CKA Workloads & Scheduling Practice Question
You are managing a Kubernetes cluster with three worker nodes. A deployment named 'frontend' is configured with 3 replicas. After a node failure, you notice that only 2 pods are running, and the third pod is stuck in 'Pending' state. The remaining nodes have sufficient CPU and memory. You check the deployment events and find no errors. You also verify that the PersistentVolumeClaims (PVCs) used by the deployment are bound. What is the most likely reason the third pod is not scheduled?
⚠ Common exam trap
A common mix-up: candidates assume resource constraints or scheduler failures are the default cause for pending pods, overlooking that a nodeSelector or affinity rule can silently prevent scheduling even when resources are abundant.
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 has a nodeSelector that only matches the failed node.
A nodeSelector that exclusively matches the failed node would prevent the scheduler from placing the pod on any other node, even if those nodes have sufficient resources. Since the failed node is unavailable, the pod remains in 'Pending' state indefinitely, as no other node satisfies the constraint.
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 ReplicaSet controller is not creating a new pod because the deployment's progressDeadlineSeconds has expired.
Why it's wrong here
The progressDeadlineSeconds parameter defines the duration the deployment controller waits for a deployment to progress before reporting a failed progress status. It does not halt the ReplicaSet controller from attempting to create or reconcile pods to meet the desired replica count.
- ✗
The PersistentVolumeClaims are using 'WaitForFirstConsumer' binding mode and the pod is pending because the volume is not yet bound.
Why it's wrong here
If the PersistentVolumeClaims are already in a Bound state, the WaitForFirstConsumer volume binding mode has already served its purpose during the initial scheduling phase. A pending pod in this scenario is not waiting for volume binding, as the storage resources have already been successfully provisioned and associated with the claims.
- ✗
The kube-scheduler is down or misconfigured.
Why it's wrong here
A completely failed or misconfigured kube-scheduler would prevent all new pods across the entire cluster from being scheduled, leaving them in a Pending state. Since other pods are actively running and scheduling normally on the remaining healthy worker nodes, the control plane's scheduling component is functioning correctly.
- ✓
The pod has a nodeSelector that only matches the failed node.
Why this is correct
When a pod specifies a nodeSelector that targets a unique label only present on the failed worker node, the kube-scheduler cannot find any other eligible nodes that satisfy this constraint. Consequently, the pod remains unschedulable and stuck in a Pending state, even though other healthy worker nodes are available in the cluster.
Go deeper
Related to this question
Learn chapter
Troubleshooting Cluster and Node Issues
Key term
Node Affinity
Node Affinity is a set of rules used by Kubernetes to determine which nodes a pod can be scheduled on, based on labels assigned to the nodes.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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