Quick Answer
The answer is that the pod is stuck in a Pending state because it does not tolerate the node-role.kubernetes.io/master taint present on the control plane node. This occurs because the Kubernetes scheduler evaluates node taints against pod tolerations; when a node has a taint that a pod lacks a matching toleration for, the scheduler excludes that node from placement. In this scenario, the master node’s default taint repels all pods without an explicit toleration, leaving zero available nodes and causing the pod to remain Pending. On the CKA exam, this tests your understanding of taints and tolerations as core scheduling constraints, often appearing in troubleshooting scenarios where a pod refuses to land on a specific node. A common trap is assuming the master node is always available for workloads, but by design it is tainted to reserve it for system components. Memory tip: “Taint without toleration equals no destination.”
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.
A pod is stuck in 'Pending' state. 'kubectl describe pod' shows '0/1 nodes are available: 1 node(s) had taint {node-role.kubernetes.io/master: }, that the pod didn't tolerate'. 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 pod is missing resource requests.
Why wrong: Resource requests would cause insufficient CPU/memory, not taint tolerance.
The pod does not tolerate the node's taint.
The taint is preventing scheduling unless the pod has a toleration.
The node is cordoned.
Why wrong: Cordoning shows 'SchedulingDisabled', not taint messages.
The kubelet is not running on the node.
Why wrong: If kubelet is not running, the node would be '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
The pod does not tolerate the node's taint.
The pod is stuck in 'Pending' because the scheduler cannot find a node that satisfies its scheduling constraints. The 'kubectl describe pod' output explicitly states that 1 node has a taint (node-role.kubernetes.io/master) that the pod does not tolerate. By default, pods do not tolerate the master taint, so they are not scheduled onto master nodes unless a toleration is added. This is the direct cause of the pending state.
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 pod is missing resource requests.
Why it's wrong here
Resource requests would cause insufficient CPU/memory, not taint tolerance.
The pod does not tolerate the node's taint.
Why this is correct
The taint is preventing scheduling unless the pod has a toleration.
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 node is cordoned.
Why it's wrong here
Cordoning shows 'SchedulingDisabled', not taint messages.
The kubelet is not running on the node.
Why it's wrong here
If kubelet is not running, the node would be 'NotReady'.
Common exam traps
The trap here is that candidates may confuse taints with node cordoning or resource constraints, but the specific error message about 'taint that the pod didn't tolerate' directly points to a toleration mismatch, not a resource or node readiness issue.
Trap categories for this question
Command / output trap
Cordoning shows 'SchedulingDisabled', not taint messages.
Detailed technical explanation
Taints and tolerations work as a mechanism to repel or allow pods onto nodes. The master node typically has a taint 'node-role.kubernetes.io/master:NoSchedule' to prevent user workloads from running on it. Pods can override this by specifying a toleration in their spec. In real-world scenarios, this is often seen when a cluster has only one node (a single-node control plane) and users forget to remove the master taint or add tolerations to their pods.
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 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.
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
Cluster Architecture, Installation and Configuration — This question tests Cluster Architecture, Installation and Configuration — Read the scenario before looking for a memorised answer..
The correct answer is: The pod does not tolerate the node's taint. — The pod is stuck in 'Pending' because the scheduler cannot find a node that satisfies its scheduling constraints. The 'kubectl describe pod' output explicitly states that 1 node has a taint (node-role.kubernetes.io/master) that the pod does not tolerate. By default, pods do not tolerate the master taint, so they are not scheduled onto master nodes unless a toleration is added. This is the direct cause of the pending state.
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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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A pod is stuck in 'Pending' state. 'kubectl describe pod' shows '0/1 nodes are available: 1 node(s) had taint {node.kubernetes.io/unreachable: }, that the pod didn't tolerate'. What does this indicate?
hardWhy C: The error message indicates that the node has a taint of `node.kubernetes.io/unreachable`, which is automatically added by the node controller when the control plane cannot communicate with the node (e.g., due to network failure or kubelet being down). The pod remains in 'Pending' because no node is available that tolerates this taint, meaning the node is unreachable from the control plane. This matches option C.
Last reviewed: Jun 24, 2026
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