CKA Workloads and Scheduling Practice Question
A DaemonSet named 'fluentd' is configured to run on all nodes. After adding a new node to the cluster, you notice that the DaemonSet pod is not running on the new node. What could be the cause?
⚠ Common exam trap
It's easy for candidates to confuse taints/tolerations with nodeSelector or resource constraints, assuming a new node would automatically accept all DaemonSet pods, when in fact taints are a common reason for scheduling failures on new nodes.
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
✓
The new node has a taint that the DaemonSet pod does not tolerate
A DaemonSet ensures that a copy of a pod runs on all (or a subset of) nodes. When a new node is added, the DaemonSet controller automatically schedules a pod on it unless the node has a taint that the pod does not tolerate. By default, the new node may have a taint (e.g., `node.kubernetes.io/unschedulable` or a custom taint) that prevents the DaemonSet pod from being scheduled unless the pod's spec includes a matching toleration.
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 new node has a taint that the DaemonSet pod does not tolerate
Why this is correct
A DaemonSet controller is designed to ensure a pod runs on every eligible node. If a new node joins the cluster and has a taint, but the DaemonSet's pod template does not include a corresponding toleration, the Kubernetes scheduler will prevent the DaemonSet pod from being placed on that specific node. This is a common scenario for specialized nodes, such as master nodes, which often have `node-role.kubernetes.io/master:NoSchedule` taints by default, requiring explicit tolerations for DaemonSets like `kube-proxy` or `fluentd` to run on them.
- ✗
The new node does not have enough resources to run the DaemonSet pod
Why it's wrong here
If a new node lacks sufficient CPU or memory resources to accommodate the DaemonSet pod's requests, the DaemonSet controller would still successfully create the pod object in the API server. However, the Kubernetes scheduler would then mark this pod as `Pending` and continuously attempt to schedule it, rather than the pod simply not appearing. The absence of the pod object itself indicates a different underlying issue than resource scarcity, as the controller's job is to create the pod, not to schedule it.
- ✗
The DaemonSet has a nodeSelector that does not match the new node's labels
Why it's wrong here
If a nodeSelector is configured, it would prevent scheduling on any node that doesn't match, not just new nodes. The question says 'configured to run on all nodes', implying no nodeSelector or it matches all.
- ✗
The DaemonSet's update strategy is set to OnDelete
Why it's wrong here
The `OnDelete` update strategy for a DaemonSet dictates how existing DaemonSet pods are handled when the DaemonSet's pod template is modified or when a pod is manually deleted. It specifically means that pods are only recreated or updated if they are explicitly deleted, or if the DaemonSet template changes. However, this strategy has no bearing on the DaemonSet controller's fundamental responsibility to automatically create new pods on any *new* nodes that join the cluster, regardless of the update strategy configured.
Go deeper
Related to this question
Learn chapter
Kubernetes Architecture Overview
Key term
Network Policies
A Kubernetes resource that controls how pods communicate with each other and with other network endpoints, acting as a firewall for pod-to-pod traffic.
Key term
DaemonSets
A DaemonSet is a Kubernetes object that ensures a copy of a specific pod runs on every node in a cluster, or on a subset of nodes.
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