SatyaCodes

Hystrix Circuit Breaker

Hystrix Circuit Breaker

Spring Cloud Circuit Breaker using Netflix Hystrix

In the microservices world, to fulfill a client request one microservice may need to talk to other microservices. We should minimize this kind of direct dependencies on other microservices but in some cases it is unavoidable. If a microservice is down or not functioning properly then the issue may cascade up to the upstream services.

Netflix created Hystrix library implementing Circuit Breaker pattern to address these kinds of issues. We can use Spring Cloud Netflix Hystrix Circuit Breaker to protect microservices from cascading failures.

Steps to Spring Cloud Circuit Breaker using Netflix Hystrix

From EDC-Micrservice we are invoking REST endpoint on MI-service to testReports of the user. What if Mi-service is down? What if MI-service is taking too long to respond thereby slowing down all the services depending on it? We would like to have some timeouts and implement some fallback mechanism.

Following Steps we need to Perform

  • Add Hystrix Dependency

  • Enable Hystrix functaionlity in our EDC-Microservice, by adding @EnableHystrix on our main SpringBoot Class

  • Use @HystrixCommand(fallbackMethod = “miReportFallBackMethod”) to define fallback method if called microservice is down or unreachable

Add Hystrix starter to catalog-service.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
    <version>2.2.10.RELEASE</version>
</dependency>

To enable Circuit Breaker add @@EnableHystrix annotation on catalog-service entry-point class.

@SpringBootApplication 
@EnableHystrix
public class EDCMicroServiceMainApplication {
	
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

 public static void main(String[] args) {
		SpringApplication.run(EDCMicroServiceMainApplication.class, args); 
		System.out.println(" EDC Service... ");  
    }
}

@RestController
public class TestReportController {

	@Autowired
	TestReportRepository repository;
	
	@Autowired
	RestTemplate restTemplate;
	 	 

 
	@GetMapping(value =  "/testReport/mi", produces = "application/json")
       @HystrixCommand(fallbackMethod = "miReportFallBackMethod")
	public ResponseEntity<Object> getAllMIReportsWithHyStrix() {
		try {			
			ResponseEntity<Object> responseEntity =  restTemplate.getForEntity("http://MI-MICROSERVICE/mi/anthology/all", Object.class);
			System.out.println(responseEntity);
			 
			return new ResponseEntity<>(responseEntity, HttpStatus.OK);
		} catch (Exception e) {
			return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
		}
	}
  
	public ResponseEntity<Object> miReportFallBackMethod() {
	try {			
		return new ResponseEntity<>("MI Service is Not Avaialable", HttpStatus.OK);
	     }catch (Exception e) {
		return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
	   }
	}	

}

We have annotated the method from where we are making a REST call with @HystrixCommand(fallbackMethod = “miReportFallBackMethod”) so that if it doesn’t receive the response within the certain time limit the call gets timed out and invoke the configured fallback method.

The fallback method should be defined in the same class and should have the same signature(return type). In the fallback method miReportFallBackMethod() we are setting default behavior depends on what business wants.

I have Stopped MI-MicroService, for checking HyStrix Working

Without Hystrix

With Hystrix

HyStrix Dashboard

We have two ways to configure Hystrix Dashoboard

1.Enable Hystrix Dashboard EDC-MicroService it self.

Add Dashboard Dependency

	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
		<version>2.2.10.RELEASE</version>
	</dependency>

2.Add @EnableHystrixDashboard annotation to SpringBoot main Class

@SpringBootApplication 
@EnableHystrix
@EnableHystrixDashboard
public class EDCMicroServiceMainApplication {
}

Once we add Hystrix starter to EDC-Microservice we can get the circuits status as a stream of events using Actuator endpoint.

http://localhost:8181/actuator/hystrix.stream , assuming catalog-service is running on 8181 port.

2.Separate Server for Connecting Hystrix

Spring Cloud also provides a nice dashboard to monitor the status of Hystrix commands. Create a Spring Boot application with Hystrix Dashboard starter and annotate the main entry-point class with @EnableHystrixDashboard.

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

Now in Hystrix Dashboard home page enter http://localhost:8181/actuator/hystrix.stream as stream URL and give Catalog Service as Title and click on Monitor Stream button.

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