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.
| Reference: | Using Netflix Hystrix annotations with Spring from our JCG partner Biju Kunjummen at the all and sundry blog. |
