CKA Troubleshooting Practice Question
A pod is stuck in 'Pending' state. You run 'kubectl describe pod my-pod' and see the event: '0/4 nodes are available: 4 node(s) had taint {node.kubernetes.io/unreachable: }, that the pod didn't tolerate'. What is the likely cause?
⚠ Common exam trap
The CKA exam tests the distinction between taint-based scheduling failures and resource-based failures; the trap here is that candidates may confuse the 'unreachable' taint with resource constraints or PVC issues, but the event message explicitly names the taint key, which directly points to node reachability problems.
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 nodes are unreachable or have network issues
The event '0/4 nodes are available: 4 node(s) had taint {node.kubernetes.io/unreachable: }' indicates that all nodes in the cluster have the 'node.kubernetes.io/unreachable' taint, which is automatically applied by the node controller when a node becomes unreachable (e.g., due to network partition, node failure, or kubelet not reporting). Since the pod does not have a toleration for this taint, it cannot be scheduled on any node, resulting in a 'Pending' state. This is a classic scheduling failure caused by node unreachability, not by resource constraints or image issues.
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 pod's container image is not found
Why it's wrong here
If a pod's container image cannot be found or pulled, the pod will successfully pass the scheduling phase and bind to a node. Once scheduled, the kubelet on the destination node attempts to pull the image, resulting in an ImagePullBackOff or ErrImagePull status, rather than keeping the pod in a Pending state during the scheduling phase.
- ✗
The pod has a resource request that cannot be met by any node
Why it's wrong here
While insufficient CPU or memory requests can indeed keep a pod in a Pending state, the scheduler would emit a FailedScheduling event indicating 'Insufficient cpu' or 'Insufficient memory'. In this specific scenario, the describe output reveals taint-related scheduling failures, meaning the scheduler is blocking placement due to node taints rather than resource capacity limits.
- ✓
The nodes are unreachable or have network issues
Why this is correct
When a node becomes unreachable or experiences network partition issues, the node controller automatically applies the node.kubernetes.io/unreachable taint to it. Because the pending pod does not possess a matching toleration for this specific taint, the Kubernetes scheduler cannot assign the pod to any of these affected nodes, leaving it stuck in the Pending state.
- ✗
The PersistentVolumeClaim is not bound
Why it's wrong here
If an unbound PersistentVolumeClaim (PVC) were blocking the pod, the scheduler would emit a specific event such as FailedScheduling with a message like 'waiting for first consumer to be created' or 'volume node affinity conflict'. This differs from the taint-related events shown in the describe output, which point directly to node unreachability issues rather than storage provisioning delays.
Go deeper
Related to this question
Learn chapter
Troubleshooting Cluster and Node Issues
Key term
Ingress Resources
Ingress Resources are Kubernetes API objects that manage external access to services inside a cluster, typically HTTP and HTTPS traffic, by defining rules for routing requests based on hostnames and paths.
Key term
Network Policies
A Kubernetes resource that controls how pods communicate with each other and with other network endpoints, acting as a firewall for pod-to-pod traffic.
About these practice questions
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JA
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.