docker - minikube how to connect from one pod to another using hostnames?

Question

I am running a cluster in default namespace with all the pods in Running state.

I have an issue, I am trying to telnet from one pod to another pod using the pod hostname 'abcd-7988b76669-lgp8l' but I am not able to connect. although it works if I use pods internal ip. Why does the dns is not resolved?

I looked at

kubectl get po -n kube-system
NAME                          READY   STATUS    RESTARTS   AGE
coredns-6955765f44-5lpfd      1/1     Running   0          12h
coredns-6955765f44-9cvnb      1/1     Running   0          12h

Anybody has any idea how to connect from one pod to another using hostname resolution ?

Answer 1

First of all it is worth mentioning that typically you won't connect to individual Pods using their domain names. One good reason for that is their ephemeral nature. Note that typically you don't create plain Pods but controller such as Deployment which manages your Pods and ensures that specific number of Pods of a certain kind is constantly up and running. Pods may be often deleted and recreated hence you should never rely on their domain names in your applications. Typically you will expose them to another apps e.g. running in other Pods via Service. Although using invididual Pod's domain name is not recommended, it is still possible. You can do it just for fun or learning/experimenting purposes.

As @David already mentioned you would help us much more in providing you a comprehensive answer if you EDIT your question and provide a few important details, showing what you've tried already such as your Pods and Services definitions in yaml format.

Answering literally to your question posted in the title:

minikube how to connect from one pod to another using hostnames?

You won't be able to connect to a Pod using simply its hostname. You can e.g. ping your backend Pods exposed via ClusterIP Service by simply pinging the <service-name> (provided it is in the same namespace as the Pod your pinging from).

Keep in mind however that it doesn't work for Pods - neither Pods names nor their hostnames are resolvable by cluster DNS.

You should be able to connect to an individual Pod using its fully quallified domain name (FQDN) provided you have configured everything properly. Just make sure you didn't overlook any of the steps described here:

Make sure you've created a simple Headless Service which may look like this:

apiVersion: v1
kind: Service
metadata:
  name: default-subdomain
spec:
  selector:
    name: busybox
  clusterIP: None

Make sure that your Pods definitions didn't lack any important details:

apiVersion: v1
kind: Pod
metadata:
  name: busybox1
  labels:
    name: busybox
spec:
  hostname: busybox-1
  subdomain: default-subdomain
  containers:
  - image: busybox:1.28
    command:
      - sleep
      - "3600"
    name: busybox
---
apiVersion: v1
kind: Pod
metadata:
  name: busybox2
  labels:
    name: busybox
spec:
  hostname: busybox-2
  subdomain: default-subdomain
  containers:
  - image: busybox:1.28
    command:
      - sleep
      - "3600"
    name: busybox

Speaking about important details, pay special attention that you correctly defined hostname and subdomain in Pod specification and that labels used by Pods match the labels used by Service's selector.

Once everything is configured properly you will be able to attach to Pod busybox1 and ping Pod busybox2 by using its FQDN like in the example below:

$ kubectl exec -ti busybox1 -- /bin/sh
/ # ping busybox-2.default-subdomain.default.svc.cluster.local
PING busybox-2.default-subdomain.default.svc.cluster.local (10.16.0.109): 56 data bytes
64 bytes from 10.16.0.109: seq=0 ttl=64 time=0.051 ms
64 bytes from 10.16.0.109: seq=1 ttl=64 time=0.082 ms
64 bytes from 10.16.0.109: seq=2 ttl=64 time=0.081 ms

I hope this helps.