CKA Workloads & Scheduling Practice Question
A Pod is in Pending state for a long time. 'kubectl describe pod' shows the event: '0/3 nodes are available: 3 node(s) had taints that the pod didn't tolerate'. What is the most likely issue?
⚠ Common exam trap
CNCF often tests the distinction between taints/tolerations and resource constraints, so candidates may incorrectly assume the error is about resource exhaustion when the event message explicitly mentions taints.
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 Pod does not have tolerations for the taints on the nodes.
The event '0/3 nodes are available: 3 node(s) had taints that the pod didn't tolerate' directly indicates that all nodes in the cluster have taints applied, and the Pod's spec does not include corresponding tolerations. Taints and tolerations work together to ensure that Pods are only scheduled onto nodes whose taints they tolerate; without matching tolerations, the scheduler will skip those nodes entirely, leaving the Pod in a Pending state.
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 nodes do not have enough CPU or memory to run the Pod.
Why it's wrong here
If the scheduling failure were caused by resource constraints, the kubectl describe pod output would explicitly show events with messages like FailedScheduling due to 'Insufficient cpu' or 'Insufficient memory'. However, the specific event output indicates that the pod is unschedulable due to node taints rather than resource exhaustion. Therefore, resource limits are not the root cause of this pending state.
- ✓
The Pod does not have tolerations for the taints on the nodes.
Why this is correct
When a node is tainted with a NoSchedule or NoExecute effect, the kube-scheduler will reject any pod that lacks matching tolerations. The kubectl describe pod output confirms this scenario by displaying a scheduling event indicating that the pod had 0/N nodes available due to untolerated taints. Adding the appropriate tolerations to the pod specification is required to allow scheduling on these nodes.
- ✗
The nodes are not tainted, but the Pod has tolerations.
Why it's wrong here
Pods with tolerations can freely schedule onto untainted nodes as long as other scheduling criteria like resource requests and node selectors are met. Tolerations do not act as a requirement for taints to be present; they merely allow a pod to bypass existing taints. If the nodes were untainted, the pod would have scheduled successfully instead of remaining in a pending state with taint-related warnings.
- ✗
The scheduler is not running.
Why it's wrong here
If the kube-scheduler control plane component were completely offline, no scheduling decisions or evaluations would occur at all. Consequently, the pod would remain in a Pending state indefinitely without generating any FailedScheduling events in its event log. The presence of detailed scheduling failure events in the kubectl describe output proves that the scheduler is active and actively rejecting the pod based on taint constraints.
Go deeper
Related to this question
Learn chapter
Troubleshooting Cluster and Node Issues
Key term
Taints and Tolerations
Taints and tolerations are Kubernetes features that control which pods can be scheduled onto which nodes by marking nodes with a taint and allowing pods to declare a toleration to the taint.
Key term
kubectl Command Reference
kubectl is the command-line tool used to interact with and manage Kubernetes clusters by sending commands to the Kubernetes API.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.