This CKAD practice question tests your understanding of services and networking. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 platform engineer managing a Kubernetes cluster version 1.28. A development team has deployed a microservice application called 'order-processor' in the 'prod' namespace. The application consists of a frontend Pod 'frontend' and a backend Pod 'backend', each with a single container. The frontend needs to communicate with the backend using a headless Service named 'backend-svc' that selects Pods with label 'app:backend'. The backend Pods are expected to scale horizontally, and the frontend uses a DNS lookup to discover all backend Pod IPs for client-side load balancing. However, after deploying, the frontend is unable to resolve 'backend-svc' to any IP addresses. The backend Pod is running and has the correct label 'app:backend'. The Service 'backend-svc' is defined as a ClusterIP with clusterIP: None. The frontend container has the 'default' DNS policy. 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 Pod does not have a readiness probe defined, so it is not considered ready and not added to DNS records.
Option C is correct because a headless Service (clusterIP: None) creates DNS A/AAAA records only for Pods that are in the Ready state. Without a readiness probe defined on the backend Pod, Kubernetes considers the Pod not ready, so it is excluded from the DNS records. The frontend's DNS lookup of 'backend-svc' therefore returns no IP addresses, causing the resolution failure.
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 headless Service must have the 'publishNotReadyAddresses: true' field to include not-ready Pods.
Why it's wrong here
publishNotReadyAddresses exists but is not the only way; readiness probes must pass by default.
✗
The Service and frontend are in different namespaces; the DNS name must be fully qualified.
Why it's wrong here
The stem says both are in 'prod' namespace.
✓
The backend Pod does not have a readiness probe defined, so it is not considered ready and not added to DNS records.
Why this is correct
Default behavior: only ready Pods are published in headless Service DNS records.
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 frontend Pod's DNS policy is set to 'None' which disables DNS resolution.
Why it's wrong here
The stem states the frontend has default DNS policy, not None.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a headless Service always returns all matching Pod IPs regardless of readiness, but Kubernetes only publishes ready Pods to DNS unless explicitly configured otherwise.
Detailed technical explanation
How to think about this question
Under the hood, the kube-dns or CoreDNS component watches EndpointSlices (or Endpoints) and only creates DNS records for Pods that satisfy the readiness condition. For headless Services, the DNS response includes all ready Pod IPs, enabling client-side load balancing. A real-world scenario where this matters is when a Pod starts but takes time to become ready (e.g., loading data); without a readiness probe, the Pod is never added to DNS, breaking service discovery for clients that rely on it.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKAD question in full detail.
Services and Networking — This question tests Services and Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backend Pod does not have a readiness probe defined, so it is not considered ready and not added to DNS records. — Option C is correct because a headless Service (clusterIP: None) creates DNS A/AAAA records only for Pods that are in the Ready state. Without a readiness probe defined on the backend Pod, Kubernetes considers the Pod not ready, so it is excluded from the DNS records. The frontend's DNS lookup of 'backend-svc' therefore returns no IP addresses, causing the resolution failure.
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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