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Using Netflix Hystrix Annotations with Spring

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Using Netflix Hystrix Annotations with Spring

My objective here is to recreate a similar set-up in a smaller unit test mode.

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I can't think of a better way to describe a specific feature of Netflix Hystrix library than by quoting from its home page:

Latency and Fault Tolerance by:
Stop cascading failures. Fallbacks and graceful degradation. Fail fast and rapid recovery.

Thread and semaphore isolation with circuit breakers.


I saw a sample demonstrated by Josh Long(@starbuxman) which makes use of Hystrix integrated with Spring - the specific code is here. The sample makes use of annotations to hystrix enable a service class.

My objective here is to recreate a similar set-up in a smaller unit test mode. With that in mind, consider the following interface which is going to be made fault tolerant using Hystrix library:

package hystrixtest;

public interface RemoteCallService {

    String call(String request) throws Exception;

}

And a dummy implementation for it. The dummy implementation delegates to a mock implementation which in-turn fails the first two times it is called and succeeds with the third call:

package hystrixtest;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;

import static org.mockito.Mockito.*;


public class DummyRemoteCallService implements RemoteCallService {

    private RemoteCallService mockedDelegate;

    public DummyRemoteCallService() {
        try {
            mockedDelegate = mock(RemoteCallService.class);
            when(mockedDelegate.call(anyString()))
                    .thenThrow(new RuntimeException("Deliberately throwing an exception 1"))
                    .thenThrow(new RuntimeException("Deliberately throwing an exception 2"))
                    .thenAnswer(new Answer<String>() {
                        @Override
                        public String answer(InvocationOnMock invocationOnMock) throws Throwable {
                            return (String) invocationOnMock.getArguments()[0];
                        }
                    });
        }catch(Exception e) {
            throw new IllegalStateException(e);
        }
    }

    @Override
    @HystrixCommand(fallbackMethod = "fallBackCall")
    public String call(String request) throws Exception {
        return this.mockedDelegate.call(request);
    }

    public String fallBackCall(String request) {
        return "FALLBACK: " + request;
    }
}

The remote call has been annotated with the @Hystrixcommand annotation with a basic configuration to fall back to a "fallBackCall" method in case of a failed remote call.

Now, as you can imagine, there has to be something in the Hystrix library which should intercept calls annotated with @HystrixCommand annotation and makes it fault tolerant. This is a working test which wraps the necessary infrastructure together - in essence, Hystrix library provides a companion AOP based library that intercepts the calls. I have used Spring testing support here to bootstrap the AOP infrastructure, to create the HystrixCommandAspect as a bean, the call goes to the "fallBackCall" for the first two failed calls and succeeds the third time around:

package hystrixtest;

import com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;


@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TestRemoteCallServiceHystrix {

    @Autowired
    private RemoteCallService remoteCallService ;

    @Test
    public void testRemoteCall() throws Exception{
        assertThat(this.remoteCallService.call("test"), is("FALLBACK: test"));
        assertThat(this.remoteCallService.call("test"), is("FALLBACK: test"));
        assertThat(this.remoteCallService.call("test"), is("test"));
    }

    @Configuration
    @EnableAspectJAutoProxy
    public static class SpringConfig {

        @Bean
        public HystrixCommandAspect hystrixCommandAspect() {
            return new HystrixCommandAspect();
        }

        @Bean
        public RemoteCallService remoteCallService() {
            return new DummyRemoteCallService();
        }
    }
}

Spring-Cloud provides an easier way to configure the Netflix libraries for Spring-Boot based projects and if I were to use this library the test would transform to this, a bunch of configuration is now commented out with the help of Spring-Boot:

package hystrixtest;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;


@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration
public class TestRemoteCallServiceHystrix {

    @Autowired
    private RemoteCallService remoteCallService;

    @Test
    public void testRemoteCall() throws Exception {
        assertThat(this.remoteCallService.call("test"), is("FALLBACK: test"));
        assertThat(this.remoteCallService.call("test"), is("FALLBACK: test"));
        assertThat(this.remoteCallService.call("test"), is("test"));
    }

    @Configuration
    @EnableAutoConfiguration
//    @EnableAspectJAutoProxy
    @EnableHystrix
    public static class SpringConfig {

//        @Bean
//        public HystrixCommandAspect hystrixCommandAspect() {
//            return new HystrixCommandAspect();
//        }

        @Bean
        public RemoteCallService remoteCallService() {
            return new DummyRemoteCallService();
        }
    }
}
If you are interested in exploring this sample further,  here is the  github repo with the working tests.

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