CKAD Application Observability and Maintenance Practice Question
This CKAD practice question tests your understanding of application observability and maintenance. 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.
You are debugging a network issue: a pod 'frontend' cannot reach a service 'backend' in the same namespace. The service endpoints are empty. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service selector does not match the labels of any running pod.
B is correct because the most common reason for empty endpoints in a Kubernetes service is that the service's selector does not match the labels of any running pod. The service controller continuously monitors pods and updates the Endpoints object to include only those pods whose labels match the service's selector. If no pods match, the endpoints list remains empty, causing the frontend pod to fail to reach the backend service.
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 pod 'frontend' is not in the same namespace as the service 'backend'.
Why it's wrong here
If in different namespaces, the service would need to be accessed via fully qualified name, but endpoints could still exist.
✓
The service selector does not match the labels of any running pod.
Why this is correct
Endpoints are populated by pods matching the selector; if none match, endpoints remain empty.
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 pod's container port is different from the service port.
Why it's wrong here
Service port mapping works if targetPort matches container port; mismatch would not cause empty endpoints.
✗
The kube-proxy is misconfigured and not updating iptables rules.
Why it's wrong here
This would affect connectivity even if endpoints exist.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the cause of empty endpoints with other networking issues like port mismatches or kube-proxy problems, but the CKAD exam specifically tests the understanding that endpoints are directly tied to label selector matching, not to port configuration or proxy behavior.
Detailed technical explanation
How to think about this question
The Endpoints object is automatically created by the endpoint controller when a service is defined, and it lists the IP addresses and ports of pods that match the service's label selector. If the selector is incorrect or no pods have the matching labels, the Endpoints object will have an empty 'subsets' field. You can verify this with 'kubectl get endpoints <service-name>' and check the pod labels with 'kubectl get pods --show-labels'. In real-world scenarios, this often happens after a deployment update where labels are changed but the service selector is not updated accordingly.
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 CKAD 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKAD question in full detail.
Application Observability and Maintenance — This question tests Application Observability and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The service selector does not match the labels of any running pod. — B is correct because the most common reason for empty endpoints in a Kubernetes service is that the service's selector does not match the labels of any running pod. The service controller continuously monitors pods and updates the Endpoints object to include only those pods whose labels match the service's selector. If no pods match, the endpoints list remains empty, causing the frontend pod to fail to reach the backend service.
What should I do if I get this CKAD 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.
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Question Discussion
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