Project: Understanding Kubernetes Volume Types

🎯 Goal

By the end, you will viscerally know:

• why some data disappears
• why some data survives pod restarts
• when to use each volume
• why databases require PVCs

---

🧠 The 3 volume types we will test

Volume	Data survives pod restart?	Use case
emptyDir	❌ NO	temp files, cache
hostPath	⚠️ SOMETIMES	node-specific (dangerous)
PVC	✅ YES	databases, user data

---

📁 Project structure

k8s-volumes-lab/
├── emptydir.yaml
├── hostpath.yaml
├── pvc.yaml
└── pod-pvc.yaml

---

🧩 PART 1 — emptyDir (DATA DIES WITH POD)

📄 emptydir.yaml

apiVersion: v1
kind: Pod
metadata:
  name: emptydir-demo
spec:
  containers:
    - name: app
      image: busybox
      command: ["sh", "-c", "sleep 3600"]
      volumeMounts:
        - name: data
          mountPath: /data
  volumes:
    - name: data
      emptyDir: {}

▶️ Apply

kubectl apply -f emptydir.yaml
kubectl exec -it emptydir-demo -- sh

✍️ Create data

echo "HELLO FROM EMPTYDIR" > /data/file.txt
cat /data/file.txt

❌ Kill the pod

kubectl delete pod emptydir-demo
kubectl apply -f emptydir.yaml
kubectl exec -it emptydir-demo -- cat /data/file.txt

💥 Result

No such file or directory

🧠 Lesson

emptyDir lives only as long as the pod lives

---

🧩 PART 2 — hostPath (DATA TIED TO NODE)

📄 hostpath.yaml

apiVersion: v1
kind: Pod
metadata:
  name: hostpath-demo
spec:
  containers:
    - name: app
      image: busybox
      command: ["sh", "-c", "sleep 3600"]
      volumeMounts:
        - name: host
          mountPath: /data
  volumes:
    - name: host
      hostPath:
        path: /tmp/hostpath-demo
        type: DirectoryOrCreate

▶️ Apply

kubectl apply -f hostpath.yaml
kubectl exec -it hostpath-demo -- sh

✍️ Create data

echo "HELLO FROM HOSTPATH" > /data/file.txt

🔁 Restart pod

kubectl delete pod hostpath-demo
kubectl apply -f hostpath.yaml
kubectl exec -it hostpath-demo -- cat /data/file.txt

✅ Result

HELLO FROM HOSTPATH

⚠️ Why this is dangerous

• Data exists only on one node
• Pod moves → data gone
• Breaks HA
• NEVER use for DBs in prod

🧠 Lesson

hostPath is node-coupled, not cluster-safe

---

🧩 PART 3 — PVC (PRODUCTION-SAFE STORAGE)

📄 pvc.yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: demo-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

📄 pod-pvc.yaml

apiVersion: v1
kind: Pod
metadata:
  name: pvc-demo
spec:
  containers:
    - name: app
      image: busybox
      command: ["sh", "-c", "sleep 3600"]
      volumeMounts:
        - name: data
          mountPath: /data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: demo-pvc

▶️ Apply

kubectl apply -f pvc.yaml
kubectl apply -f pod-pvc.yaml
kubectl exec -it pvc-demo -- sh

✍️ Create data

echo "HELLO FROM PVC" > /data/file.txt

🔁 Restart pod

kubectl delete pod pvc-demo
kubectl apply -f pod-pvc.yaml
kubectl exec -it pvc-demo -- cat /data/file.txt

✅ Result

HELLO FROM PVC

🧠 Lesson

PVC survives pod death — this is how databases live

---

🧠 FINAL COMPARISON (MEMORIZE THIS)

Volume	Pod dies	Data
emptyDir	❌	❌
hostPath	❌	⚠️ (node-only)
PVC	❌	✅

---

🔥 WHY DATABASES REQUIRE PVCs

Databases:

• must survive restarts
• must survive rescheduling
• must survive upgrades

PVC gives:

• persistent disk
• node-independent storage
• safe recovery

Without PVC:

Kubernetes is doing exactly what it was designed to do — destroy pods.

---

🖼️ Visual intuition

---

🎯 What a 6-year DevOps engineer says in interviews

“Pods are ephemeral, so persistent data must live on PVCs. emptyDir is for temporary data, hostPath is node-coupled and unsafe in production, and PVC abstracts durable storage from pod lifecycle.”