Scheduling: Taints Quiz

The single most common Kubernetes misunderstanding: a toleration does not attract a pod to a node. It only permits one. Taints repel, tolerations allow, and node affinity is the mechanism that actually attracts. Get that straight and most of this topic falls into place.

What this quiz covers

• Taint effects — NoSchedule, PreferNoSchedule, NoExecute, and what happens to pods already running
• Toleration operators — Equal against Exists, and what a bare Exists tolerates
• tolerationSeconds — how long a pod survives a NoExecute taint appearing
• Node affinity — requiredDuringSchedulingIgnoredDuringExecution against preferredDuringSchedulingIgnoredDuringExecution
• Using both together — dedicated nodes need a taint and an affinity rule
• Over-tainting — what happens to schedulability when the rules pile up

Common mistakes

• Expecting a toleration to place a pod on a specific node — it won’t; that’s affinity’s job
• Forgetting NoExecute evicts pods that are already running
• Assuming IgnoredDuringExecution means the rule is re-evaluated later; it isn’t

Twenty questions below, each with an explanation.

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