1 Hystrix 簡介

在微服務(wù)架構(gòu)中叶圃，微服務(wù)之間通過網(wǎng)絡(luò)進行通信，存在相互依賴践图，當(dāng)其中一個服務(wù)不可用時掺冠，有可能會造成雪崩效應(yīng)。要防止這樣的情況码党，必須要有容錯機制來保護服務(wù)德崭。
Hystrix是Netflix開源的一個延遲和容錯庫，它主要實現(xiàn)了以下幾點：

包裹請求
使用HystrixCommand（或HystrixObservableCommand）包裹對依賴的調(diào)用邏輯揖盘，每個命令在獨立線程中執(zhí)行眉厨。
跳閘機制
當(dāng)某服務(wù)的錯誤率超過一定閾值時，Hystrix可以自動或手動跳閘扣讼，停止請求該服務(wù)一段時間缺猛。
資源隔離
Hystrix為每個依賴都維護了一個小型的線程池（或信號量），如果該線程池已滿椭符，發(fā)往該依賴的請求就被立即拒絕荔燎。
監(jiān)控
Hystrix可以近乎實時地監(jiān)控運行指標(biāo)和配置的變化。
回退機制
當(dāng)請求失敗销钝、超時有咨、被拒絕，或者當(dāng)斷路器打開時蒸健，執(zhí)行回退邏輯座享。
自我修復(fù)
當(dāng)斷路器打開一段時間后，會自動進入“半打開”狀態(tài)似忧，允許一個請求訪問依賴的服務(wù)渣叛，如果該請求成功，則關(guān)閉斷路器盯捌，否則繼續(xù)保持打開狀態(tài)淳衙。

2 整合Hystrix

2.1 Ribbon整合Hystrix

1.添加相應(yīng)的依賴：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix</artifactId>
        </dependency>

2.在啟動類里添加@EnableCircuitBreaker 或者 @EnableHystrix注解

@EnableCircuitBreaker
@EnableDiscoveryClient
@SpringBootApplication
public class RibbonDemoApplication {

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }



    public static void main(String[] args) {
        SpringApplication.run(RibbonDemoApplication.class, args);
    }
}

3.為需要容錯的方法添加@HystrixCommand注解，并使用fallbackMethod屬性指定回退方法

    @HystrixCommand(fallbackMethod = "errorFallback")
    @GetMapping("/hello")
    public String hello() {

        return this.restTemplate.getForObject("http://eureka-client-demo/hello", String.class);
    }


    public String errorFallback() {
        return "Error!";
    }

@HystrixCommand的配置類似下面：

@HystrixCommand(fallbackMethod = "stubMyService",
    commandProperties = {
      @HystrixProperty(name="execution.isolation.strategy", value="SEMAPHORE")
    }
)

2.2 Feign使用Hystrix

1.Spring Cloud 中饺著，F(xiàn)eign默認已經(jīng)整合了Hystrix箫攀，所以只需要在配置中啟用Hystrix就會包裹全部Feign Client中的方法：

feign:
  hystrix:
    enabled: true

2.編寫回退方法，編寫一個Feign Client的實現(xiàn)類幼衰，在@FeignClient的fallback屬性指定對應(yīng)的類：

@FeignClient(name = "eureka-client-demo", fallback = ErrorFallback.class)
public interface DemoFeignClient {

    @GetMapping("/hello")
    public String hello();
}


@Component
public class ErrorFallback implements DemoFeignClient {

    @Override
    public String hello() {
        return "Error!";
    }
}

3.如果需要回退方法打印錯誤信息靴跛，可以使用fallbackFactory（fallback和fallbackFactory只能使用其中一種）：

@FeignClient(name = "eureka-client-demo", fallbackFactory = ErrorFallbackFactory.class)
public interface DemoFeignClient {

    @GetMapping("/hello")
    public String hello();
}


@Component
public class ErrorFallbackFactory implements FallbackFactory<DemoFeignClient> {

    private static final Logger LOGGER = LoggerFactory.getLogger(ErrorFallbackFactory.class);

    @Override
    public DemoFeignClient create(Throwable throwable) {
        return new DemoFeignClient() {
            @Override
            public String hello() {
                //如果在create()中打印錯誤信息的話，在應(yīng)用程序啟動時就會打印
                ErrorFallbackFactory.LOGGER.info("fall back cause: ", throwable);
                return "Error!";
            }
        };
    }
}

4.如果不想某個Feign Client使用Hystrix的話渡嚣，可以使用如下配置：

@FeignClient(name = "eureka-client-demo", configuration = DisableHystrix.class)
public interface DemoFeignClient {

    @GetMapping("/hello")
    public String hello();
}

@Configuration
public class DisableHystrix {

    @Bean
    @Scope("prototype")
    public Feign.Builder feignBuilder() {
        return Feign.builder();
    }
}

3 Hystrix監(jiān)控

3.1 Ribbon中Hystrix的監(jiān)控

Hystrix提供了端點/hystrix.stream用于監(jiān)控Hystrix的情況梢睛，Ribbon在整合了Hystrix之后肥印，還需要引入Spring Boot 的actuator依賴，才能通過/hystrix.stream監(jiān)控接口運行情況绝葡。

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

/hystrix.stream的頁面會返回類似下面的監(jiān)控數(shù)據(jù)：

data: {"type":"HystrixCommand","name":"hello","group":"Controller","currentTime":1516202320578,"isCircuitBreakerOpen":false,"errorPercentage":100,"errorCount":1,"requestCount":1,"rollingCountBadRequests":0,"rollingCountCollapsedRequests":0,"rollingCountEmit":0,"rollingCountExceptionsThrown":0,"rollingCountFailure":1,"rollingCountFallbackEmit":0,"rollingCountFallbackFailure":0,"rollingCountFallbackMissing":0,"rollingCountFallbackRejection":0,"rollingCountFallbackSuccess":1,"rollingCountResponsesFromCache":0,"rollingCountSemaphoreRejected":0,"rollingCountShortCircuited":0,"rollingCountSuccess":0,"rollingCountThreadPoolRejected":0,"rollingCountTimeout":0,"currentConcurrentExecutionCount":0,"rollingMaxConcurrentExecutionCount":0,"latencyExecute_mean":0,"latencyExecute":{"0":0,"25":0,"50":0,"75":0,"90":0,"95":0,"99":0,"99.5":0,"100":0},"latencyTotal_mean":0,"latencyTotal":{"0":0,"25":0,"50":0,"75":0,"90":0,"95":0,"99":0,"99.5":0,"100":0},"propertyValue_circuitBreakerRequestVolumeThreshold":20,"propertyValue_circuitBreakerSleepWindowInMilliseconds":5000,"propertyValue_circuitBreakerErrorThresholdPercentage":50,"propertyValue_circuitBreakerForceOpen":false,"propertyValue_circuitBreakerForceClosed":false,"propertyValue_circuitBreakerEnabled":true,"propertyValue_executionIsolationStrategy":"THREAD","propertyValue_executionIsolationThreadTimeoutInMilliseconds":1000,"propertyValue_executionTimeoutInMilliseconds":1000,"propertyValue_executionIsolationThreadInterruptOnTimeout":true,"propertyValue_executionIsolationThreadPoolKeyOverride":null,"propertyValue_executionIsolationSemaphoreMaxConcurrentRequests":10,"propertyValue_fallbackIsolationSemaphoreMaxConcurrentRequests":10,"propertyValue_metricsRollingStatisticalWindowInMilliseconds":10000,"propertyValue_requestCacheEnabled":true,"propertyValue_requestLogEnabled":true,"reportingHosts":1,"threadPool":"Controller"}

3.2 Feign中Hystrix的監(jiān)控

1.雖然Feign整合了Hystrix竖独，但是并沒有整合到監(jiān)控的模塊，所以我們需要重新引入依賴包：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

2.在啟動類添加@EnableCircuitBreaker或者@EnableHystrix注解

@EnableCircuitBreaker
@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication
public class FeignDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(FeignDemoApplication.class, args);
    }
}

然后就可以通過端點/hystrix.stream查看監(jiān)控數(shù)據(jù)挤牛。

4 可視化監(jiān)控

4.1 監(jiān)控單個服務(wù)

可以使用hystrix-dashboard進行可視化監(jiān)控：
1.創(chuàng)建一個新項目，并引入以下依賴：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix-dashboard</artifactId>
        </dependency>

在啟動類加上@EnableHystrixDashboard注解

@EnableHystrixDashboard
@SpringBootApplication
public class HystrixDashboardApplication {

    public static void main(String[] args) {
        SpringApplication.run(HystrixDashboardApplication.class, args);
    }
}

3.啟動應(yīng)用种蘸，打開/hystrix/端點墓赴，可以看到一下頁面：

hystix-dashboard.PNG

往url欄輸入/hystrix.stream的鏈接，如：http://localhost:8004/hystrix.stream航瞭，再點擊Monitor Stream按鈕诫硕，就可以看到如下圖的頁面：

hystix-dashboard-detail.PNG

4.2 監(jiān)控多個服務(wù)

上面的方法只能監(jiān)控單個服務(wù)，如果要監(jiān)控多個服務(wù)刊侯，可以使用turbine章办，然后再使用hystrix-dashboard進行進行可視化監(jiān)控。
1.新建一個項目滨彻，引入turbine的依賴

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-turbine</artifactId>
        </dependency>

2.在啟動類添加@EnableTurbine注解

@EnableTurbine
@SpringBootApplication
public class TurbineApplication {

    public static void main(String[] args) {
        SpringApplication.run(TurbineApplication.class, args);
    }
}

3.配置文件：

server:
  port: 8006
spring:
  application:
    name: turbine
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8001/eureka/
  instance:
    prefer-ip-address: true

turbine:
  app-config: feign-demo,ribbon-demo
  cluster-name-expression: "'default'"
  combine-host-port: true

app-config 指定需要監(jiān)控的服務(wù)藕届，用逗號分隔
cluster-name-expression 指定集群名稱
combine-host-port 按主機名和端口區(qū)分服務(wù)，turbine默認相同host的為同一服務(wù)亭饵，將該屬性設(shè)為true后就可以按主機名和端口區(qū)分服務(wù)

4.啟動應(yīng)用休偶，打開/turbine.stream端點即可以看到兩者的監(jiān)控數(shù)據(jù)。這個時候辜羊，再將turbine的監(jiān)控數(shù)據(jù)接入hystrix-dashboard踏兜，比如，將url地址http://localhost:8006/turbine.stream填入dash-board的url一欄八秃，再點擊Monitor Stream按鈕碱妆，就可以同時看到兩個服務(wù)的監(jiān)控數(shù)據(jù)。

4.3 使用消息中間件收集數(shù)據(jù)（RabbitMQ）

提供服務(wù)的微服務(wù)添加以下依賴：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-netflix-hystrix-stream</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
        </dependency>

添加RabbitMQ的配置：

spring:
  rabbitmq:
    host: localhost
    port: 5672
    username: guest
    password: guest

Turbine項目移除turbine的依賴并添加以下依賴：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-turbine-stream</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
        </dependency>

啟動類中@EnableTurbine修改為@EnableTurbineStream
添加RabbitMQ的配置昔驱，同2疹尾，同時去掉turbine的配置。

Hystrix——服務(wù)容錯