nslookup: can't resolve kubernetes.default

Question

I am trying to learn DNS in kubernetes with https://kubernetes.io/docs/tasks/administer-cluster/dns-debugging-resolution/

1. I deployed the busybox

2. kubectl get pods busybox -o wide

   NAME      READY     STATUS    RESTARTS   AGE       IP           NODE
   busybox   1/1       Running   0          16m       10.200.1.5   worker-1
   

3. kubectl exec -ti busybox -- nslookup kubernetes.default

   Server:    10.32.0.10
   Address 1: 10.32.0.10 kube-dns.kube-system.svc.cluster.local
   
   nslookup: can't resolve 'kubernetes.default'
   command terminated with exit code 1
   

4. Do I need to modify the /etc/resolv.conf file of the worker-1 node. currently the /etc/resolv.conf content is below

   nameserver 169.254.169.254
   search c.k8s-project-193906.internal google.internal**
   

5. Also the version of the worker-1 lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic

Please help me figure out which configuration causes the resolve error. Do I need to change resolve.conf file and based on what?

Chardin

Can you please provide some more information on where do you try to do that? Is this somewhere in the Cloud (if yes which one) or on-premise Kubernetes? I can tell it is not a minikube so what tool did you use to deploy the cluster? – Cyclostyle

Answer 1

You have encountered a bug in the latest versions of the busybox docker image. Use the tag busybox:1.28 instead of latest. This bug link is here:

"Nslookup does not work in latest busybox image"
"1.27/1.28 are working , 1.29/1.29.1 are not"

Here it is failing with the busybox:latest tag.

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

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

*** Can't find kubernetes.default: No answer
/ # exit
pod "busybox" deleted

Here's the same command succeeding with the busybox:1.28 tag.

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

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

Uremia

nslookup for my service is working inside a busybox but its not working directly what is the reason?? @David – Lavonnelaw

@DavidW: Thanks, man! I have googled for 2h hours about the error in DNS and found it in busybox. – Suffer

Running just nslookup inside pod terminal and hitting enter output busybox version 1.35. How can change that. I was trying to get DNS service discovery to work in minikube. – Sibilla

Answer 2

try this.

vagrant@kubemaster:~$ cat dnsutils.yaml 

apiVersion: v1
kind: Pod
metadata:
  name: dnsutils
  namespace: default
spec:
  containers:
  - name: dnsutils
    image: gcr.io/kubernetes-e2e-test-images/dnsutils:1.3
    command:
      - sleep
      - "3600"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always

save this in yaml format and run kubectl apply -f <filename>.yaml and then run below command

vagrant@kubemaster:~$ kubectl exec -i -t dnsutils -- nslookup 10-40-0-2.default.pod  | tee nginx-pod

Server:     10.96.0.10
Address:    10.96.0.10#53

Name:   10-40-0-2.default.pod.cluster.local
Address: 10.40.0.2

It should resolve the output and save it in the file.

Clomp