KCNA Kubernetes Fundamentals Practice Question
A developer created a Deployment with 5 replicas. After applying the manifest, only 3 pods are Running; the other 2 are Pending. Which is the MOST likely cause?
⚠ Common exam trap
The exam often tests the distinction between Pod lifecycle phases (Pending, Running, Failed) and readiness/liveness probes; the trap here is confusing a scheduling failure (Pending) with a runtime failure (CrashLoopBackOff) or network restriction (NetworkPolicy).
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 do not have enough available CPU or memory to schedule the additional pods
D is correct because when a Pod remains in Pending state, it indicates that the scheduler cannot find a node that satisfies the Pod's resource requests. Since 3 Pods are already running and consuming resources, the remaining 2 Pods cannot be placed if the cluster's nodes lack sufficient allocatable CPU or memory. This is a classic resource-constrained scheduling failure, not a runtime or network issue.
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 readiness probe is failing
Why it's wrong here
A failing readiness probe leaves the pod in Running but NotReady, and it is removed from Service endpoints; it does not affect scheduling. Pending means no node was assigned, typically due to insufficient allocatable CPU or memory. A readiness probe would be the answer when pods run yet receive no traffic.
- ✗
A NetworkPolicy is blocking traffic to the pods
Why it's wrong here
NetworkPolicy filters packet flow to running pods; it cannot prevent scheduling, so pods would be Running but unreachable. Pending indicates the scheduler found no node satisfying resource requests or constraints. A NetworkPolicy would be the answer when pods run but connections to them time out or are refused.
- ✗
The container image is misspelled
Why it's wrong here
A misspelled image name causes ImagePullBackOff or ErrImagePull, leaving pods stuck in that waiting state, not Pending. Pending means the scheduler cannot place the pod, usually from insufficient CPU or memory requests on nodes. A bad image name would be the answer when pods show ImagePullBackOff events.
- ✓
The nodes do not have enough available CPU or memory to schedule the additional pods
Why this is correct
Pending means the scheduler cannot bind the pods to any node. Insufficient allocatable CPU or memory leaves no node satisfying the pod's resource requests, so the remaining two replicas stay unscheduled while three already-placed pods run.
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Same concept, more angles
2 more ways this is tested on KCNA
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. An administrator runs 'kubectl get pods' and sees that a pod is in 'Pending' state. 'kubectl describe pod' shows the event: '0/4 nodes are available: 1 node had taints that the pod didn't tolerate, 3 nodes had insufficient memory'. What is the most likely issue?
medium- A.The node with the taint has a toleration mismatch.
- B.The pod's image pull is failing.
- ✓ C.The pod's resource requests exceed available memory on three nodes.
- D.The pod was evicted due to resource pressure.
Why C: The scheduler event explicitly states '3 nodes had insufficient memory', which directly indicates that the pod's resource requests (specifically memory) exceed the available allocatable memory on those three nodes. The fourth node is unavailable due to taints, leaving zero schedulable nodes, hence the 'Pending' state.
Variation 2. A Deployment is created with `replicas: 3`. After applying the manifest, only 2 pods are running and one is in Pending state. What is the most likely reason?
medium- A.The Service selector does not match
- B.The Deployment name is misspelled
- ✓ C.There are insufficient resources on the nodes
- D.The container image is invalid
Why C: When a Pod remains in Pending state, it means the scheduler cannot find a node that satisfies the Pod's resource requirements (CPU, memory, or other constraints). Since two Pods are running successfully, the Deployment configuration (image, name, selector) is valid, and the issue is that the cluster lacks sufficient capacity to schedule the third replica. The scheduler continuously evaluates node resources and will leave the Pod pending until resources become available or the request is adjusted.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This KCNA 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 KCNA exam.