K
Q

How to resolve the hostname between the pods in the kubernetes cluster?

9/4/2020

I am creating two pods with a custom docker image(ubuntu is the base image). I am trying to ping the pods from their terminal. I am able to reach it using the IP address but not the hostname. How to achieve without manually adding /etc/hosts in the pods?

Note: I am not running any services in the node. I am basically trying to setup slurm using this.

Pod Manifest File: 

apiVersion: v1
kind: Pod
metadata:
  name: slurmctld
  labels:
    app: slurm
spec:
  nodeName: docker-desktop
  hostname: slurmctld
  containers:
    - name: slurmctld
      image: slurmcontroller
      imagePullPolicy: Always
      ports:
        - containerPort: 6817
      resources:
        requests:
          memory: "1000Mi"
          cpu: "1000m"
        limits:
          memory: "1500Mi"
          cpu: "1500m"  
      command: [ "/bin/bash", "-c", "--" ]
      args: [ "while true; do sleep 30; done;" ]
---
apiVersion: v1
kind: Pod
metadata:
  name: worker1
  labels:
    app: slurm
spec:
  nodeName: docker-desktop
  hostname: worker1        
  containers:
    - name: worker1
      image: slurmworker
      imagePullPolicy: Always
      ports:
        - containerPort: 6818
      resources:
        requests:
          memory: "1000Mi"
          cpu: "1000m"
        limits:
          memory: "1500Mi"
          cpu: "1500m"    
      command: [ "/bin/bash", "-c", "--" ]
      args: [ "while true; do sleep 30; done;" ]
-- Akhil
dns
docker
kube-dns
kubernetes
slurm

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1 Answer

9/4/2020

From the docs here

In general a pod has the following DNS resolution:

pod-ip-address.my-namespace.pod.cluster-domain.example.

For example, if a pod in the default namespace has the IP address 172.17.0.3, and the domain name for your cluster is cluster.local, then the Pod has a DNS name:

172-17-0-3.default.pod.cluster.local.

Any pods created by a Deployment or DaemonSet exposed by a Service have the following DNS resolution available:

pod-ip-address.deployment-name.my-namespace.svc.cluster-domain.example

If you don't like to deal with ever changing IP of a pod then you need to create service to expose the pods using DNS hostnames. Below is an example of service to expose the slurmctld pod.

apiVersion: v1
kind: Service
metadata:
  name: slurmctld-service
spec:
  selector:
    app: slurm
  ports:
    - protocol: TCP
      port: 80
      targetPort: 6817

Assuming you are doing these on default namespace You should now be able to access it via slurmctld-service.default.svc.cluster.local

-- Arghya Sadhu
Source: StackOverflow