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A DNS address within kubernetes cluster

4/22/2018

I was following this kubernetes tutorial in order to set up a DNS service and connect together two separate kubernetes pods. The one, which should serve as a gateway, is listening on port 80, the other one on port 90.

When I use their Node IP, curl 10.32.0.24 and curl 10.32.0.25:90 I can reach them. Nevertheless I can't figure out, how to access them via my DNS service. What the URL will be?

The Namespace is default and this is the result of kubectl cluster-info: Kubernetes master is running at IP_OF_MY_SERVER:6443 KubeDNS is running at IP_OF_MY_SERVER:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy My deployment.yaml is almost the same as in the tutorial:

apiVersion: v1
kind: Service
metadata:
  name: default-subdomain
spec:
  selector:
    name: busybox
  clusterIP: None
  ports:
  - name: foo # Actually, no port is needed.
    port: 80
    targetPort: 80
---
apiVersion: v1
kind: Pod
metadata:
  name: busybox1
  labels:
    name: busybox
spec:
  hostname: busybox-1
  subdomain: default-subdomain
  containers:
  - image: time-provider
    name: busybox
---
apiVersion: v1
kind: Pod
metadata:
  name: busybox2
  labels:
    name: busybox
spec:
  hostname: busybox-2
  subdomain: default-subdomain
  containers:
  - image:  gateway
    name: busybox

-- Martin Dvoracek

cluster-computing

dns

kubernetes

1 Answer

4/23/2018

The Kubernetes DNS service works inside a cluster and provide DNS names for pods, not for external services.

Here is an extract from the instruction you used:

Every Service defined in the cluster (including the DNS server itself) is assigned a DNS name. By default, a client Pod’s DNS search list will include the Pod’s own namespace and the cluster’s default domain. This is best illustrated by example:
Assume a Service named foo in the Kubernetes namespace bar. A Pod running in namespace bar can look up this service by simply doing a DNS query for foo. A Pod running in namespace quux can look up this service by doing a DNS query for foo.bar.

So, the DNS names of your resources inside a cluster exist only in it.

You call to the service from the external network by NodeIPs : curl 10.32.0.24 and curl 10.32.0.25:90. And that is a correct way. If you want to use a DNS names to connect to the cluster from outside, you should use any other DNS service to point names to your cluster nodes or LoadBalancer.

I recommend you to use Service object to expose your application. Here is a some articles about it: ways to connect, use a Service to access applications.

-- Anton Kostenko

Source: StackOverflow

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A DNS address within kubernetes cluster

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