This CKAD practice question tests your understanding of application observability and maintenance. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 pod is running but the application inside is not serving traffic. The team runs 'kubectl exec -it <pod> -- curl localhost:8080' and gets 'Connection refused'. 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.
Container logs are full and writing to disk is slow
Why wrong: Would not cause connection refused.
NetworkPolicy is blocking traffic
Why wrong: NetworkPolicy affects external traffic, not localhost.
Application is not listening on port 8080
Connection refused indicates nothing listening on that port.
Liveness probe is failing and restarting the container
Why wrong: If restarting, the pod would show restarts.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Application is not listening on port 8080
The 'Connection refused' error from curl indicates that the TCP connection to port 8080 was actively rejected by the kernel, meaning no process is listening on that port inside the container. This is most commonly caused by the application not starting, crashing before binding, or being configured to listen on a different port (e.g., 3000, 8443). The error is immediate and does not suggest a timeout or network-level block.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Container logs are full and writing to disk is slow
Why it's wrong here
Would not cause connection refused.
NetworkPolicy is blocking traffic
Why it's wrong here
NetworkPolicy affects external traffic, not localhost.
Application is not listening on port 8080
Why this is correct
Connection refused indicates nothing listening on that port.
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.
Liveness probe is failing and restarting the container
Why it's wrong here
If restarting, the pod would show restarts.
Common exam traps
CNCF often tests the distinction between 'Connection refused' (no listener) and 'Connection timed out' (network block) — candidates mistakenly attribute the error to NetworkPolicy or resource issues, but the immediate RST is a definitive sign of a missing socket, not a network filter.
Trap categories for this question
Command / output trap
If restarting, the pod would show restarts.
Detailed technical explanation
When a TCP client receives 'Connection refused', the kernel sends an RST (reset) packet because no socket is bound to the requested port. This is distinct from a timeout (no response) or a connection hang. In Kubernetes, the application inside the container must explicitly bind to 0.0.0.0:8080 or localhost:8080 — if it binds to a different interface (e.g., 127.0.0.1:8080 inside a multi-network pod) or a different port, curl will fail with this exact error. Common causes include misconfigured environment variables (e.g., PORT=3000) or the application crashing before the listen() call.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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
Application Observability and Maintenance — This question tests Application Observability and Maintenance — Read the scenario before looking for a memorised answer..
The correct answer is: Application is not listening on port 8080 — The 'Connection refused' error from curl indicates that the TCP connection to port 8080 was actively rejected by the kernel, meaning no process is listening on that port inside the container. This is most commonly caused by the application not starting, crashing before binding, or being configured to listen on a different port (e.g., 3000, 8443). The error is immediate and does not suggest a timeout or network-level block.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This CKAD 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 CKAD exam.
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