Node Selectors

Node Selectors (Scheduling)

In Kubernetes, nodeSelector is the simplest way to constrain a Pod to only run on nodes with specific labels.

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📄 Example Pod Definition

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
spec:
  containers:
    - name: data-processor
      image: data-processor
  nodeSelector:
    size: Large

This pod will only be scheduled on a node with the label size=Large.

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🏷️ Labeling Nodes

You can label a node using:

kubectl label nodes <node-name> <label-key>=<label-value>

Example:

kubectl label nodes node-1 size=Large

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⚠️ Limitations

• nodeSelector uses exact match only (AND logic).
• You cannot use OR logic (e.g., Large OR Medium).
• You cannot use inequalities or expressions (e.g., !=Small).
• For advanced scheduling, see: Node Affinity

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🧠 When to Use

• For simple node filtering based on static labels.
• If node groups are well-defined (e.g., GPU=true, size=Large).
• For quick testing or enforcing strict placement.

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✅ Summary

Feature	Supported by nodeSelector
Match labels	✅ Yes
Match expressions	❌ No
OR logic	❌ No
Chained rules	❌ No

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👉 For more flexible scheduling rules (expressions, preferred rules), check out: Node Affinity →