Understanding Kubernetes: Part 23 Node Selector

📢 If you’ve been following our Kubernetes series 2025, welcome back! For new readers, check out Part 22: Resource Requests & Limits

What is Node Selector in Kubernetes?

In Kubernetes, a Node Selector is a simple way to constrain a pod to run on a specific set of nodes. It ensures that your workloads are scheduled on the appropriate nodes based on labels assigned to them.

• Labels: Key-value pairs assigned to nodes that categorize them based on attributes like hardware type, region, or purpose.

• nodeSelector: A field in the pod specification that matches node labels to schedule pods on specific nodes.

Why Use Node Selector?

✅ Hardware Optimization: Schedule workloads on nodes with specific CPU, memory, or GPU capabilities. ✅ Cost Efficiency: Run cost-sensitive workloads on cheaper node pools. ✅ High Availability: Ensure critical workloads run on dedicated nodes for reliability. ✅ Compliance & Security: Deploy sensitive applications on isolated nodes for security.

Example YAML for Node Selector

apiVersion: v1
kind: Pod
metadata:
  name: node-selector-demo
spec:
  nodeSelector:
    disktype: ssd
  containers:
    - name: my-app
      image: my-app:latest

Explanation:

• nodeSelector: Ensures that the pod runs only on nodes labeled with disktype=ssd.

• Node Labels: Nodes must have the appropriate label, which can be set using:

• kubectl label nodes <node-name> disktype=ssd

This method provides a basic way to control pod placement but lacks flexibility for complex scheduling needs.

In My Previous Role

As a Senior DevOps Engineer, I used Node Selectors to optimize workload placement:

• Ensuring High Performance: Scheduled machine learning workloads on GPU-enabled nodes.

• Cost Savings: Deployed batch jobs on spot instances using labeled node pools.

• Cluster Stability: Segregated frontend and backend services onto different node groups.

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