KCNA Kubernetes Fundamentals Practice Question
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?
⚠ Common exam trap
CNCF often tests the distinction between Pod lifecycle phases (Pending vs. CrashLoopBackOff vs. ImagePullBackOff) to see if candidates confuse scheduling failures with runtime or image errors.
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
✓
There are insufficient resources on the nodes
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.
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 Service selector does not match
Why it's wrong here
A mismatched Service selector affects only traffic routing to already-running pods; it never prevents scheduling, so the third pod would still run. Selector mismatches are the cause when endpoints are empty despite healthy, Running pods.
- ✗
The Deployment name is misspelled
Why it's wrong here
A misspelled Deployment name would prevent the object from being created or found at all, not leave two pods running and one Pending. Name errors matter when kubectl reports NotFound or applies a separate, unintended Deployment.
- ✓
There are insufficient resources on the nodes
Why this is correct
The scheduler leaves a pod Pending when no node has enough allocatable CPU or memory to satisfy its requests. Insufficient cluster resources prevent the third replica from being placed, while the other two run normally.
- ✗
The container image is invalid
Why it's wrong here
An invalid image causes ImagePullBackOff or ErrImagePull, leaving the pod scheduled but not running; Pending means the scheduler cannot place it on any node. Invalid images are the cause when pods report image pull errors after successful scheduling.
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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.