SpringCloud the fuse -Hystrix

Hystrix is ​​a delay and fault-tolerant database, designed to isolate the access point to remote systems, services and third-party libraries, stop cascading failure, and to achieve flexibility in complex distributed systems, in these systems, failure is inevitable .

rely

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

SpringBootApplication entrance need to add @EnableCircuitBreakernotes, then Spring AOP factory will start on the way there are all methods @HystrixCommandto add fuse strategic business approach.

@SpringBootApplication
@EnableCircuitBreaker
public class HystrixSpringBootApplication {
    public static void main(String[] args) {
        SpringApplication.run(HystrixSpringBootApplication.class,args);
    }
}

Add on business method @HystrixCommandNotes realized blown.

@HystrixCommand
@Override
public User queryUserById(Integer id) {
    System.out.println(Thread.currentThread().getId());
    return new User("未熔断", new Date(), true, 11.11);
}

Thread isolation

The default method of execution will start a new thread of execution and the main program is not a thread, so if there is ThreadLocal variable context, in this method becomes ineffective. So generally annotation property by setting commandProperties, set the thread on it.

• By default thread ID Service and the Controller
  

@HystrixCommand(commandProperties = {
            @HystrixProperty(name = "execution.isolation.strategy",value = "SEMAPHORE")
    })
@Override
public User queryUserById(Integer id) {
	System.out.println("Service线程ID:" + Thread.currentThread().getId());
    return new User("未熔断", new Date(), true, 11.11);
}

• After setting the thread ID Service and the Controller
  

execution.isolation.strategyAlternatively value of this attribute has two THREADand SEMAPHOREdefault values THREAD. ① general if there is a second instance of a 100 concurrent, this time because of frequent start threads overhead is too large at this time generally consider SEMAPHORE, ② non-network calls.

Fallback

Over the @HystrixCommand中声明fallbackMethodname of graceful degradation may be achieved as follows:

@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById")
@Override
public User queryUserById(Integer id) {
    System.out.println(Thread.currentThread().getId());
    int i=10/0;
    return new User("未熔断", new Date(), true, 11.11);
}
public User fallbackMethodQueryUserById(Integer id, Throwable e) {
    System.out.println(e.getMessage());
    return new User("熔断降级后", new Date(), true, 11.11);
}

Result of the call:

Note that the target method and the method in claim fallbackMethod must be in the same class having the same parameters (abnormal parameter optional)

Error Propagation

According to this description, @ HystrixCommandbe able to specify the type of exception should be ignored. The following ArithmeticException: / by zerowill not trigger fallbackMethod method.

//	@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById")
//	@HystrixCommand(commandProperties = {
//			@HystrixProperty(name = "execution.isolation.strategy", value = "SEMAPHORE")
//	})
	@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById",ignoreExceptions = {ArithmeticException.class})
	@Override
	public User getUser(Integer id) {
		System.out.println("Service线程ID:" + Thread.currentThread().getId());
		int i = 10 / 0;
		return new User("未熔断", new Date(), true, 11.11);
	}

	public User fallbackMethodQueryUserById(Integer id, Throwable e) {
		System.out.println(e.getMessage());
		return new User("熔断降级后", new Date(), true, 11.11);
	}

Request timed out fuse

The user can set the execution.isolation.thread.timeoutInMillisecondsproperty of a requested maximum delay method, the system will throwHystrixTimeoutException

@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById",commandProperties = {
			@HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="100")
	})
	@Override
	public User getUser(Integer id) {
		System.out.println("Service线程ID:" + Thread.currentThread().getId());
		try {
			Thread.sleep(500);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
//		int i = 10 / 0;
		return new User("未熔断", new Date(), true, 11.11);
	}

	public User fallbackMethodQueryUserById(Integer id, Throwable e) {
		System.out.println(e.getMessage());
		return new User("超时熔断", new Date(), true, 11.11);
	}

Results of the:

https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-javanica
https://github.com/Netflix/Hystrix/wiki/Configuration

Hystrix Dashboard

rely

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

SpringBoot entrance class to add @EnableHystrixDashboardannotations
to access the page http: // localhost: port / hystrix