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🗂️ Kubernetes Volume Types Comparison

Repository YAML Files:

k8s/labs/storage/emptydir.yaml — Pod with an emptyDir volume for ephemeral, pod-local scratch space.
k8s/labs/storage/hostpath.yaml — Pod mounting a path from the node filesystem via hostPath.

📦

emptyDir

🔄 Ephemeral

📍 Pod Scope

⚡ Fast

💾

hostPath

💾 Host Persistent

🖥️ Node Scope

⚠️ Node-Bound

🗄️

PV/PVC

✅ Persistent

🌐 Cluster Scope

🔒 Decoupled

⚙️

ConfigMap

📄 Config Data

📖 Read-Only

🔄 Dynamic

🔐

Secret

🔑 Sensitive Data

📖 Read-Only

🔒 Encoded

Type	Persistence	Scope	Multi-Pod Access	Primary Use Case
emptyDir	Ephemeral	Pod	Within Pod	Temporary cache, scratch space
hostPath	Host-Bound	Node	Same Node Only	Access host logs/files, testing
PV/PVC	Persistent	Cluster	Yes (RWX)	Databases, stateful apps
ConfigMap	Persistent	Cluster	Yes	Non-sensitive configuration
Secret	Persistent	Cluster	Yes	Passwords, tokens, certificates

Persistence Timeline

Storage Chain: StorageClass → PV → PVC → Pod

🎯 Decision Tree: Which Volume Type to Use?

Need temporary data during Pod lifetime? → Use emptyDir
• Shared cache between containers • Temporary processing • Scratch space

Need to access host node files/directories? → Use hostPath
• Access host logs • Testing/debugging • Single-node clusters only

Need persistent storage across Pod restarts? → Use PV/PVC
• Databases • User uploads • Application state

Need to inject configuration data? → Use ConfigMap
• Application config • Environment variables • Non-sensitive settings

Need to store sensitive information? → Use Secret
• Database passwords • API keys • TLS certificates

📦 emptyDir Example

apiVersion: v1
kind: Pod
metadata:
  name: emptydir-example
spec:
  containers:
  - name: app
    image: busybox
    command: ["/bin/sh", "-c"]
    args: ["echo 'Writing to cache' > /data/cache.txt && sleep 3600"]
    volumeMounts:
    - mountPath: "/data"
      name: cache-volume
  - name: sidecar
    image: busybox
    command: ["/bin/sh", "-c"]
    args: ["while true; do cat /data/cache.txt 2>/dev/null; sleep 5; done"]
    volumeMounts:
    - mountPath: "/data"
      name: cache-volume
  volumes:
  - name: cache-volume
    emptyDir: {}  # Deleted when Pod terminates

💾 hostPath Example

apiVersion: v1
kind: Pod
metadata:
  name: hostpath-example
spec:
  containers:
  - name: log-reader
    image: busybox
    command: ["/bin/sh", "-c"]
    args: ["tail -f /host/syslog"]
    volumeMounts:
    - mountPath: "/host"
      name: host-volume
      readOnly: true
  volumes:
  - name: host-volume
    hostPath:
      path: /var/log  # Accesses host node's /var/log
      type: Directory  # Must exist on host

🗄️ PV/PVC Example

---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-example
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce  # RWO, ROX, or RWX
  persistentVolumeReclaimPolicy: Retain
  storageClassName: standard
  hostPath:
    path: /mnt/data
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-example
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: standard
---
apiVersion: v1
kind: Pod
metadata:
  name: pvc-pod
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - mountPath: "/usr/share/nginx/html"
      name: storage
  volumes:
  - name: storage
    persistentVolumeClaim:
      claimName: pvc-example

⚙️ ConfigMap Example

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  app.properties: |
    database.host=db.example.com
    database.port=5432
    log.level=INFO
  ui.json: |
    {
      "theme": "dark",
      "language": "en"
    }
---
apiVersion: v1
kind: Pod
metadata:
  name: configmap-pod
spec:
  containers:
  - name: app
    image: myapp:1.0
    volumeMounts:
    - name: config
      mountPath: "/etc/config"
      readOnly: true
  volumes:
  - name: config
    configMap:
      name: app-config  # Mounts all keys as files

🔐 Secret Example

---
apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  # Base64 encoded values
  username: YWRtaW4=        # 'admin'
  password: cGFzc3dvcmQxMjM=  # 'password123'
---
apiVersion: v1
kind: Pod
metadata:
  name: secret-pod
spec:
  containers:
  - name: app
    image: postgres:13
    env:
    - name: POSTGRES_USER
      valueFrom:
        secretKeyRef:
          name: db-secret
          key: username
    - name: POSTGRES_PASSWORD
      valueFrom:
        secretKeyRef:
          name: db-secret
          key: password
    volumeMounts:
    - name: secret-volume
      mountPath: "/etc/secrets"
      readOnly: true
  volumes:
  - name: secret-volume
    secret:
      secretName: db-secret  # Also mountable as files