sc-oss.md

Spring Cloud Netflix: Circuit Breaking

• Spring Cloud Netflix: Circuit Breaking
  • Requirements
  • What You Will Learn
  • Exercises
    • Start the config-server, service-registry, and fortune-service
    • Set up greeting-hystrix
    • Set up the greeting-hystrix metric stream
    • Set up hystrix-dashboard

Requirements

Lab Requirements

What You Will Learn

• How to protect your application (greeting-hystrix) from failures or latency with the circuit breaking pattern
• How to publish circuit-breaking metrics from your application (greeting-hystrix)
• How to consume metric streams with the hystrix-dashboard

Exercises

Start the config-server, service-registry, and fortune-service

1. Start the config-server in a terminal window. You may have terminal windows still open from previous labs. They may be reused for this lab.

$ cd $CLOUD_NATIVE_APP_LABS_HOME/config-server
$ mvn clean spring-boot:run

2. Start the service-registry

$ cd $CLOUD_NATIVE_APP_LABS_HOME/service-registry
$ mvn clean spring-boot:run

3. Start the fortune-service

$ cd $CLOUD_NATIVE_APP_LABS_HOME/fortune-service
$ mvn clean spring-boot:run

Set up greeting-hystrix

1. Review the $CLOUD_NATIVE_APP_LABS_HOME/greeting-hystrix/pom.xml file. By adding spring-cloud-starter-hystrix to the classpath this application is eligible to use circuit breakers via Hystrix.

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

2. Review the following file: $CLOUD_NATIVE_APP_LABS_HOME/greeting-hystrix/src/main/java/io/pivotal/GreetingHystrixApplication.java. Note the use of the @EnableCircuitBreaker annotation. This allows the application to create circuit breakers.

@SpringBootApplication
@EnableDiscoveryClient
@EnableCircuitBreaker
public class GreetingHystrixApplication {


    public static void main(String[] args) {
        SpringApplication.run(GreetingHystrixApplication.class, args);
    }

}

3). Review the following file: $CLOUD_NATIVE_APP_LABS_HOME/greeting-hystrix/src/main/java/io/pivotal/fortune/FortuneService.java. Note the use of the @HystrixCommand. This is our circuit breaker. If getFortune() fails, a fallback method defaultFortune will be invoked.

@Service
public class FortuneService {

	Logger logger = LoggerFactory
			.getLogger(FortuneService.class);

	@Autowired
	@LoadBalanced
	private RestTemplate restTemplate;

	@HystrixCommand(fallbackMethod = "defaultFortune")
	public String getFortune() {
    String fortune = restTemplate.getForObject("http://fortune-service", String.class);
		return fortune;
	}

	public String defaultFortune(){
		logger.debug("Default fortune used.");
		return "This fortune is no good. Try another.";
	}



}

4. Open a new terminal window. Start the greeting-hystrix

$ cd $CLOUD_NATIVE_APP_LABS_HOME/greeting-hystrix
$ mvn clean spring-boot:run

5. Refresh the greeting-hystrix / endpoint. You should get fortunes from the fortune-service.

6. Stop the fortune-service. And refresh the greeting-hystrix / endpoint again. The default fortune is given.

7. Restart the fortune-service. And refresh the greeting-hystrix / endpoint again. After some time, fortunes from the fortune-service are back.

What Just Happened?

The circuit breaker tripped because the fortune-service was not available. This insulates the greeting-hystrix application so that our users have a better user experience.

Set up the greeting-hystrix metric stream

Being able to monitor the state of our circuit breakers is highly valuable, but first the greeting-hystrix application must expose the metrics.

This is accomplished by including the actuator dependency in the greeting-hystrix pom.xml.

1. Review the $CLOUD_NATIVE_APP_LABS_HOME/greeting-hystrix/pom.xml file. By adding spring-boot-starter-actuator to the classpath this application will publish metrics at the /hystrix.stream endpoint.

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

2. Browse to http://localhost:8080/hystrix.stream to review the metric stream.

Set up hystrix-dashboard

Consuming the metric stream is difficult to interpret on our own. The metric stream can be visualized with the Hystrix Dashboard.

1. Review the $CLOUD_NATIVE_APP_LABS_HOME/hystrix-dashboard/pom.xml file. By adding spring-cloud-starter-hystrix-dashboard to the classpath this application is exposes a Hystrix Dashboard.

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

2. Review the following file: $CLOUD_NATIVE_APP_LABS_HOME/hystrix-dashboard/src/main/java/io/pivotal/HystrixDashboardApplication.java. Note the use of the @EnableHystrixDashboard annotation. This creates a Hystrix Dashboard.

@SpringBootApplication
@EnableHystrixDashboard
public class HystrixDashboardApplication {

    public static void main(String[] args) {
        SpringApplication.run(HystrixDashboardApplication.class, args);
    }
}

3. Open a new terminal window. Start the hystrix-dashboard

$ cd $CLOUD_NATIVE_APP_LABS_HOME/hystrix-dashboard
$ mvn clean spring-boot:run

4. Open a browser to http://localhost:8686/hystrix

5. Link the hystrix-dashboard to the greeting-hystrix app. Enter http://localhost:8080/hystrix.stream as the stream to monitor.

6. Experiment! Refresh the greeting-hystrix / endpoint several times. Take down the fortune-service app. What does the dashboard do? Review the dashboard doc for an explanation on metrics.