Day 19beginnerFeb 19, 2026

Master Kubernetes Labels and Selectors

Labels and selectors are how Kubernetes connects everything — get them wrong and nothing talks to anything.

kuberneteslabelsfundamentals

What

Labels are key-value pairs attached to Kubernetes objects like Pods, Services, and Deployments. Selectors filter objects by their labels. Together they form the backbone of how Kubernetes connects Services to Pods, Deployments to ReplicaSets, and NetworkPolicies to targets.

Why It Matters

Almost every Kubernetes resource relies on label matching to function. Services use selectors to find their backend pods. Deployments use matchLabels to manage ReplicaSets. If your labels don't align, traffic won't route, scaling won't work, and deployments will silently fail.

Example

# Add labels in your Pod or Deployment YAML
metadata:
  labels:
    app: web
    env: prod
    version: v2

# Service selector must match pod labels
spec:
  selector:
    app: web
    env: prod

# Query pods by label from CLI
kubectl get pods -l app=web,env=prod

# Show labels on all pods
kubectl get pods --show-labels

# Add a label to an existing pod
kubectl label pod my-pod tier=frontend

yaml

Common Mistake

Mismatching labels between a Service selector and Pod template, causing the Service to route to zero pods. The Service shows endpoints: <none> and all requests fail.

Quick Fix

Run `kubectl describe service <name>` and check the Endpoints field. If it says <none>, compare the Service selector to your Pod labels with `kubectl get pods --show-labels`. Fix the mismatch.