K
Q

how to get SRV DNS address for statefulset headless service

5/13/2019

Issue in dns lookup for statefulsets srv records

My yaml file

kind: List
apiVersion: v1
items:
- apiVersion: v1
  kind: Service
  metadata:
    name: sfs-svc
    labels:
      app: sfs-app
  spec:
    ports:
    - port: 80
      name: web
    clusterIP: None
    selector:
      app: sfs-app
- apiVersion: apps/v1
  kind: StatefulSet
  metadata:
    name: web
  spec:
    selector:
      matchLabels:
        app: sfs-app # has to match .spec.template.metadata.labels
    serviceName: "sfs-svc"
    replicas: 3 
    template:
      metadata:
        labels:
          app: sfs-app # has to match .spec.selector.matchLabels
      spec:
        terminationGracePeriodSeconds: 10
        containers:
        - name: test-container
          image: nginx
          imagePullPolicy: IfNotPresent
          command: [ "sh", "-c"]
          args:
          - while true; do
              printenv MY_NODE_NAME MY_POD_NAME MY_POD_NAMESPACE >> /var/sl/output.txt;
              printenv MY_POD_IP >> /var/sl/output.txt;
              date >> var/sl/output.txt; 
              cat /var/sl/output.txt;
              sleep 999999;
            done;
          env:
            - name: MY_NODE_NAME
              valueFrom:
                fieldRef:
                  fieldPath: spec.nodeName
            - name: MY_POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
            - name: MY_POD_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
            - name: MY_POD_IP
              valueFrom:
                fieldRef:
                  fieldPath: status.podIP
          volumeMounts:
          - name: www
            mountPath: /var/sl
    volumeClaimTemplates:
    - metadata:
        name: www
      spec:
        accessModes: [ "ReadWriteOnce" ]
        #storageClassName: classNameIfAny
        resources:
          requests:
            storage: 1Mi

$ Kubectl cluster-info

Kubernetes master is running at https://192.168.99.100:8443 KubeDNS is running at https://192.168.99.100:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

$ kubectl version

Client Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.3", GitCommit:"721bfa751924da8d1680787490c54b9179b1fed0", GitTreeState:"clean", BuildDate:"2019-02-01T20:08:12Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"} Server Version: version.Info{Major:"1", Minor:"14", GitVersion:"v1.14.1", GitCommit:"b7394102d6ef778017f2ca4046abbaa23b88c290", GitTreeState:"clean", BuildDate:"2019-04-08T17:02:58Z", GoVersion:"go1.12.1", Compiler:"gc", Platform:"linux/amd64"}

$ kubectl get po,svc,statefulset

> NAME        READY   STATUS    RESTARTS   AGE
> pod/web-0   1/1     Running   0          45m
> pod/web-1   1/1     Running   0          45m
> pod/web-2   1/1     Running   0          45m
> 
> NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
> service/kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   46m
> service/sfs-svc      ClusterIP   None         <none>        80/TCP    45m
> 
> NAME                   READY   AGE
> statefulset.apps/web   3/3     45m
>

PROBLEM: I am not getting DNS address for statefulset headless service

When I try $ nslookup sfs-svc.default.svc.cluster.local

> Server:       127.0.0.53
> Address:  127.0.0.53#53
> 
**> ** server can't find sfs-svc.default.svc.cluster.local: SERVFAIL**
>
-- A-P
kube-dns
kubernetes
kubernetes-statefulset
minikube
srv

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1 Answer

5/19/2019

My first guess is, you are running nslookup from localhost instead of from inside of a pod.

I tried the yaml and I can only regenerate this problem when I run nslookup sfs-svc.default.svc.cluster.local from localhost.

Anyway, To check the DNS entries of a Service, run nslookup from inside of a pod. Here is an example,

~ $ kubectl run -it --rm --restart=Never dnsutils2 --image=tutum/dnsutils  --command -- bash

root@dnsutils2:/# nslookup sfs-svc.default.svc.cluster.local
Server:     10.96.0.10
Address:    10.96.0.10#53

Name:   sfs-svc.default.svc.cluster.local
Address: 172.17.0.6
Name:   sfs-svc.default.svc.cluster.local
Address: 172.17.0.5
Name:   sfs-svc.default.svc.cluster.local
Address: 172.17.0.4

root@dnsutils2:/# exit
-- Abdullah Al Maruf - Tuhin
Source: StackOverflow