Question 645 of 997

Kubernetes Fundamentals →hardMultiple ChoiceObjective-mapped

Troubleshoot Service DNS Resolution

This KCNA practice question tests your understanding of kubernetes fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A developer creates a Service of type ClusterIP in namespace 'default'. They attempt to reach the Service from another pod in the same namespace using the Service name 'my-svc'. The connection fails. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The Service port does not match the container port
Why wrong: If ports don't match, the connection would reach the service but fail at the container; however, the symptom would be connection refused, not DNS failure.
B
The cluster DNS service (CoreDNS) is not running or misconfigured
DNS is required for Service name resolution.
C
The Service type should be NodePort
Why wrong: NodePort is for external access; internal access works with ClusterIP.
D
The Service selector does not match any pod labels
Why wrong: If selectors don't match, the Service has no endpoints, but the connection might still reach an empty set.

Full breakdown with real-world context →

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 cluster DNS service (CoreDNS) is not running or misconfigured

The most likely cause is that the cluster DNS service (CoreDNS) is not running or misconfigured. When a pod attempts to reach a Service by its DNS name (e.g., 'my-svc'), Kubernetes relies on CoreDNS to resolve that name to the ClusterIP. If CoreDNS is down, misconfigured, or the pod's DNS resolver is not pointing to it, the name resolution fails, causing the connection to fail even if the Service itself is correctly configured.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 port does not match the container port
Why it's wrong here
If ports don't match, the connection would reach the service but fail at the container; however, the symptom would be connection refused, not DNS failure.
✓
The cluster DNS service (CoreDNS) is not running or misconfigured
Why this is correct
DNS is required for Service name resolution.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Service type should be NodePort
Why it's wrong here
NodePort is for external access; internal access works with ClusterIP.
✗
The Service selector does not match any pod labels
Why it's wrong here
If selectors don't match, the Service has no endpoints, but the connection might still reach an empty set.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume the issue is with the Service configuration (selector or port) rather than the underlying DNS infrastructure, because they forget that name resolution is a prerequisite for Service discovery within the cluster.

Detailed technical explanation

How to think about this question

CoreDNS runs as a Deployment in the kube-system namespace, typically with a ClusterIP Service itself (kube-dns). Pods are configured to use this DNS service via the /etc/resolv.conf file, which contains a nameserver entry pointing to the kube-dns Service IP. If CoreDNS is not running, DNS queries for Service names will fail with NXDOMAIN or SERVFAIL, causing the pod to be unable to resolve 'my-svc' to an IP address. A real-world scenario is when a cluster is provisioned with a misconfigured network plugin that prevents CoreDNS from starting, or when CoreDNS is accidentally scaled to zero replicas.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the KCNA exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this KCNA question test?

Kubernetes Fundamentals — This question tests Kubernetes Fundamentals — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The cluster DNS service (CoreDNS) is not running or misconfigured — The most likely cause is that the cluster DNS service (CoreDNS) is not running or misconfigured. When a pod attempts to reach a Service by its DNS name (e.g., 'my-svc'), Kubernetes relies on CoreDNS to resolve that name to the ClusterIP. If CoreDNS is down, misconfigured, or the pod's DNS resolver is not pointing to it, the name resolution fails, causing the connection to fail even if the Service itself is correctly configured.

What should I do if I get this KCNA question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

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Same concept, more angles

1 more ways this is tested on KCNA

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A Service of type ClusterIP is not resolving DNS names for pods. The pods are running and can communicate with each other via IP addresses. Which component should be checked first?

hard

A.The kubelet on the node where the pod is running
B.The Service's endpoint slices
C.kube-proxy on the nodes
✓ D.CoreDNS pods in the kube-system namespace

Why D: DNS name resolution for Services in Kubernetes is handled by CoreDNS, which runs as pods in the kube-system namespace. When a ClusterIP Service fails to resolve DNS names but pods can communicate via IP addresses, the issue is almost certainly with the DNS resolver itself, not with network connectivity or Service endpoints. CoreDNS must be checked first to ensure it is running, has correct configuration, and can query the Kubernetes API for Service records.

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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.