K8s Troubleshooting — Target Pod Selector Misconfig

K8s Troubleshooting handbook

Note, full K8s troubleshooting mind map is available at: “K8s Troubleshooting MindMap”

In K8s, a Service routes traffic to Pods based on a label selector. If there’s a misconfiguration with the selector, the Service will not be able to route traffic correctly.

For example, consider the following Service:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376

This Service is configured to route traffic to Pods with the label app: my-app.

Now, let’s say you have a Deployment that creates Pods like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app-wrong  # Misconfigured label
    spec:
      containers:
      - name: my-app
        image: my-app:1.0
        ports:
        - containerPort: 9376

In the above Deployment, the Pods are created with the label app: my-app-wrong instead of app: my-app. Because the labels of the Pods don't match the selector of the Service, the Service won't…