KCNA Kubernetes Fundamentals Practice Question
A user reports that their application's DNS resolution is failing for a Service named 'my-service' in the same namespace. They are able to reach the Service by its cluster IP. Which of the following is the most likely cause?
⚠ Common exam trap
CNCF often tests the distinction between DNS resolution and Service reachability, trapping candidates who assume that a DNS failure must be caused by the application's DNS policy rather than the cluster DNS service itself.
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 CoreDNS pod is not running or misconfigured
DNS resolution for a Service in the same namespace relies on CoreDNS, which is the cluster DNS provider in Kubernetes. If CoreDNS is not running or misconfigured, DNS queries for the Service name (e.g., 'my-service') will fail, even though the Service is reachable via its cluster IP. The user's ability to reach the Service by IP confirms that kube-proxy and networking are functional, isolating the issue to DNS resolution.
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 application container is using an incorrect DNS policy
Why it's wrong here
While an incorrect DNS policy (e.g., dnsPolicy: None) could cause issues, the most likely cause is CoreDNS not running, as the user can reach the Service by IP.
- ✗
The kube-proxy is misconfigured on the node
Why it's wrong here
kube-proxy handles network rules for Service IPs, not DNS resolution. DNS is handled by CoreDNS.
- ✓
The CoreDNS pod is not running or misconfigured
Why this is correct
CoreDNS is responsible for DNS resolution for Services. If CoreDNS is down or misconfigured, DNS queries for Services will fail.
- ✗
The Service is of type ExternalName
Why it's wrong here
ExternalName services return a CNAME record; if the external name is resolvable, DNS would work. This is unlikely to cause DNS failure within the cluster.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This KCNA practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the KCNA exam.