CKS Cluster Setup Practice Question
A team needs to set up a highly available Kubernetes control plane across three availability zones. What is the minimum number of etcd members required to achieve fault tolerance against one zone failure?
⚠ Common exam trap
CNCF often tests the misconception that you need an even number of etcd members for high availability, but the Raft consensus algorithm requires an odd number to avoid split-brain scenarios, and the minimum for fault tolerance against one failure is three, not five or seven.
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
✓
3
For a highly available Kubernetes control plane across three availability zones, the etcd cluster must tolerate the loss of one entire zone. With three etcd members, one per zone, the cluster requires a majority (2) to form quorum. If one zone fails, the remaining two members still constitute a majority, ensuring continued operation. This matches the minimum odd number greater than one that provides fault tolerance against a single failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
5
Why it's wrong here
A 5-member control plane can tolerate two simultaneous failures while maintaining etcd quorum, but the question asks for the minimum required for high availability. Three nodes are sufficient to form a majority and provide HA; five adds unnecessary cost and operational overhead. Choosing 5 violates the 'minimum' constraint even though it is a valid HA configuration.
- ✗
1
Why it's wrong here
A single control plane node cannot tolerate any failure because there is no redundant member to maintain etcd quorum; an etcd cluster with one member loses quorum entirely if that member goes down. High availability requires at least three nodes, so one is fundamentally inadequate. This option represents a single point of failure, not a highly available setup.
- ✓
3
Why this is correct
Three control plane nodes are the minimum required for high availability because etcd quorum for a 3-node cluster is two, meaning the cluster can survive the loss of one node. With only two nodes, a single failure would leave one node and no majority, so three is the smallest odd number that provides fault tolerance. This is the standard recommendation for production Kubernetes control planes.
- ✗
7
Why it's wrong here
A 7-member control plane can withstand up to three failures, but it is far above the minimum and creates performance drawbacks; each write must be replicated to a majority of seven nodes, increasing latency and network overhead. The question specifically asks for the minimum, and three already provides the required HA with one-failure tolerance. Extending to seven is not incorrect for HA, but it violates the 'minimum' criterion and can degrade etcd performance.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CKS 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 CKS exam.