DiscoveryClient seems to fail with null pointer in some instances and not others

[ljramones]

I have used the DiscoveryClient in some instances and it seems to work fine, however in others it throws a NPE for no reason that I can determine. In all cases my spring boot app is annotated with @EnableEurekaClient

There are occasions when if I auto wire the DiscoveryClient such as

  @Autowired
    private DiscoveryClient discoveryClient;

and then later I call it via

 private InstanceInfo findLockManager() {
        InstanceInfo instance = null;
        try {
            instance = discoveryClient.getNextServerFromEureka(LOCK_MANAGER, false);
        } catch (RuntimeException e) {
            logger.error("Failed to find service " + LOCK_MANAGER, e);
            return null;
        }
        return instance;
    }

While running I see this

java.lang.NullPointerException: null
    at com.netflix.discovery.DiscoveryClient$$FastClassBySpringCGLIB$$a84c8cb4.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:708)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:133)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:121)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
    at com.netflix.discovery.DiscoveryClient$$EnhancerBySpringCGLIB$$4ff799f6.getNextServerFromEureka(<generated>)
    at com.cisco.services.rpil.management.NodeStatusManager.findLockManager(NodeStatusManager.java:153)
    at com.cisco.services.rpil.management.NodeStatusManager.setGlobalLock(NodeStatusManager.java:170)
    at com.cisco.services.rpil.management.NodeStatusManager.startup(NodeStatusManager.java:91)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:349)
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(InitDestroyAnnotationBeanPostProcessor.java:300)
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:133)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:407)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1545)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:703)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:109)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:691)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:320)
    at com.cisco.services.rpil.MicroServiceApplication.main(MicroServiceApplication.java:60)

[dsyer]

It looks like NodeStatusManager.startup() is maybe @PostConstruct so you are trying to use the client before it is initialized. The EurekaClientConfiguration initializes the client but only as late as possible (to avoid other race conditions), which means in a Lifecycle.start() method. If you can move your initialization to happen later (lazily or in a SmartLifecycle.start() with order>0) it should have time to get ready before you need it.

[ljramones]

I changed the code to use a SmartLifecycle, put a high value in getPhase() override method and it seems fine now.
This is probably something to put in a FAQ.
Thanks.