Service discovery via DNS in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does Kubernetes DNS service discovery work?

In Kubernetes, how does the DNS service discovery mechanism help pods find other services?

A Pods use DNS names that resolve to service cluster IPs, allowing communication without hardcoding IPs.

B Pods communicate only via static IP addresses assigned manually to each pod.

C Pods use environment variables only to discover other services, DNS is not involved.

D Pods must use external DNS servers to resolve service names outside the cluster.

💡 Hint

Think about how pods avoid using fixed IPs and still find services dynamically.

Kubernetes creates DNS entries for services that resolve to their cluster IPs. Pods use these DNS names to communicate without needing fixed IPs.

💻 Command Output

intermediate

Output of DNS lookup inside a pod

What is the output of the following command run inside a pod in Kubernetes?

nslookup my-service.default.svc.cluster.local

A nslookup: can't resolve 'my-service.default.svc.cluster.local'

B

Name: my-service.default.svc.cluster.local
Address: 10.96.0.1

C

Name: my-service
Address: 192.168.1.1

D Error: command not found

💡 Hint

Consider the default cluster IP range and DNS naming conventions.

The DNS name resolves to the cluster IP of the service, typically in the 10.96.0.0/12 range by default.

❓ Configuration

advanced

Correct DNS configuration for a headless service

Which YAML snippet correctly defines a headless service to enable DNS-based service discovery of individual pods?

A

apiVersion: v1
kind: Service
metadata:
  name: my-headless
spec:
  type: LoadBalancer
  selector:
    app: myapp
  ports:
  - port: 80

B

apiVersion: v1
kind: Service
metadata:
  name: my-headless
spec:
  clusterIP: 10.96.0.10
  selector:
    app: myapp
  ports:
  - port: 80

C

apiVersion: v1
kind: Service
metadata:
  name: my-headless
spec:
  clusterIP: None
  selector:
    app: myapp
  ports:
  - port: 80

D

apiVersion: v1
kind: Service
metadata:
  name: my-headless
spec:
  externalName: myapp.example.com
  ports:
  - port: 80

💡 Hint

Headless services have no cluster IP to allow direct pod DNS entries.

Setting clusterIP to None creates a headless service, enabling DNS to return pod IPs directly for service discovery.

❓ Troubleshoot

advanced

Troubleshooting DNS resolution failure in a pod

A pod cannot resolve the DNS name of a service inside the cluster. Which is the most likely cause?

A The pod's container image is missing the nslookup tool.

B The pod is using hostNetwork: true.

C The service has no ports defined in its spec.

D The CoreDNS pods are not running or have crashed.

💡 Hint

DNS resolution depends on a running DNS server inside the cluster.

If CoreDNS pods are down, DNS queries inside the cluster fail, causing resolution errors.

🔀 Workflow

expert

Order the steps to verify DNS-based service discovery in Kubernetes

Put these steps in the correct order to verify DNS-based service discovery inside a Kubernetes cluster.

A 2,4,1,3

B 2,1,4,3

C 1,2,4,3

D 4,2,1,3

💡 Hint

Start by checking cluster components, then run tests inside pods.

First verify the service exists, then confirm DNS server health, next run a pod with DNS tools, and finally query the service DNS name.