簡(jiǎn)介

微服務(wù)結(jié)構(gòu)中玄窝，服務(wù)調(diào)用其他服務(wù)垒迂，如果服務(wù)提供者不可用械姻，會(huì)引起服務(wù)調(diào)用者不可用，進(jìn)而引起整個(gè)調(diào)用鏈上所有的服務(wù)可用机断，熔斷器提供了服務(wù)提供者不可用時(shí)楷拳，服務(wù)調(diào)用者能夠快速返回的機(jī)制
這里簡(jiǎn)單介紹resilience4j-cricuit breaker的使用，包括在sping boot中使用yml文件配置熔斷器和注解@CircuitBreaker使用熔斷器

基本功能

resilence4j-circuit breaker 熔斷器包括三個(gè)狀態(tài)：關(guān)閉吏奸、開啟欢揖、半開。

• 服務(wù)正常情況下熔斷器處于關(guān)閉狀態(tài)奋蔚，一切正常浸颓，
• 在熔斷器判斷服務(wù)不可達(dá)時(shí)進(jìn)入開啟狀態(tài)，服務(wù)將拒絕請(qǐng)求旺拉，轉(zhuǎn)而執(zhí)行fallback方法返回产上，
• 在開啟狀態(tài)固定時(shí)間之后，熔斷器進(jìn)入半開狀態(tài)蛾狗，服務(wù)將接受固定個(gè)數(shù)的請(qǐng)求晋涣，熔斷器根據(jù)這些請(qǐng)求執(zhí)行的失敗概率來(lái)決定是進(jìn)入開啟狀態(tài)還是關(guān)閉狀態(tài)

熔斷器統(tǒng)計(jì)失敗率

resilience4j 默認(rèn)是使用基于請(qǐng)求數(shù)量的滑動(dòng)窗口統(tǒng)計(jì)失敗率，具體數(shù)量可配置沉桌，默認(rèn)配置為100谢鹊，resilience4j只統(tǒng)計(jì)最新的100個(gè)請(qǐng)求的成功失敗情況，如果有新的請(qǐng)求最老的請(qǐng)求會(huì)被踢出

配置詳解

演示使用

1. 創(chuàng)建一個(gè)模擬的外部服務(wù)篮奄，前10次調(diào)用成功捆愁，后面的調(diào)用返回異常
2. 自定義CircuitBreakerConfig，修改滑動(dòng)窗口大小為10窟却，默認(rèn)情況下50%的調(diào)用失敗會(huì)進(jìn)入開啟狀態(tài)昼丑，修改熔斷器從開啟到半開啟時(shí)間為10s
3. 每隔1秒使用熔斷器調(diào)用一次模擬服務(wù)

需要準(zhǔn)備的依賴包，resilience4j的spring boot包夸赫，里面包括了resilience4j所有功能的包和自動(dòng)配置功能

<dependency>
    <groupId>io.github.resilience4j</groupId>
    <artifactId>resilience4j-spring-boot2</artifactId>
    <version>1.7.0</version>
</dependency>

模擬服務(wù)

服務(wù)和自定義的異常：BadProcessingException

@Service
public class ExternalService {
    private int count = 0;

    public String callService() {
        count++;
        if (count <= 10) {
            return "success";
        } else {
            throw new BadProcessingException("request fail.");
        }
    }

}

class BadProcessingException extends RuntimeException {
    public BadProcessingException(String message) {
        super(message);
    }
}

熔斷器配置和使用

在test方法中配置熔斷器和調(diào)用外部服務(wù)

@SpringBootTest
class CircuitBreakerBasicsTest {
    @Autowired
    ExternalService externalService;

    @Test
    void cbService() {
        // 創(chuàng)建熔斷器的自定義配置
        CircuitBreakerConfig config = CircuitBreakerConfig.custom()
            // 修改滑動(dòng)窗口大小
            .slidingWindowSize(10)
            // 修改從開啟狀態(tài)到半開的時(shí)間
            .waitDurationInOpenState(Duration.ofSeconds(10)).build();
        // 創(chuàng)建熔斷器使用自定義配置
        CircuitBreaker circuitBreaker = CircuitBreaker.of("circuitBreaker", config);
        for (int i = 0; i < 50; i++) {
            try {
                Thread.sleep(1000);
                System.out.println("count = " + (i + 1));
                // 熔斷器執(zhí)行外部服務(wù), 記錄下服務(wù)返回值
                String status = circuitBreaker.executeSupplier(externalService::callService);
                System.out.println(status);
            } catch (Exception e) {
                // 打印異常的全限定名稱
                System.err.println(e.getClass().getName());
            } finally {
                // 打印執(zhí)行過程中熔斷器具體的信息
                System.out.println("Successful call count: " + circuitBreaker.getMetrics().getNumberOfSuccessfulCalls()
                    + " | failed call count: " + circuitBreaker.getMetrics().getNumberOfFailedCalls()
                    + " | failure rate %:" + circuitBreaker.getMetrics().getFailureRate()
                    + " | state: " + circuitBreaker.getState());
                System.out.println("-----------------------------------------------------------------------------");
            }
        }
    }
}

輸出結(jié)果

• 前10次調(diào)用返回成功菩帝，熔斷器處于關(guān)閉狀態(tài)，滑動(dòng)窗口中成功的調(diào)用次數(shù)累積到10次
• 11-15次調(diào)用返回自定義的異常BadProcessingException茬腿，滑動(dòng)窗口中失敗的調(diào)用次數(shù)開始增加呼奢，成功的次數(shù)減少，在第15次調(diào)用時(shí)達(dá)到了50%的失敗閾值切平，熔斷器開啟
• 16-24次調(diào)用返回的是熔斷器的異常CallNotPermittedException握础，調(diào)用被拒絕，滑動(dòng)窗口中的調(diào)用次數(shù)不會(huì)變化
• 第25次調(diào)用悴品，此時(shí)經(jīng)過了10s熔斷器從開啟轉(zhuǎn)為了半開狀態(tài)禀综，熔斷器將接受10次調(diào)用，可以看到返回的異常是BadProcessingException
• 之后10次調(diào)用全部失敗苔严，熔斷器又轉(zhuǎn)為開啟狀態(tài)定枷，之后一直在開啟和半開之間轉(zhuǎn)換

輸出結(jié)果太長(zhǎng)，只貼出其中的一部分

count = 10
success
Successful call count: 10 | failed call count: 0 | failure rate %:0.0 | state: CLOSED
-----------------------------------------------------------------------------
count = 11
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 9 | failed call count: 1 | failure rate %:10.0 | state: CLOSED
-----------------------------------------------------------------------------
count = 12
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 8 | failed call count: 2 | failure rate %:20.0 | state: CLOSED
-----------------------------------------------------------------------------
count = 13
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 7 | failed call count: 3 | failure rate %:30.0 | state: CLOSED
-----------------------------------------------------------------------------
count = 14
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 6 | failed call count: 4 | failure rate %:40.0 | state: CLOSED
-----------------------------------------------------------------------------
count = 15
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 16
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 17
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 18
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 19
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 20
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 21
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 22
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 23
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 24
io.github.resilience4j.circuitbreaker.CallNotPermittedException
Successful call count: 5 | failed call count: 5 | failure rate %:50.0 | state: OPEN
-----------------------------------------------------------------------------
count = 25
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 0 | failed call count: 1 | failure rate %:-1.0 | state: HALF_OPEN
-----------------------------------------------------------------------------
count = 26
io.ysh.eurekacientconsumer.service.BadProcessingException
Successful call count: 0 | failed call count: 2 | failure rate %:-1.0 | state: HALF_OPEN
-----------------------------------------------------------------------------

springboot 自動(dòng)配置

配置文件+注解使用熔斷器

在application.yml文件中加入如下配置

• configs中是熔斷器配置列表届氢，可以配置多個(gè)熔斷器配置依鸥，default是其中一個(gè)
• instans中是熔斷器的名稱，可以配置多個(gè)悼沈，用于注解中標(biāo)注service使用的是哪個(gè)熔斷器贱迟，baseConfig指定了使用的配置名稱，就是configs中的絮供；也可以指定配置項(xiàng)衣吠，會(huì)覆蓋configs中的同名配置項(xiàng)
• Predicate和Exception需要配置為全限定名稱，Predicate只能配置一個(gè)壤靶，Exceptions可以配置多個(gè)缚俏，按列表的形式配置；測(cè)試代碼中沒有使用到贮乳，這里只是展示下怎樣配置

resilience4j.circuitbreaker:
  configs:
    default:
      slidingWindowSize: 10
      waitDurationInOpenState: 10s
      failureRateThreshold: 50
  instances:
    externalService:
      baseConfig: default
      permittedNumberOfCallsInHalfOpenState: 10
      recordFailurePredicate: io.github.robwin.exception.RecordFailurePredicate
      recordExceptions:
        - org.springframework.web.client.HttpServerErrorException
        - java.util.concurrent.TimeoutException
        - java.io.IOException

在service方法上使用@CircuitBreaker注解

• name：指定熔斷器的名稱忧换，就是配置文件中instances下的externalService
• fallbackMethod：熔斷器開啟時(shí)，service拒絕調(diào)用向拆，會(huì)調(diào)用fallback方法返回信息

@CircuitBreaker(name = "externalService", fallbackMethod = "fallback")
public String callService() {
    count++;
    if (count <= 10) {
        return "success";
    } else {
        throw new BadProcessingException("request fail.");
    }
}

public String fallback(Throwable throwable) {
    return "fallback";
}

在下面的測(cè)試代碼中就不需要自行創(chuàng)建熔斷器了亚茬，需要打印熔斷器具體信息的話需要注入 CircuitBreakerRegistry Bean，使用circuitBreaker方法傳入熔斷器名稱即可
下面的測(cè)試代碼中沒有顯示的使用熔斷器浓恳，輸出的結(jié)果中原本的異常輸出都變成了fallbackMethod方法的返回刹缝，除此之外都一樣碗暗，將注解中的fallbackMethod去掉輸出結(jié)果就跟之前完全一樣了

@SpringBootTest
class CircuitBreakerBasicsTest {
    @Autowired
    ExternalService externalService;

    @Autowired
    CircuitBreakerRegistry circuitBreakerRegistry;

    @Test
    void cbService() {
        // 獲取熔斷器，在externalService方法調(diào)用中沒有也不需要使用這個(gè)顯式的引用梢夯，這個(gè)只用于具體信息的獲取
        CircuitBreaker circuitBreaker = circuitBreakerRegistry.circuitBreaker("externalService");
        for (int i = 0; i < 50; i++) {
            try {
                Thread.sleep(1000);
                System.out.println("count = " + (i + 1));
                String status = externalService.callService();
                System.out.println(status);
            } catch (Exception e) {
                // 打印異常的全限定名稱
                System.err.println(e.getClass().getName());
            } finally {
                // 打印執(zhí)行過程中熔斷器具體的信息
                System.out.println("Successful call count: " + circuitBreaker.getMetrics().getNumberOfSuccessfulCalls()
                    + " | failed call count: " + circuitBreaker.getMetrics().getNumberOfFailedCalls()
                    + " | failure rate %:" + circuitBreaker.getMetrics().getFailureRate()
                    + " | state: " + circuitBreaker.getState());
                System.out.println("-----------------------------------------------------------------------------");
            }
        }
    }
}