This CKA practice question tests your understanding of services & networking. 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 a Kubernetes administrator overseeing a multi-tier application in a production cluster. The application consists of a front-end web server (Deployment 'frontend') and a backend API (Deployment 'backend'). The frontend needs to communicate with the backend using the DNS name 'backend-service' within the same namespace 'prod'. Users report intermittent 'Connection Refused' errors when accessing the frontend, which then cannot reach the backend. After checking the backend pods, they are all running and ready. The backend Service is defined as a ClusterIP service with no ports specified in the YAML manifest. What is the most likely cause of the failure?
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 backend Service manifest is missing the 'ports' field, so it has no endpoints.
A ClusterIP Service without a 'ports' field in its manifest will have no port mappings defined, meaning the Service controller cannot create endpoints for it. Even though the backend pods are running and ready, the Service will have no endpoints, so DNS resolution of 'backend-service' will succeed but any connection attempt will result in 'Connection Refused' because there is no target port to forward traffic to.
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 backend Service manifest is missing the 'ports' field, so it has no endpoints.
Why this is correct
Without ports, the Service does not forward traffic, leading to connection refused.
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 backend pods are listening on a different port than expected by the frontend.
Why it's wrong here
That would cause connection timeout, not immediate refusal.
✗
The 'kube-proxy' is not running on the node where the frontend pod is scheduled.
Why it's wrong here
This would affect all services, not just backend.
✗
A NetworkPolicy in the 'prod' namespace is blocking traffic from the frontend to the backend.
Why it's wrong here
NetworkPolicy would drop packets (timeout), not immediately refuse.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a Service will automatically detect pod ports from the pod template, but Kubernetes requires an explicit 'ports' field in the Service manifest to create endpoints.
Detailed technical explanation
How to think about this question
When a Service is created without a 'ports' field, the Kubernetes API server accepts the manifest but the EndpointSlice controller does not generate any endpoints because there is no port to match against the pod's containerPort. The Service's ClusterIP is assigned and DNS resolves correctly, but iptables or IPVS rules generated by kube-proxy will have no valid backend targets, causing TCP SYN packets to be dropped or RST sent back, resulting in 'Connection Refused'. This is a common misconfiguration when using imperative commands like 'kubectl expose' without specifying --port.
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 CKA 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 CKA question in full detail.
Services & Networking — This question tests Services & Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backend Service manifest is missing the 'ports' field, so it has no endpoints. — A ClusterIP Service without a 'ports' field in its manifest will have no port mappings defined, meaning the Service controller cannot create endpoints for it. Even though the backend pods are running and ready, the Service will have no endpoints, so DNS resolution of 'backend-service' will succeed but any connection attempt will result in 'Connection Refused' because there is no target port to forward traffic to.
What should I do if I get this CKA 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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