title: nested exception is java.net.UnknownHostException when kubernetes pod start
body: <p>When the kuberentes pod start, give thie error messsage,my app using mybatis and when it start, the app must get the dtd file from mybatis server:</p>
  
  <pre><code>2020-02-12 08:29:22.903 ERROR 6 --- [           main] o.s.boot.SpringApplication               : Application run failed
  org.springframework.beans.factory.BeanDefinitionStoreException: IOException parsing XML document from class path resource [mybatis/mybatis-config.xml]; nested exception is java.net.UnknownHostException: mybatis.org
      at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:415) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE]
  </code></pre>
  
  <p>I am very sure the host is exists,and I have tried to put the xml dtd file on my own static service,and the same error.I know it is maybe a DNS problem.I am using this command to check DNS service status,it give this tips: </p>
  
  <pre><code> [root@ops001 ~]# /opt/k8s/bin/kubectl exec -ti soa-user-service-5c8b744d6d-7p9hr -n dabai-fat -- nslookup kubernetes.default
  nslookup: can't resolve '(null)': Name does not resolve
  
  nslookup: can't resolve 'kubernetes.default': Try again
  command terminated with exit code 1
  </code></pre>
  
  <p>so what's the problem about this? This is the pod works fine <code>/etc/resolve.conf</code>:</p>
  
  <pre><code>nameserver 10.254.0.2
  search dabai-fat.svc.cluster.local svc.cluster.local cluster.local
  options ndots:5
  </code></pre>
  
  <p>I can't access the CoreDNS pods not working.The DNS pod running status:</p>
  
  <pre><code>[root@ops001 ~]# kubectl get pods --namespace=kube-system -l k8s-app=kube-dns
  NAME                      READY   STATUS    RESTARTS   AGE
  coredns-89764d78c-zhnwh   1/1     Running   1          4h4m
  </code></pre>
  
  <p>and this is the pod log output:</p>
  
  <pre><code>.:53
  2020-02-12T07:54:32.194Z [INFO] CoreDNS-1.3.1
  2020-02-12T07:54:32.194Z [INFO] linux/amd64, go1.11.4, 6b56a9c
  CoreDNS-1.3.1
  linux/amd64, go1.11.4, 6b56a9c
  2020-02-12T07:54:32.194Z [INFO] plugin/reload: Running configuration MD5 = 8646128cd34ade07719a0787cce6943e
  </code></pre>