2021-12-19 周天 ## Hystrix介绍 Hystrix是由Netflix开源的一个延迟和容错库，用于隔离访问远程系统、服务或者第三方库，防止级联失败，从而提升系统的可用性与容错性。 ### Hystrix特性 Hystrix主要通过以下几点实现延迟和容错。 * 包裹请求 - `@HystrixCommand`注解（命令模式） * 跳闸机制 - 5秒内20次失败，一段时间内会停止访问服务 * 资源隔离 - 给每个服务提供小型线程池，线程池满立即拒绝请求 * 监控 * 回退机制 - 开发人员可提供默认回退逻辑 * 自我修复 - 一段时间内，会尝试调用一次服务，请求成功则关闭断路器 ## Hystrix 集成 ### 添加依赖 ``` xml <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-hystrix</artifactId> </dependency> ``` ### 开启断路器 在启动类上增加`@EnableHystrix`注解或者`@EnableCircuitBreaker`注解。 ### 直接使用`@HystrixCommand` ``` java @FeignClient(name = "mic-card",path = "/card/admin") public interface CardApi { @PostMapping("/count/home") @HystrixCommand ResultObject<CountVo> getHome(); } ``` ### 结合Feign使用 Feign默认是不启用Hystrix的，添加如下配置启用。 ``` yml feign: hystrix: enabled: true ``` ``` java /** * @Description card api服务 * @Date 2021-12-04 10:12 * @Created by mango */ @FeignClient(name = "mic-card",path = "/card/admin", configuration = {FeignConfiguration.class}, fallback = CardApiFallback.class) public interface CardApi { @GetMapping("/card/rand") ResultObject<CardVo> getRand(); @PostMapping("/count/home") ResultObject<CountVo> getHome(); } ## 回退机制，自定义实现回退逻辑 @Component @Slf4j class CardApiFallback implements CardApi { @Autowired private ResultUtil resultUtil; @Override public ResultObject<CardVo> getRand() { log.info("enter card api fallback"); CardVo cardVo = new CardVo(); cardVo.setName("enter fallback"); cardVo.setIsOpen("1"); cardVo.setCreateTime(DateUtil.now()); return resultUtil.success2obj(cardVo,"success"); } @Override public ResultObject<CountVo> getHome() { log.info("enter card api get home fallback"); CountVo countVo = new CountVo(); countVo.setCardCount(1); countVo.setFileCount(1); countVo.setPointCount(1); return resultUtil.success2obj(countVo,"success"); } } ``` ## 配置相关 ### 全局启用 ~~~ feign.hystrix.enabled: true ~~~ #### 全局禁用 ~~~ feign.hystrix.enabled: false ~~~ ### 局部启用 ~~~ public class FeignEnableHystrixConfiguration { @Bean @Scope("prototype") public HystrixFeign.Builder feignBuilder() { return HystrixFeign.builder(); } } ~~~ ~~~ @FeignClient(name = "mic-card",path = "/card/admin", configuration = {FeignEnableHystrixConfiguration.class}, fallback = CardApiFallback.class) ~~~ ## 局部禁用 ~~~ public class FeignDisableHystrixConfiguration { @Bean @Scope("prototype") public Feign.Builder feignBuilder() { return Feign.builder(); } } ~~~ ## @HystrixCommand注解源码 ``` java /** * This annotation used to specify some methods which should be processes as hystrix commands. */ @Target({ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Inherited @Documented public @interface HystrixCommand { /** * The command group key is used for grouping together commands such as for reporting, * alerting, dashboards or team/library ownership. * <p/> * default => the runtime class name of annotated method * * @return group key */ String groupKey() default ""; /** * Hystrix command key. * <p/> * default => the name of annotated method. for example: * <code> * ... * @HystrixCommand * public User getUserById(...) * ... * the command name will be: 'getUserById' * </code> * * @return command key */ String commandKey() default ""; /** * The thread-pool key is used to represent a * HystrixThreadPool for monitoring, metrics publishing, caching and other such uses. * * @return thread pool key */ String threadPoolKey() default ""; /** * Specifies a method to process fallback logic. * A fallback method should be defined in the same class where is HystrixCommand. * Also a fallback method should have same signature to a method which was invoked as hystrix command. * for example: * <code> * @HystrixCommand(fallbackMethod = "getByIdFallback") * public String getById(String id) {...} * * private String getByIdFallback(String id) {...} * </code> * Also a fallback method can be annotated with {@link HystrixCommand} * <p/> * default => see {@link com.netflix.hystrix.contrib.javanica.command.GenericCommand#getFallback()} * * @return method name */ String fallbackMethod() default ""; /** * Specifies command properties. * * @return command properties */ HystrixProperty[] commandProperties() default {}; /** * Specifies thread pool properties. * * @return thread pool properties */ HystrixProperty[] threadPoolProperties() default {}; /** * Defines exceptions which should be ignored. * Optionally these can be wrapped in HystrixRuntimeException if raiseHystrixExceptions contains RUNTIME_EXCEPTION. * * @return exceptions to ignore */ Class<? extends Throwable>[] ignoreExceptions() default {}; /** * Specifies the mode that should be used to execute hystrix observable command. * For more information see {@link ObservableExecutionMode}. * * @return observable execution mode */ ObservableExecutionMode observableExecutionMode() default ObservableExecutionMode.EAGER; /** * When includes RUNTIME_EXCEPTION, any exceptions that are not ignored are wrapped in HystrixRuntimeException. * * @return exceptions to wrap */ HystrixException[] raiseHystrixExceptions() default {}; /** * Specifies default fallback method for the command. If both {@link #fallbackMethod} and {@link #defaultFallback} * methods are specified then specific one is used. * note: default fallback method cannot have parameters, return type should be compatible with command return type. * * @return the name of default fallback method */ String defaultFallback() default ""; } ``` ## 参考资料 * https://www.itmuch.com/spring-cloud/finchley-13/