KCNA Kubernetes Fundamentals Practice Question
A Service of type ClusterIP has been created, but pods in the same namespace cannot reach it by its DNS name. The Service selector matches the pods. What is a likely cause?
⚠ Common exam trap
Watch out — candidates often assume DNS resolution is automatic and always available, overlooking that the DNS service itself is a critical component that must be running for name-based Service discovery to work.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The kube-dns or CoreDNS pod is not running
The DNS name resolution for a ClusterIP Service relies on the cluster's DNS service (kube-dns or CoreDNS). If the DNS pod is not running, the Service's DNS record (e.g., <service>.<namespace>.svc.cluster.local) cannot be resolved, even if the Service itself is properly configured and the pods match the selector. Without DNS, pods must use the Service's ClusterIP directly, which is not the expected behavior for name-based access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Service YAML does not specify a port
Why it's wrong here
If no port is specified, the Service would not work, but the question implies it is created. Additionally, DNS resolution works regardless of port.
- ✓
The kube-dns or CoreDNS pod is not running
Why this is correct
DNS resolution is provided by CoreDNS; if it is down, DNS names cannot be resolved.
- ✗
The Service is not exposed on a node port
Why it's wrong here
NodePort is for external access; internal DNS does not depend on it.
- ✗
The pods are using an incorrect container runtime
Why it's wrong here
Container runtime does not affect DNS resolution.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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