixException[] raiseHystrixExceptions() default {}; String defaultFallback() default "";}@RequestMapping("/get")@ResponseBody@HystrixCommand(fallbackMethod = "fallbackMethod")public JsonResult allInfos(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num){ try { if (num % 3 == 0) { log.info("num % 3 == 0"); throw new BaseException("something bad whitch 3", 400); } return JsonResult.ok(); } catch (ProgramException | InterruptedException exception) { log.info("error"); return JsonResult.error("error"); }}

3.2.3、针对接口配置熔断方法

/** * 该方法是熔断回调方法，参数需要和接口保持一致 * @param request * @param response * @param num * @return */public JsonResult fallbackMethod(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num) { response.setStatus(500); log.info("发生了熔断！！"); return JsonResult.error("熔断");}

3.2.4、配置默认策略

hystrix: command: default: execution: isolation: strategy: THREAD thread: # 线程超时15秒,调用Fallback方法 timeoutInMilliseconds: 15000 metrics: rollingStats: timeInMilliseconds: 15000 circuitBreaker: # 10秒内出现3个以上请求(已临近阀值),并且出错率在50%以上,开启断路器.断开服务,调用Fallback方法 requestVolumeThreshold: 3 sleepWindowInMilliseconds: 10000

3.2.5、接入监控

曲线：用来记录2分钟内流量的相对变化，我们可以通过它来观察到流量的上升和下降趋势。

集群监控需要用到注册中心

3.3、resilience4j

3.3.1、引入依赖

dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId></dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope></dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-spring-boot2</artifactId> <version>1.6.1</version></dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-bulkhead</artifactId> <version>1.6.1</version></dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-ratelimiter</artifactId> <version>1.6.1</version></dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-timelimiter</artifactId> <version>1.6.1</version></dependency>

可以按需要引入：bulkhead，ratelimiter，timelimiter等

3.3.2、改造接口

@RequestMapping("/get")@ResponseBody//@TimeLimiter(name = "BulkheadA",fallbackMethod = "fallbackMethod")@CircuitBreaker(name = "BulkheadA",fallbackMethod = "fallbackMethod")@Bulkhead(name = "BulkheadA",fallbackMethod = "fallbackMethod")public JsonResult allInfos(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num){ log.info("param----->" + num); try { //Thread.sleep(num); if (num % 2 == 0) { log.info("num % 2 == 0"); throw new BaseException("something bad with 2", 400); } if (num % 3 == 0) { log.info("num % 3 == 0"); throw new BaseException("something bad whitch 3", 400); } if (num % 5 == 0) { log.info("num % 5 == 0"); throw new ProgramException("something bad whitch 5", 400); } if (num % 7 == 0) { log.info("num % 7 == 0"); int res = 1 / 0; } return JsonResult.ok(); } catch (BufferUnderflowException e) { log.info("error"); return JsonResult.error("error"); }}

3.3.3、针对接口配置熔断方法

/** * 需要参数一致，并且加上相应异常 * @param request * @param response * @param num * @param exception * @return */public JsonResult fallbackMethod(HttpServletRequest request, HttpServletResponse response, @RequestParam Integer num, BulkheadFullException exception) { return JsonResult.error("error 熔断" + num );}

3.3.4、配置规则

resilience4j.circuitbreaker: instances: backendA: registerHealthIndicator: true slidingWindowSize: 100 backendB: registerHealthIndicator: true slidingWindowSize: 10 permittedNumberOfCallsInHalfOpenState: 3 slidingWindowType: TIME_BASED minimumNumberOfCalls: 20 waitDurationInOpenState: 50s failureRateThreshold: 50 eventConsumerBufferSize: 10 recordFailurePredicate: io.github.robwin.exception.RecordFailurePredicate resilience4j.retry: instances: backendA: maxRetryAttempts: 3 waitDuration: 10s enableExponentialBackoff: true exponentialBackoffMultiplier: 2 retryExceptions: - org.springframework.web.client.HttpServerErrorException - java.io.IOException ignoreExceptions: - io.github.robwin.exception.BusinessException backendB: maxRetryAttempts: 3 waitDuration: 10s retryExceptions: - org.springframework.web.client.HttpServerErrorException - java.io.IOException ignoreExceptions: - io.github.robwin.exception.BusinessException resilience4j.bulkhead: instances: backendA: maxConcurrentCalls: 10 backendB: maxWaitDuration: 10ms maxConcurrentCalls: 20 resilience4j.thread-pool-bulkhead: instances: backendC: maxThreadPoolSize: 1 coreThreadPoolSize: 1 queueCapacity: 1 resilience4j.ratelimiter: instances: backendA: limitForPeriod: 10 limitRefreshPeriod: 1s timeoutDuration: 0 registerHealthIndicator: true eventConsumerBufferSize: 100 backendB: limitForPeriod: 6 limitRefreshPeriod: 500ms timeoutDuration: 3s resilience4j.timelimiter: instances: backendA: timeoutDuration: 2s cancelRunningFuture: true backendB: timeoutDuration: 1s cancelRunningFuture: false

配置的规则可以被代码覆盖

3.3.5、配置监控

如grafana等

肆、关注点

• 是否需要过滤部分异常
• 是否需要全局默认规则
• 可能需要引入其他中间件
• k8s流量控制
• 规则存储和动态修改
• 接入改造代价
  

【后面的话】

个人建议的话，比较推荐sentinel，它提供了很多接口便于开发者自己拓展，同时我觉得他的规则动态更新也比较方便。最后是相关示例代码:单体应用示例代码

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