摘要：實戰五概要什么是怎么用常見配置介紹什么是是分布式系統處理超時和錯誤的機制如下圖所示分布式系統中某個用戶請求依賴服務當此請求并發超過的時候服務處理速度變慢但是服務還是被調用大量請求會阻塞在服務器上影響其它整個服務在復雜的分布式架構的應用程序

什么是Spring Cloud Netflix Hystrix?

怎么用 Spring Cloud Netflix Hystrix?

Hystrix常見配置介紹

Spring Cloud Netflix Hystrix是分布式系統處理超時和錯誤的機制,如下圖所示,分布式系統中某個用戶請求依賴A,H,I,P服務.

當此請求并發超過50的時候,服務I處理速度變慢,但是服務I還是被調用.


大量請求會阻塞在Tomcat服務器上,影響其它整個服務.在復雜的分布式架構的應用程序有很多的依賴,都會不可避免地在某些時候失敗.高并發的依賴失敗時如果沒有隔離措施,當前應用服務就有被拖垮的風險.
Spring Cloud Netflix Hystrix就是隔離措施的一種實現,可以設置在某種超時或者失敗情形下斷開依賴調用或者返回指定邏輯,從而提高分布式系統的穩定性.

百說不如一run,構造一個例子來實現,例子要實現使用Hystrix的Fallback(失敗后)邏輯來處理錯誤情景
1.Eureka Server,和Eureka Client跟之前一樣,只需改造Eureka Sentence
2.Eureka Sentence 添加pom依賴

        
            org.springframework.cloud
            spring-cloud-starter-hystrix
        
        
            org.springframework.cloud
            spring-cloud-starter-hystrix-dashboard
        

3.Eureka Sentence的Application添加hystrix注解

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@EnableHystrix
@EnableHystrixDashboard
public class ApplicationSentence {
    public static void main(String[] args) {
        SpringApplication.run(ApplicationSentence.class, args);
    }
}

4.Eureka Sentence WordServiceImpl在subject,adjective,noun上添加HystrixCommand注解并實現相應的fallback邏輯.

@Service
public class WordServiceImpl implements WordService {

    @Autowired
    VerbClient verbClient;
    @Autowired
    SubjectClient subjectClient;
    @Autowired
    ArticleClient articleClient;
    @Autowired
    AdjectiveClient adjectiveClient;
    @Autowired
    NounClient nounClient;
   

    @Override
    @HystrixCommand(fallbackMethod="getFallbackSubject")
    public String getSubject() {
        return subjectClient.getWord();
    }



    @Override
    public String getVerb() {
        return verbClient.getWord();
    }

    @Override
    public String getArticle() {
        return articleClient.getWord();
    }

    @Override
    @HystrixCommand(fallbackMethod="getFallbackAdjective")
    public String getAdjective() {
        return adjectiveClient.getWord();
    }

 
    @HystrixCommand(fallbackMethod="getFallbackNoun")
    public String getNoun() {
        return nounClient.getWord();
    }

    public String getFallbackSubject() {
        return "某人";
    }

    public String getFallbackAdjective() {
        return "";
    }

    public String getFallbackNoun() {
        return "某物";
    }
}

5.依次啟動Eureka Server,Eureka Client,Eureka Sentence,這個跟之前一樣造句,停掉subject,noun服務,可以看到其可以走fallback邏輯.
6.使用異步和reactive形式的Hystrix,修改getSubject()為Future,修改getNoun()為Observable.SentenceServiceImpl也做相應的修改.

@Service
public class WordServiceImpl implements WordService {

    @Autowired
    VerbClient verbClient;
    @Autowired
    SubjectClient subjectClient;
    @Autowired
    ArticleClient articleClient;
    @Autowired
    AdjectiveClient adjectiveClient;
    @Autowired
    NounClient nounClient;
    @Override
    @HystrixCommand(fallbackMethod = "getFallbackSubject")
    public Future getSubject() {
        return new AsyncResult() {
            @Override
            public String invoke() {
                return subjectClient.getWord();
            }
        };
    }

//    @Override
//    @HystrixCommand(fallbackMethod="getFallbackSubject")
//    public String getSubject() {
//        return subjectClient.getWord();
//    }



    @Override
    public String getVerb() {
        return verbClient.getWord();
    }

    @Override
    public String getArticle() {
        return articleClient.getWord();
    }

    @Override
    @HystrixCommand(fallbackMethod="getFallbackAdjective")
    public String getAdjective() {
        return adjectiveClient.getWord();
    }

    @Override
    @HystrixCommand(fallbackMethod="getFallbackNoun")
    public Observable getNoun() {
        return Observable.create(new Observable.OnSubscribe() {
            @Override
            public void call(Subscriber observer) {
                try {
                    if (!observer.isUnsubscribed()) {
                        observer.onNext(nounClient.getWord());
                        observer.onCompleted();
                    }
                } catch (Exception e) {
                    observer.onError(e);
                }
            }
        });
    }
//    @HystrixCommand(fallbackMethod="getFallbackNoun")
//    public String getNoun() {
//        return nounClient.getWord();
//    }

    public String getFallbackSubject() {
        return "某人";
    }

    public String getFallbackAdjective() {
        return "";
    }

    public String getFallbackNoun() {
        return "某物";
    }
}

SentenceServiceImpl修改成下面

@Service
public class SentenceServiceImpl implements SentenceService {

    @Autowired WordService wordService;


    /**
     * Assemble a sentence by gathering random words of each part of speech:
     */
    public String buildSentence() {

        final List nounList = Lists.newArrayList();
        wordService.getNoun().subscribe(new Subscriber() {
            @Override
            public void onCompleted() {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onNext(String s) {
                nounList.add(s);
            }
        });

        try {
            return String.format("%s %s %s %s %s.", wordService.getSubject().get(), wordService.getVerb(),
                    wordService.getArticle(), wordService.getAdjective(), nounList.get(0));
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        return "error";
    }

}

7.查看Hystrix dashboard可以看到方法調用的統計信息
訪問http://127.0.0.1:8020/hystrix并輸入http://127.0.0.1:8020/hystrix...可以查看Hystrix接口調用信息