This CKA practice question tests your understanding of troubleshooting. 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 run kubectl get nodes and see one node is NotReady. The kubelet is running on the node. 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.
The kubelet is not installed
Why wrong: Question states kubelet is running.
The node has been cordoned
Why wrong: Cordoning makes node Unschedulable, not NotReady.
The API server is down
Why wrong: If API server is down, kubectl get nodes would fail, not show NotReady.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Network connectivity issue between kubelet and API server
When a node is NotReady but the kubelet is running, the most common cause is a network connectivity issue between the kubelet and the API server. The kubelet reports node status via periodic heartbeats (node-status-update-frequency, default 10s) and if the API server cannot receive these updates due to network problems (e.g., firewall rules, DNS resolution failure, or dropped packets), the node controller marks the node as NotReady after the node-monitor-grace-period (default 40s). The kubelet being running eliminates installation issues, and the API server being down would affect all nodes, not just one.
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.
The kubelet is not installed
Why it's wrong here
Question states kubelet is running.
The node has been cordoned
Why it's wrong here
Cordoning makes node Unschedulable, not NotReady.
The API server is down
Why it's wrong here
If API server is down, kubectl get nodes would fail, not show NotReady.
Option-by-option analysis
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The CKA exam frequently reuses these exact scenarios with slightly different constraints.
Why this is wrong here
Question states kubelet is running.
Why this is wrong here
Cordoning makes node Unschedulable, not NotReady.
Why this is wrong here
If API server is down, kubectl get nodes would fail, not show NotReady.
Analysis generated from the official CKAblueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
The trap here is that candidates confuse 'cordon' (which affects scheduling but not readiness) with 'NotReady' (which indicates a health or connectivity failure), leading them to pick Option C when the node is actually unreachable.
Trap categories for this question
Command / output trap
If API server is down, kubectl get nodes would fail, not show NotReady.
Detailed technical explanation
The kubelet creates a Lease object in the kube-node-lease namespace to report heartbeats, reducing API server load compared to updating the Node object directly. The node controller checks the Lease's renewTime; if it exceeds the node-monitor-grace-period (default 40s), the node is marked NotReady, and after the pod-eviction-timeout (default 5m), pods are evicted. In a real-world scenario, a misconfigured network policy or a flapping network interface can cause intermittent heartbeats, leading to a NotReady state even though the kubelet process is healthy.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
The correct answer is: Network connectivity issue between kubelet and API server — When a node is NotReady but the kubelet is running, the most common cause is a network connectivity issue between the kubelet and the API server. The kubelet reports node status via periodic heartbeats (node-status-update-frequency, default 10s) and if the API server cannot receive these updates due to network problems (e.g., firewall rules, DNS resolution failure, or dropped packets), the node controller marks the node as NotReady after the node-monitor-grace-period (default 40s). The kubelet being running eliminates installation issues, and the API server being down would affect all nodes, not just one.
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 11, 2026
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.
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