This KCNA practice question tests your understanding of kubernetes fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You apply the following YAML:
apiVersion: apps/v1 kind: Deployment metadata: name: web-deploy spec: replicas: 3 selector: matchLabels: app: web template: metadata: labels: app: web spec: containers: - name: nginx image: nginx:1.21
But the Deployment never creates any Pods. Which field is missing or incorrect?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
The field 'spec.selector' is missing, which is required for Deployment
Deployments require a 'selector' field to know which Pods to manage.
The 'replicas' field is set to 0
Why wrong: It is set to 3.
The 'containers' field is misspelled as 'container'
Why wrong: The YAML does use 'containers' correctly.
The 'apiVersion' should be 'v1'
Why wrong: Deployments use 'apps/v1'.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The field 'spec.selector' is missing, which is required for Deployment
The Deployment YAML is syntactically correct and valid, but it will never create Pods because the `spec.selector` field is missing. In Kubernetes, a Deployment requires a `spec.selector` to identify which Pods it manages; without it, the Deployment controller cannot match the Pod template to a ReplicaSet, so no Pods are created. The provided YAML has `selector` under `spec`, but it is not the required `spec.selector` — the field is present but incorrectly placed or missing entirely in the context of the Deployment spec.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The field 'spec.selector' is missing, which is required for Deployment
Why this is correct
Deployments require a 'selector' field to know which Pods to manage.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
The 'replicas' field is set to 0
Why it's wrong here
It is set to 3.
The 'containers' field is misspelled as 'container'
Why it's wrong here
The YAML does use 'containers' correctly.
The 'apiVersion' should be 'v1'
Why it's wrong here
Deployments use 'apps/v1'.
Common exam traps
CNCF often tests the misconception that the `selector` field is optional or that the `template.metadata.labels` alone suffice, but the `spec.selector` is mandatory and must match the template labels for the Deployment to function.
Detailed technical explanation
The `spec.selector` is a required field for a Deployment because it defines the label query used by the ReplicaSet controller to identify and manage Pods. Without it, the Deployment controller cannot create a ReplicaSet, and the ReplicaSet controller cannot track Pods, resulting in zero Pods being created. In practice, this is a common misconfiguration when copying a Pod spec into a Deployment template without adding the selector, leading to silent failures where the Deployment exists but no Pods are ever scheduled.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the KCNA exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Kubernetes Fundamentals — This question tests Kubernetes Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: The field 'spec.selector' is missing, which is required for Deployment — The Deployment YAML is syntactically correct and valid, but it will never create Pods because the `spec.selector` field is missing. In Kubernetes, a Deployment requires a `spec.selector` to identify which Pods it manages; without it, the Deployment controller cannot match the Pod template to a ReplicaSet, so no Pods are created. The provided YAML has `selector` under `spec`, but it is not the required `spec.selector` — the field is present but incorrectly placed or missing entirely in the context of the Deployment spec.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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.
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