Not able to nslookup kubernetes.default

Question

I have kubernetes cluster running on Ubuntu 16.04. When I run nslookup kubernetes.default on master it shows below:

Server:     192.168.88.21
Address:    192.168.88.21#53

** server can't find kubernetes.default: NXDOMAIN

Below is the content of /etc/resolv.conf

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 192.168.88.21
nameserver 127.0.1.1
search VISDWK.local

Using kubernetes version

kubeadm version: &version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.1", GitCommit:"eec55b9ba98609a46fee712359c7b5b365bdd920", GitTreeState:"clean", BuildDate:"2018-12-13T10:36:44Z", GoVersion:"go1.11.2", Compiler:"gc", Platform:"linux/amd64"}

Using weave for networking and installed using:

kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"

coredns pods are running fine:

coredns-86c58d9df4-42xqc               1/1     Running   8         1d6h
coredns-86c58d9df4-p6d98               1/1     Running   7         1d1h

Below are the logs of coredns-86c58d9df4-42xqc

.:53 2019-02-08T08:40:10.038Z [INFO] CoreDNS-1.2.6 2019-02-08T08:40:10.039Z [INFO] linux/amd64, go1.11.2, 756749c CoreDNS-1.2.6 linux/amd64, go1.11.2, 756749c [INFO] plugin/reload: Running configuration MD5 = f65c4821c8a9b7b5eb30fa4fbc167769 t

Can anyone please help me debug this issue. Please help. Thanks.

Nobukonoby

Answer 1

something wrong with busybox image. it works but am getting some errors after the nslookup command is run

[node1 ~]$ kubectl run busybox1 --image busybox --restart=Never --rm -it -- sh
If you don't see a command prompt, try pressing enter.
/ # nslookup kubernetes
Server:         10.96.0.10
Address:        10.96.0.10:53

Name:   kubernetes.default.svc.cluster.local
Address: 10.96.0.1

*** Can't find kubernetes.svc.cluster.local: No answer
*** Can't find kubernetes.cluster.local: No answer
*** Can't find kubernetes.default.svc.cluster.local: No answer
*** Can't find kubernetes.svc.cluster.local: No answer
*** Can't find kubernetes.cluster.local: No answer
/ # exit
pod "busybox1" deleted
[node1 ~]$

try with below image. it works perfectly. other versions are throwing some errors

busybox:1.28

[node1 ~]$ kubectl run busybox1 --image busybox:1.28 --restart=Never --rm -it -- sh
If you don't see a command prompt, try pressing enter.
/ # nslookup kubernetes
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      kubernetes
Address 1: 10.96.0.1 kubernetes.default.svc.cluster.local
/ # exit
pod "busybox1" deleted

Test the api server from master

[node1 ~]$ kubectl get svc|grep kubernetes
kubernetes      ClusterIP      10.96.0.1      <none>        443/TCP          2h
[node1 ~]$
[node1 ~]$ curl -k https://10.96.0.1/version
{
  "major": "1",
  "minor": "11",
  "gitVersion": "v1.11.7",
  "gitCommit": "65ecaf0671341311ce6aea0edab46ee69f65d59e",
  "gitTreeState": "clean",
  "buildDate": "2019-01-24T19:22:45Z",
  "goVersion": "go1.10.7",
  "compiler": "gc",
  "platform": "linux/amd64"
}[node1 ~]$

Renewal

Sorry I didn't get you. What is the purpose of busybox in it. I am not using busybox – Nobukonoby

you wanted to test nslookup to kubernetes.default. using busybox:1.28 you can check that – Renewal

Okay I got the proper response of nslookup from busybox. Does that mean coredns is working fine.? – Nobukonoby

you should get the output that is shown above for busybox:1.28. Then your cluster is working well – Renewal

Yes I have got the same output as yours. But can you tell me why nslookup wasnt responding on master.? Thank you. – Nobukonoby

check my update above to see how to test api server connection from master server – Renewal

Thanks, one last question, I did this curl on one of the pod and got the proper response so does that mean that the pod and its networking is running fine in cluster.? – Nobukonoby

you are good. But you should also deploy one sample web application to check application and its connectivity to backend database pod. this is to make sure that your cluster is configured correctly – Renewal

nslookup for my service is working fine inside a busybox but its not working directly what is the reason?? @Ekambaram(i checked it using this answer #52109539) – Swartz