https://drive.google.com/file/d/1-3S5P8ol2oSQfaSaHRDfWMwdO58tk5TX/view?usp=sharing

🔍 YAML Breakdown

apiVersion: v1
kind: Pod
metadata:
  name: probeone
  labels:
    app: apache
spec:
  containers:
  - name: boxone
    image: lovelearnlinux/webserver:v1
    ports:
    - containerPort: 80
    readinessProbe:
      tcpSocket:
        port: 80            # ← Check if TCP port 80 is open
      initialDelaySeconds: 5
      periodSeconds: 10
    livenessProbe:
      tcpSocket:
        port: 80            # ← Same check, different purpose
      initialDelaySeconds: 15
      periodSeconds: 20

🔑 Key Insight:

Both probes check the same TCP port, but they serve completely different purposes.

📌 Readiness vs Liveness: The Critical Difference

🎯 Your Configuration:

• Readiness: Starts after 5s, checks every 10s → fast traffic control
• Liveness: Starts after 15s, checks every 20s → slower auto-healing

💡 Why tcpSocket?

• Simpler than httpGet for basic connectivity
• Works for any TCP service (not just HTTP)

🧪 k3s Lab: Observe Both Probes in Action

🔧 Step 1: Deploy Pod + Service

💡 We need a Service to see readiness in action.

# 1. Save Pod YAML as pod-probes.yaml
kubectl apply -f pod-probes.yaml

# 2. Create Service
kubectl expose pod probeone --port=80 --target-port=80

# 3. Verify
kubectl get pods,svc

🔧 Step 2: Test Readiness (Simulate Startup Delay)

💡 Block port 80 temporarily to simulate app not ready:

# On the Pod, block port 80 (simulate app startup)
kubectl exec probeone -- iptables -A INPUT -p tcp --dport 80 -j DROP

# Watch Endpoints (should become <none>)
kubectl get endpoints probeone -w
# NAME       ENDPOINTS   AGE
# probeone   <none>      5s  ← REMOVED FROM SERVICE!

# Test connectivity (should fail)
kubectl run debug --image=curlimages/curl -it --rm -- sh
# curl <http://probeone>  ← Connection refused

🔧 Step 3: Restore Readiness

# Unblock port 80
kubectl exec probeone -- iptables -D INPUT -p tcp --dport 80 -j DROP

# Watch Endpoints return
kubectl get endpoints probeone -w
# NAME       ENDPOINTS         AGE
# probeone   10.42.0.10:80     10s  ← BACK IN SERVICE!

# Test connectivity (should work)
curl <http://probeone>  # ✅ Welcome page

🔧 Step 4: Test Liveness (Simulate App Crash)