Circuit Breakers

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 config-server
$ mvn spring-boot:run

Start the service-registry

$ cd service-registry
$ mvn spring-boot:run

Start the fortune-service

$ cd fortune-service
$ mvn spring-boot:run

Review the greeting-hystrix project’s pom.xml file. By adding spring-cloud-services-starter-circuit-breaker to the classpath this application is eligible to use circuit breakers via Hystrix.

<dependency>
	<groupId>io.pivotal.spring.cloud</groupId>
	<artifactId>spring-cloud-services-starter-circuit-breaker</artifactId>
</dependency>

Review the class GreetingHystrixApplication.java. Note the use of the @EnableCircuitBreaker annotation. This allows the application to create circuit breakers. Note also how we again configure our RestTemplate bean to be load-balanced.

package io.pivotal;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableDiscoveryClient
@EnableCircuitBreaker
public class GreetingHystrixApplication {

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

    @LoadBalanced
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

Review the class file 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.

package io.pivotal.fortune;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class FortuneService {

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

  private final RestTemplate restTemplate;

  public FortuneService(RestTemplate restTemplate) {
    this.restTemplate = restTemplate;
  }

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

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

}

Open a new terminal window, and launch greeting-hystrix:

$ cd greeting-hystrix
$ mvn spring-boot:run

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

Stop the fortune-service. Now refresh the greeting-hystrix root endpoint again. The default fortune is returned.

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

Review the 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>

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

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

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

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

package io.pivotal;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;

@SpringBootApplication
@EnableHystrixDashboard
public class HystrixDashboardApplication {

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

Open a new terminal window. Start the hystrix-dashboard

$ cd hystrix-dashboard
$ mvn spring-boot:run

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

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

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