Question 660 of 997

Kubernetes Fundamentals →hardMultiple ChoiceObjective-mapped

Deployment Rollout Paused: When Readiness Probes Fail

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 deploy a new version of your application by updating the container image in the Deployment manifest. The rollout seems to be progressing, but after a few minutes you notice that the new Pods are failing and the old Pods are still running. What is the most likely reason?

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 Deployment was created with 'kubectl create deployment' instead of 'kubectl apply'
Why wrong: Both commands can create deployments; the issue is not about the command used.
B
The new Pods are failing readiness probes, so the Deployment pauses the rollout and keeps the old replicas
If readiness probes fail, the new Pods are not considered ready, and the Deployment controller will not continue the rollout, preserving the old replicas.
C
The new Pods are not receiving traffic because the Service selector doesn't match
Why wrong: A Service selector mismatch would affect traffic routing, but the rollout itself would not fail; the new Pods would still be created.
D
The Deployment's update strategy is set to 'Recreate'
Why wrong: A Recreate strategy would delete all old Pods before creating new ones, so old Pods would not remain running.

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 Pods are failing readiness probes, so the Deployment pauses the rollout and keeps the old replicas

When a new Pod fails its readiness probe, the Deployment controller considers the new ReplicaSet unhealthy and pauses the rollout. The controller keeps the old ReplicaSet running to maintain the desired number of available replicas, preventing traffic disruption until the new Pods pass their probes or the rollout is manually resumed.

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 Deployment was created with 'kubectl create deployment' instead of 'kubectl apply'
Why it's wrong here
Both commands can create deployments; the issue is not about the command used.
✓
The new Pods are failing readiness probes, so the Deployment pauses the rollout and keeps the old replicas
Why this is correct
If readiness probes fail, the new Pods are not considered ready, and the Deployment controller will not continue the rollout, preserving the old replicas.
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 new Pods are not receiving traffic because the Service selector doesn't match
Why it's wrong here
A Service selector mismatch would affect traffic routing, but the rollout itself would not fail; the new Pods would still be created.
✗
The Deployment's update strategy is set to 'Recreate'
Why it's wrong here
A Recreate strategy would delete all old Pods before creating new ones, so old Pods would not remain running.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The CNCF Kubernetes exam often tests the distinction between liveness and readiness probes; candidates mistakenly think a failing liveness probe causes the same behavior, but only readiness probe failures pause a rollout while liveness failures restart the Pod without affecting the rollout progress.

Trap categories for this question

Command / output trap
Both commands can create deployments; the issue is not about the command used.

Detailed technical explanation

How to think about this question

The Deployment controller uses a rolling update strategy by default (maxSurge=25%, maxUnavailable=25%). When a new ReplicaSet's Pods fail readiness probes, the controller sets the rollout status to 'Progressing' with a condition 'ReplicaFailure' and does not scale down the old ReplicaSet. This behavior is governed by the Deployment's progressDeadlineSeconds (default 600 seconds) and the 'kubectl rollout status' command will show the rollout as stuck. In real-world scenarios, this often happens when a new application version has a bug that prevents it from responding to HTTP health checks on the configured readiness probe endpoint.

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 Pods are failing readiness probes, so the Deployment pauses the rollout and keeps the old replicas — When a new Pod fails its readiness probe, the Deployment controller considers the new ReplicaSet unhealthy and pauses the rollout. The controller keeps the old ReplicaSet running to maintain the desired number of available replicas, preventing traffic disruption until the new Pods pass their probes or the rollout is manually resumed.

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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