This KCNA practice question tests your understanding of container orchestration. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 DevOps team notices that a new deployment of a web application is not receiving traffic even though the pods are running. The deployment has a selector matching the pod labels, and a Service of type ClusterIP exists. 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's targetPort does not match the container's containerPort.
The most likely cause is that the Service's targetPort does not match the container's containerPort. In Kubernetes, a Service routes traffic to pods by forwarding packets to the port specified in the Service's `targetPort` field. If this does not match the `containerPort` defined in the pod's container spec, the traffic will be dropped because the kube-proxy will forward packets to a closed port on the pod, resulting in no connectivity even though the pods are running.
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's targetPort does not match the container's containerPort.
Why this is correct
The Service routes traffic to the targetPort, which must match the port the container listens on.
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 pods do not have a readiness probe defined.
Why it's wrong here
Readiness probes affect traffic routing only when pods are not ready, but the pods are running.
✗
The Service type should be NodePort to receive traffic.
Why it's wrong here
ClusterIP is sufficient for internal traffic.
✗
The Service is not exposed via an Ingress.
Why it's wrong here
Ingress is for external HTTP traffic, not required for internal ClusterIP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the Service's `port` (the port the Service listens on) with `targetPort` (the port on the pod), assuming they must match, or they incorrectly attribute the issue to missing readiness probes or Ingress resources.
Detailed technical explanation
How to think about this question
Under the hood, kube-proxy on each node uses iptables or IPVS rules to rewrite the destination IP and port of packets destined for the Service's ClusterIP to the IP and `targetPort` of a selected pod. If the `targetPort` is incorrect, the packet arrives at the pod on a port where no process is listening, causing a TCP RST or connection timeout. In real-world scenarios, this mismatch often occurs when the container image exposes a port (e.g., 8080) but the Service's `targetPort` defaults to the same value as `port` (e.g., 80), leading to silent traffic drops.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this KCNA question in full detail.
Container Orchestration — This question tests Container Orchestration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Service's targetPort does not match the container's containerPort. — The most likely cause is that the Service's targetPort does not match the container's containerPort. In Kubernetes, a Service routes traffic to pods by forwarding packets to the port specified in the Service's `targetPort` field. If this does not match the `containerPort` defined in the pod's container spec, the traffic will be dropped because the kube-proxy will forward packets to a closed port on the pod, resulting in no connectivity even though the pods are running.
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.
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Question Discussion
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