LAB11b: Label Selector

LAB60: Labeling Resources correctly

Demonstrate why labels matter — especially when two Services accidentally point to the same Pods because they share the same labels.

Two apps:

• hello.xyz → “Hello! Nice to meet you!”

• bye.xyz → “Bye! See you.”

• Docker images:

  • openlabfree/hello-hello

  • openlabfree/bye-bye

• Namespace: dev

---

App Source Code (Hello)

from flask import Flask
import socket
import os

app = Flask(__name__)

@app.route("/")
def index():
    return f"""
    <h1>Hello! Nice to meet you!</h1>
    <h3>POD Info</h3>
    Hostname: {socket.gethostname()}<br>
    <h3>Service Info</h3>
    SERVICE_NAME: {os.environ.get('SERVICE_NAME', 'N/A')}<br>
    <h3>Deployment Info</h3>
    DEPLOYMENT: hello-deploy<br>
    """

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

App Source Code (Bye)

from flask import Flask
import socket
import os

app = Flask(__name__)

@app.route("/")
def index():
    return f"""
    <h1>Bye! See you.</h1>
    <h3>POD Info</h3>
    Hostname: {socket.gethostname()}<br>
    <h3>Deployment Info</h3>
    DEPLOYMENT: bye-deploy<br>
    <h3>Service Info</h3>
    SERVICE_NAME: {os.environ.get('SERVICE_NAME', 'N/A')}<br>
    """

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

Dockerfile

FROM python:3.10-slim

WORKDIR /app

COPY app.py .

RUN pip install flask

EXPOSE 5000

CMD ["python", "app.py"]

--- ## First of all, install NGINX Ingress

kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/main/deploy/static/provider/cloud/deploy.yaml

Verify if ingress controller is running

kubectl get pods -n ingress-nginx
kubectl get svc -n ingress-nginx

Patch ingress controller to NodePort type, optionally you can fix the port

kubectl patch svc ingress-nginx-controller \
  -n ingress-nginx \
  -p '{"spec": {"type": "NodePort", "ports":[{"port":80,"targetPort":80,"nodePort":30333,"protocol":"TCP","name":"http"}]}}'

Patch Command (HTTP + HTTPS fixed ports)

kubectl patch svc ingress-nginx-controller \
  -n ingress-nginx \
  -p '{
    "spec": {
      "type": "NodePort",
      "ports": [
        {
          "name": "http",
          "protocol": "TCP",
          "port": 80,
          "targetPort": 80,
          "nodePort": 30333
        },
        {
          "name": "https",
          "protocol": "TCP",
          "port": 443,
          "targetPort": 443,
          "nodePort": 30334
        }
      ]
    }
  }'

Scenario 1: WRONG Label

`label-conflict-demo.yaml`

apiVersion: v1
kind: Namespace
metadata:
  name: dev
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-deploy
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: hello
        image: openlabfree/hello-hello
        env:
        - name: SERVICE_NAME
          value: "hello-service"
        ports:
        - containerPort: 5000
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: bye-deploy
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: bye
        image: openlabfree/bye-bye
        env:
        - name: SERVICE_NAME
          value: "bye-service"
        ports:
        - containerPort: 5000
---
apiVersion: v1
kind: Service
metadata:
  name: hello-service
  namespace: dev
spec:
  selector:
    app: web
  ports:
  - port: 80
    targetPort: 5000
---
apiVersion: v1
kind: Service
metadata:
  name: bye-service
  namespace: dev
spec:
  selector:
    app: web
  ports:
  - port: 80
    targetPort: 5000
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: demo-ing
  namespace: dev
spec:
  rules:
  - host: hello.xyz
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-service
            port:
              number: 80
  - host: bye.xyz
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: bye-service
            port:
              number: 80

Apply it ```bash kubectl apply -f label-conflict-demo.yaml

### Test
Browser access:
```bash
http://hello.xyz:30333
http://bye.xyz:30333

Or with curl:

curl -H "Host: hello.xyz" http://NODE-IP:30333
curl -H "Host: bye.xyz"   http://NODE-IP:30333

Scenario 2: Correct Label

`label-correct-demo.yaml`

apiVersion: v1
kind: Namespace
metadata:
  name: dev
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-deploy
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: hello
  template:
    metadata:
      labels:
        app: hello
    spec:
      containers:
      - name: hello
        image: openlabfree/hello-hello
        env:
        - name: SERVICE_NAME
          value: "hello-service"
        ports:
        - containerPort: 5000
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: bye-deploy
  namespace: dev
spec:
  replicas: 2
  selector:
    matchLabels:
      app: bye
  template:
    metadata:
      labels:
        app: bye
    spec:
      containers:
      - name: bye
        image: openlabfree/bye-bye
        env:
        - name: SERVICE_NAME
          value: "bye-service"
        ports:
        - containerPort: 5000
---
apiVersion: v1
kind: Service
metadata:
  name: hello-service
  namespace: dev
spec:
  selector:
    app: hello
  ports:
  - port: 80
    targetPort: 5000
---
apiVersion: v1
kind: Service
metadata:
  name: bye-service
  namespace: dev
spec:
  selector:
    app: bye
  ports:
  - port: 80
    targetPort: 5000
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: demo-ing
  namespace: dev
spec:
  rules:
  - host: hello.xyz
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-service
            port:
              number: 80
  - host: bye.xyz
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: bye-service
            port:
              number: 80

Apply it: ```bash kubectl apply -f label-correct-demo.yaml

## Test 
Browser access:
```bash
http://hello.xyz:30333
http://bye.xyz:30333

Or with curl:

curl -H "Host: hello.xyz" http://NODE-IP:30333
curl -H "Host: bye.xyz"   http://NODE-IP:30333