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2.05 Node Affinity

n-affinity

n-affinity1

  • Node Affinity provides advanced control over pod placement compared to NodeSelector.
  • Defined under spec > affinity > nodeAffinity.
  • Uses matchExpressions with key, operator, and values.
  • Example: In, NotIn, Exists.
  • Example rules:
  • Place pod on Large or Medium nodes.
  • Avoid scheduling on Small nodes.
  • Match nodes where label size exists.

Node Affinity Types

n-affinity-types

  • Two stages in pod lifecycle:
  • DuringScheduling – pod creation.

  • DuringExecution – pod already running.

  • Available Types:

  • requiredDuringSchedulingIgnoredDuringExecution → Pod scheduled only if matching node exists.

  • preferredDuringSchedulingIgnoredDuringExecution → Tries matching node, falls back to any node.

  • Planned Type:

  • requiredDuringSchedulingRequiredDuringExecution → Will enforce rules even after pod is running.

Behavior Summary

  • Required: Pod won’t be scheduled without a matching node.
  • Preferred: Scheduler tries to match, but runs pod elsewhere if needed.
  • Ignored During Execution: Running pods are not affected if labels change later.

n-affinity-types2