# Spring Cloud Circuit Breaker
Spring Cloud Circuit Breaker项目包含Resilience4J实现和Spring Retry实现。
## 配置Resilience4J Circuit Breakers
关于resilience4J Circuit Breakers实现，拥有如下两个启动器，一个用于响应式项目，另一个用于非响应式项目：
- `org.springframework.cloud:spring-cloud-starter-circuitbreaker-resilience4j`
- `org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j`

### 关闭自动装配
可以通过设置`spring.cloud.circuitbreaker.resilience4j.enabled`为false来关闭Resilience4J的自动装配
### 默认配置
如果想要为所有的circuit breaker提供默认配置，可以创建一个`Customizer` bean对象，该bean对象接收一个`Resilience4JCircuitBreakerFactory`类型参数。configureDefault方法可以用于提供默认的配置：
```java
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> defaultCustomizer() {
    return factory -> factory.configureDefault(id -> new Resilience4JConfigBuilder(id)
            .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(4)).build())
            .circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
            .build());
}
```
### 自定义ExecutorService
如果想要自定义执行circuit breaker的`ExecutorService`，可以通过Resilience4JCircuitBreakerFactor来指定。  
例如，想要指定一个context aware ExecutorService，可以按如下所示：
```java
@Bean
public Customizer<ReactiveResilience4JCircuitBreakerFactory> defaultCustomizer() {
    return factory -> {
        ContextAwareScheduledThreadPoolExecutor executor = ContextAwareScheduledThreadPoolExecutor.newScheduledThreadPool().corePoolSize(5)
            .build();
        factory.configureExecutorService(executor);
    };
}
```
### 指定Circuit Breaker 配置
类似为所有Circuit Breakers指定默认配置，也能以如下方式为特定Circuit Breaker指定配置：
```java
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> slowCustomizer() {
    return factory -> factory.configure(builder -> builder.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
            .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(2)).build()), "slow");
}
```
### Circuit Breaker属性配置
可以在配置文件中指定`CircuitBreaker`和`TimeLimiter`配置，配置文件中指定的配置比Customizer中指定的配置优先级更高。  
优先级从上到下递减：
- 方法级别(id)配置 - 针对指定的方法或操作
- service级别（group）配置 - 针对指定应用的service或操作
- 全局默认配置

#### 全局默认
```yml
resilience4j.circuitbreaker:
    configs:
        default:
            registerHealthIndicator: true
            slidingWindowSize: 50

resilience4j.timelimiter:
    configs:
        default:
            timeoutDuration: 5s
            cancelRunningFuture: true
```
#### Configs Properties Configuration
```yml
resilience4j.circuitbreaker:
    configs:
        groupA:
            registerHealthIndicator: true
            slidingWindowSize: 200

resilience4j.timelimiter:
    configs:
        groupC:
            timeoutDuration: 3s
            cancelRunningFuture: true
```
#### 实例属性设置
```yml
resilience4j.circuitbreaker:
 instances:
     backendA:
         registerHealthIndicator: true
         slidingWindowSize: 100
     backendB:
         registerHealthIndicator: true
         slidingWindowSize: 10
         permittedNumberOfCallsInHalfOpenState: 3
         slidingWindowType: TIME_BASED
         recordFailurePredicate: io.github.robwin.exception.RecordFailurePredicate

resilience4j.timelimiter:
 instances:
     backendA:
         timeoutDuration: 2s
         cancelRunningFuture: true
     backendB:
         timeoutDuration: 1s
         cancelRunningFuture: false
```