We will add Hystrix to our service consumer microservice and enhance the add service to return a basic response even when Microservice A is down.

We will start with adding Hystrix Starter to the pom.xml file of service consumer microservice. The following snippet shows the dependency details:

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

Next, we would enable Hystrix auto-configuration by adding the @EnableHystrix annotation to the ServiceConsumerApplication class. The following snippet shows the details:

    @SpringBootApplication
    @EnableFeignClients("com.mastering.spring.consumer")
    @EnableHystrix
    @EnableDiscoveryClient
    public class ServiceConsumerApplication {

NumberAdderController exposes a service with request mapping /add. This uses RandomServiceProxy to fetch random numbers. What if this service fails? Hystrix provides a fallback. The following snippet shows how we can add a fallback method to a request mapping. All we need to do is add the @HystrixCommand annotation to the fallbackMethod attribute, defining the name of the fallback method--in this example, getDefaultResponse:

    @HystrixCommand(fallbackMethod = "getDefaultResponse")
    @RequestMapping("/add")
    public Long add() {
      //Logic of add() method 
    }

Next, we define the getDefaultResponse() method with the same return type as the add() method. It returns a default hardcoded value:

    public Long getDefaultResponse() {
      return 10000L;
     }

Let's bring down Microservice A and invoke http://localhost:8100/add. You will get the following response:

    10000

When Microservice A fails, the service consumer microservice handles it gracefully and offers reduced functionality.