CKA Workloads and Scheduling Practice Question
A pod has tolerations for a taint with key 'dedicated', value 'gpu', and effect 'NoSchedule'. The pod's nodeSelector is {disktype: ssd}. Which node(s) can this pod be scheduled on? (Assume node1 has taint dedicated=gpu:NoSchedule and label disktype=ssd; node2 has taint dedicated=gpu:NoSchedule and label disktype=hdd; node3 has no taint and label disktype=ssd)
⚠ Common exam trap
Watch out — candidates often think tolerations are required to match taints on all nodes, forgetting that a node without the taint is also eligible, and they may overlook that nodeSelector is a separate, mandatory constraint that can exclude nodes even if they are tolerated.
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
✓
node1 and node3
The pod has a toleration for the taint dedicated=gpu:NoSchedule, so it can tolerate that taint on any node. However, the pod also has a nodeSelector requiring disktype=ssd. Node1 has both the tolerated taint and the required label, so it qualifies. Node3 has no taint and the required label, so it also qualifies. Node2 has the tolerated taint but its label is disktype=hdd, which does not match the nodeSelector, so it is excluded. Therefore, only node1 and node3 can schedule the pod.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
node1 only
Why it's wrong here
This answer omits node3, which is schedulable because it has no taint at all. Tolerations are required only for nodes carrying a matching taint; a pod can always land on an untainted node even if its toleration doesn't apply. Since node3 also satisfies the nodeSelector (disktype=hdd), node1-only undercounts the eligible nodes and is therefore incorrect.
- ✗
node2 and node3
Why it's wrong here
This option incorrectly includes node2. Node2 fails the pod's nodeSelector because it is missing the disktype=hdd label (or has a different value), and tolerations do not override label-based selection. Node3 is indeed eligible, but the presence of node2 makes this set wrong because the kube-scheduler filters out nodes whose labels do not match the selector before taint/toleration logic is considered.
- ✗
node1, node2, and node3
Why it's wrong here
Including node2 is the critical flaw here. Node2 does not carry the disktype=hdd label required by the nodeSelector, so it is filtered out during the scheduling predicates regardless of whether its taints are tolerated. NodeSelector is a hard constraint independent of taints/tolerations; consequently, the eligible set cannot be all three nodes, and this answer must be rejected.
- ✓
node1 and node3
Why this is correct
Node1 qualifies because it satisfies the nodeSelector and has a toleration that matches the dedicated taint, so the taint is effectively ignored. Node3 qualifies because it has no taint, meaning no toleration is needed, and it also satisfies the nodeSelector. Node2 is excluded because it fails the nodeSelector label requirement. Thus the correct schedulable set is node1 and node3.
Go deeper
Related to this question
Learn chapter
Troubleshooting Cluster and Node Issues
Key term
Node Affinity
Node Affinity is a set of rules used by Kubernetes to determine which nodes a pod can be scheduled on, based on labels assigned to the nodes.
Key term
Taints and Tolerations
Taints and tolerations are Kubernetes features that control which pods can be scheduled onto which nodes by marking nodes with a taint and allowing pods to declare a toleration to the taint.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CKA 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 CKA exam.