coredns: Tighten PDB to maxUnavailable 33% and always allow unhealthy pod eviction - #18679
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kubernetes-prow[bot] merged 2 commits intoAug 10, 2026
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… pod eviction The PodDisruptionBudget exists to guarantee DNS serving capacity, and a single CoreDNS instance handles far more QPS than clusters of this size generate, so the meaningful floor is redundancy: voluntary disruptions should never reduce the deployment below two pods. With 50%, a cluster running three replicas allows two simultaneous evictions, leaving a single DNS pod. 33% is the largest percentage that keeps at least two pods whenever the dns-autoscaler runs three or more replicas, while still scaling the number of allowed disruptions with the deployment. This also matches the availability posture EKS converged on for its managed CoreDNS add-on. unhealthyPodEvictionPolicy: AlwaysAllow lets a running-but-not-ready CoreDNS pod be evicted even when the budget is exhausted, so a wedged pod no longer blocks the drain of its own node. A pod that is not ready serves no traffic, so evicting it never reduces capacity. The field is GA and locked on since Kubernetes 1.31, below the oldest version kOps supports.
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The PodDisruptionBudget exists to guarantee DNS serving capacity, and a single CoreDNS instance handles far more QPS than clusters of this size generate, so the meaningful floor is redundancy: voluntary disruptions should never reduce the deployment below two pods. With 50%, a cluster running three replicas allows two simultaneous evictions, leaving a single DNS pod. 33% is the largest percentage that keeps at least two pods whenever the dns-autoscaler runs three or more replicas, while still scaling the number of allowed disruptions with the deployment. This also matches the availability posture EKS converged on for its managed CoreDNS add-on.
unhealthyPodEvictionPolicy: AlwaysAllowlets a running-but-not-ready CoreDNS pod be evicted even when the budget is exhausted, so a wedged pod no longer blocks the drain of its own node. A pod that is not ready serves no traffic, so evicting it never reduces capacity./cc @rifelpet @ameukam
Refs: #18677