Question 147 of 997

Kubernetes Fundamentals →hardMultiple ChoiceObjective-mapped

Troubleshoot Stuck Deployment Rollout Due to Image Pull Issues

This KCNA practice question tests your understanding of kubernetes fundamentals. 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 have a Deployment with image: myapp:v1. You update the image to myapp:v2 using 'kubectl set image deployment/myapp myapp=myapp:v2'. The rollout status shows 'Waiting for rollout to finish: 0 out of 3 new replicas have been updated...'. What is the most likely cause of this behavior?

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.

A
The command syntax is incorrect; you should use 'kubectl set image deployment/myapp myapp:v2'
Why wrong: The syntax 'kubectl set image deployment/myapp myapp=myapp:v2' is correct.
B
The new Pods are crashing due to a missing command
Why wrong: Crashing Pods would cause CrashLoopBackOff, but the rollout would still attempt to update replicas; however, the specific message '0 out of 3 new replicas have been updated' suggests the new Pods are not being created.
C
The Deployment's update strategy is set to 'Recreate'
Why wrong: With 'Recreate', old Pods are terminated before new ones are created, so the rollout should progress.
D
The new image myapp:v2 does not exist or cannot be pulled from the registry
If the image cannot be pulled, the new Pods will remain in ImagePullBackOff, preventing them from being counted as updated.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The new image myapp:v2 does not exist or cannot be pulled from the registry

Option D is correct because the rollout is stuck waiting for new replicas to become ready, which typically happens when the container image cannot be pulled. The message '0 out of 3 new replicas have been updated' indicates that the ReplicaSet is attempting to create Pods with the new image, but the Pods are failing to start. The most common cause is that the image tag 'myapp:v2' does not exist in the registry or cannot be accessed due to authentication or network issues, preventing the kubelet from pulling it.

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 command syntax is incorrect; you should use 'kubectl set image deployment/myapp myapp:v2'
Why it's wrong here
The syntax 'kubectl set image deployment/myapp myapp=myapp:v2' is correct.
✗
The new Pods are crashing due to a missing command
Why it's wrong here
Crashing Pods would cause CrashLoopBackOff, but the rollout would still attempt to update replicas; however, the specific message '0 out of 3 new replicas have been updated' suggests the new Pods are not being created.
✗
The Deployment's update strategy is set to 'Recreate'
Why it's wrong here
With 'Recreate', old Pods are terminated before new ones are created, so the rollout should progress.
✓
The new image myapp:v2 does not exist or cannot be pulled from the registry
Why this is correct
If the image cannot be pulled, the new Pods will remain in ImagePullBackOff, preventing them from being counted as updated.
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.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume a syntax error (Option A) or a Pod crash (Option B) when the real issue is a missing or inaccessible image, which is a common cause of stuck rollouts in Kubernetes.

Detailed technical explanation

How to think about this question

Under the hood, when you update a Deployment's image, the Deployment controller creates a new ReplicaSet and scales it up while scaling down the old one. The kubelet on each node attempts to pull the image from the registry; if the image does not exist or the pull fails (e.g., due to ImagePullBackOff), the Pod remains in 'Pending' or 'ErrImagePull' state, and the ReplicaSet reports zero ready replicas. The rollout progress message persists until the image pull succeeds or the rollout is manually aborted. In real-world scenarios, this often occurs when a CI/CD pipeline pushes a tag that doesn't match the registry or when private registry credentials are missing.

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.

What to study next

Got this wrong? Here's your next step.

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

Questions learners often ask

What does this KCNA question test?

Kubernetes Fundamentals — This question tests Kubernetes Fundamentals — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The new image myapp:v2 does not exist or cannot be pulled from the registry — Option D is correct because the rollout is stuck waiting for new replicas to become ready, which typically happens when the container image cannot be pulled. The message '0 out of 3 new replicas have been updated' indicates that the ReplicaSet is attempting to create Pods with the new image, but the Pods are failing to start. The most common cause is that the image tag 'myapp:v2' does not exist in the registry or cannot be accessed due to authentication or network issues, preventing the kubelet from pulling it.

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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