Kubernetes DNS name for static Pod's-CodePudding

I dig everywhere to see why we don't have DNS resolution for static pods and couldn't find a right answer. Most basic stuff and couldn't find appealing answer.

Like you create a static pod, exec into it, do a "nslookup pod-name" or like "nslookup 10-44-0-7.default.pod.cluster.local", I know the second one is for Deployment and DaemonSet which creates A record, why not for static pods because they are ephemeral, in that way Deployment also is. Please tell me if it is possible and how we enable it.

My testing for the failed queries, all are static pods created with "kubectl run busybox-2 --image=busybox --command sleep 1d"

Used this as syntax:

In general a pod has the following DNS resolution: pod-ip-address.my-namespace.pod.cluster-domain.example.

vagrant@kubemaster:~$ kubectl get pods -n default -o wide
NAME                          READY   STATUS    RESTARTS       AGE    IP          NODE         NOMINATED NODE   READINESS GATES
busybox-1                     1/1     Running   0              135m   10.36.0.6   kubenode02   <none>           <none>
busybox-2                     1/1     Running   0              134m   10.44.0.7   kubenode01   <none>           <none>
busybox-sleep                 1/1     Running   19 (24h ago)   23d    10.44.0.3   kubenode01   <none>           <none>


/ # cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local Dlink
options ndots:5


/ # nslookup 10-44-0-7.default.pod.cluster.local
Server:         10.96.0.10
Address:        10.96.0.10:53

Name:   10-44-0-7.default.pod.cluster.local
Address: 10.44.0.7

*** Can't find 10-44-0-7.default.pod.cluster.local: No answer

/ # nslookup 10-44-0-6.default.pod.cluster.local
Server:         10.96.0.10
Address:        10.96.0.10:53


*** Can't find 10-44-0-6.default.pod.cluster.local: No answer

Appreciate the help.

CodePudding user response：

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Katacoda Play with Kubernetes Your cluster must be running the CoreDNS add-on. Migrating to CoreDNS explains how to use kubeadm to migrate from kube-dns.

Your Kubernetes server must be at or later than version v1.12. To check the version, enter kubectl version.

CodePudding user response：

DNS Lookup & Reverse lookups does not work for pods/podIPs (By Design!).
Why ? I also had the similar question , After spending a lot of time exploring following are reasons that convinced me :

Pods & and its IPs are ephemeral. even static pods when they get restarted(recreated) they might end up getting a different IP Address.
It will be huge overload on coredns/any dns server to keep a track of ever changing POD IP Addresses.
Due to above reasons It is recommended to access the POD through a service because service will have a constant IP irrespective of how the endpoint IPS have changed. for services DNS lookups & reverse loookups work fine.