- A
NetworkPolicy
Why wrong: NetworkPolicy controls traffic, not injection.
- B
Service
Why wrong: Services expose pods, but do not inject sidecars.
- C
MutatingAdmissionWebhook
Service meshes like Istio use a mutating webhook to automatically inject the Envoy sidecar proxy.
- D
ConfigMap
Why wrong: ConfigMaps store configuration data, not inject sidecars.
Question 742 of 997
Mutating Admission Webhook — Injecting Sidecar Proxies for Service Mesh
This KCNA practice question tests your understanding of cloud native architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which Kubernetes resource is commonly used to implement the sidecar pattern for injecting a service mesh proxy?
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
✓
MutatingAdmissionWebhook
Option C is correct because a MutatingAdmissionWebhook intercepts Pod creation requests and automatically injects a sidecar container (e.g., Envoy or Linkerd-proxy) into the Pod spec. This is the standard mechanism used by service mesh control planes like Istio and Linkerd to transparently add the proxy without modifying application manifests.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
NetworkPolicy
Why it's wrong here
NetworkPolicy controls traffic, not injection.
- ✗
Service
Why it's wrong here
Services expose pods, but do not inject sidecars.
- ✓
MutatingAdmissionWebhook
Why this is correct
Service meshes like Istio use a mutating webhook to automatically inject the Envoy sidecar proxy.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
ConfigMap
Why it's wrong here
ConfigMaps store configuration data, not inject sidecars.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the misconception that a Service or NetworkPolicy is responsible for sidecar injection, when in fact only a mutating admission webhook can automatically modify Pod specs at creation time.
Detailed technical explanation
How to think about this question
Under the hood, the MutatingAdmissionWebhook is called by the kube-apiserver before the Pod is persisted; it receives an AdmissionReview JSON object and returns a JSON Patch (RFC 6902) that adds the sidecar container, volumes, and environment variables. In Istio, the webhook is configured via a ValidatingWebhookConfiguration and MutatingWebhookConfiguration, and the sidecar proxy uses iptables rules to intercept all inbound and outbound traffic via a redirect to the proxy’s port (e.g., 15001 for Envoy).
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Cloud Native Architecture — study guide chapter
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FAQ
Questions learners often ask
What does this KCNA question test?
Cloud Native Architecture — This question tests Cloud Native Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: MutatingAdmissionWebhook — Option C is correct because a MutatingAdmissionWebhook intercepts Pod creation requests and automatically injects a sidecar container (e.g., Envoy or Linkerd-proxy) into the Pod spec. This is the standard mechanism used by service mesh control planes like Istio and Linkerd to transparently add the proxy without modifying application manifests.
What should I do if I get this KCNA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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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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