The answer is that the worker node has not been cordoned before running the upgrade. The `kubeadm upgrade node` command fails with a 'node is not ready' error because the kubeadm upgrade workflow strictly requires the target node to first be marked as unschedulable via `kubectl cordon`, which prevents new pods from being scheduled. Without this step, the node remains schedulable, and the upgrade process cannot safely drain and evict running workloads, leading to the readiness check failure. On the CKA exam, this scenario tests your understanding of the node lifecycle during upgrades—a common trap is assuming the node must be ready when in fact it must be unschedulable. Remember the sequence: cordon first, then drain, then upgrade. A useful memory tip is "Cordon before you cordon off the upgrade"—the node must be locked down before kubeadm can touch it.
CKA Practice Question: Cluster Architecture, Installation and Configuration
This CKA practice question tests your understanding of cluster architecture, installation and configuration. 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.
During a cluster upgrade using kubeadm, after upgrading the control plane, you attempt to upgrade a worker node. The command `kubeadm upgrade node` fails with the error 'node is not ready'. 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 worker node has not been cordoned.
Option D is correct because `kubeadm upgrade node` requires the node to be in a schedulable state to perform the upgrade. If the node is not cordoned first, the upgrade process may fail with a 'node is not ready' error, as the kubeadm workflow expects the node to be drained and marked as unschedulable before proceeding. Cordon ensures the node is marked as unschedulable, preventing new pods from being scheduled during the upgrade.
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 worker node has a newer version of kubelet than the control plane.
Why it's wrong here
Version skew policy requires worker kubelet version <= control plane version, but this error is about node readiness.
✗
The worker node's kube-proxy is outdated.
Why it's wrong here
kube-proxy version does not affect kubeadm upgrade node readiness check.
✗
The kubelet on the worker node has not been restarted.
Why it's wrong here
Restarting kubelet is not required before upgrade; cordoning is needed.
✓
The worker node has not been cordoned.
Why this is correct
Before upgrading a worker node, it must be cordoned to prevent new Pods; the upgrade command requires the node to be in a maintainable state.
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 the 'node is not ready' error refers to the kubelet health status, but in the context of `kubeadm upgrade node`, it specifically indicates that the node has not been cordoned before the upgrade attempt.
Detailed technical explanation
How to think about this question
The `kubeadm upgrade node` command performs pre-flight checks, including verifying that the node is not already cordoned or drained, but it does not automatically cordon the node. In a real-world scenario, failing to cordon the node before running the upgrade can lead to race conditions where new pods are scheduled onto the node during the upgrade, causing the kubelet to reject them and the node to become NotReady. The correct workflow is to first run `kubectl cordon <node>` and `kubectl drain <node> --ignore-daemonsets`, then execute `kubeadm upgrade node`, and finally uncordon the node after the upgrade completes.
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 CKA 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 CKA question in full detail.
Cluster Architecture, Installation and Configuration — This question tests Cluster Architecture, Installation and Configuration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The worker node has not been cordoned. — Option D is correct because `kubeadm upgrade node` requires the node to be in a schedulable state to perform the upgrade. If the node is not cordoned first, the upgrade process may fail with a 'node is not ready' error, as the kubeadm workflow expects the node to be drained and marked as unschedulable before proceeding. Cordon ensures the node is marked as unschedulable, preventing new pods from being scheduled during the upgrade.
What should I do if I get this CKA 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This CKA 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 CKA exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.