Kubernetes Storage – Persistent Volumes and StorageClasses

Kubernetes provides a powerful storage system to ensure data persistence for containerized applications. Since Pods are ephemeral and can be deleted or restarted anytime, Kubernetes uses Persistent Volumes (PV) and Persistent Volume Claims (PVC) to manage storage efficiently.

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🔌 Understanding Kubernetes Storage

✅ Ephemeral Storage – Data stored inside a Pod is lost when the Pod is deleted.
✅ Persistent Storage – Data remains even if the Pod is restarted or moved.
✅ Persistent Volumes (PV) – A storage resource provisioned in the cluster.
✅ Persistent Volume Claims (PVC) – A request from a Pod to use a PV.
✅ StorageClass – Defines different types of storage (e.g., SSD, HDD, cloud storage).

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🏗 Key Kubernetes Storage Concepts

1️⃣ Ephemeral Storage – Pod-Level Storage

Kubernetes provides emptyDir and hostPath for temporary storage.

🔹 emptyDir – Temporary Storage Inside Pods

• Deleted when the Pod is removed.
• Useful for caching or temporary files.

yaml

apiVersion: v1
kind: Pod
metadata:
  name: temp-storage-pod
spec:
  containers:
    - name: busybox
      image: busybox
      command: [ "sleep", "3600" ]
      volumeMounts:
        - mountPath: "/cache"
          name: cache-volume
  volumes:
    - name: cache-volume
      emptyDir: {}

🔹 hostPath – Access Host System Storage

• Used for accessing node’s file system.
• Not recommended for multi-node clusters.

yaml

apiVersion: v1
kind: Pod
metadata:
  name: host-storage-pod
spec:
  containers:
    - name: busybox
      image: busybox
      command: [ "sleep", "3600" ]
      volumeMounts:
        - mountPath: "/data"
          name: host-volume
  volumes:
    - name: host-volume
      hostPath:
        path: "/mnt/data"

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2️⃣ Persistent Volumes (PV) – Cluster-Level Storage

A Persistent Volume (PV) is a cluster-wide storage resource that provides storage to Pods. It supports multiple storage backends like NFS, AWS EBS, Azure Disks, GCE Persistent Disks, and more.

🔹 Creating a Persistent Volume (PV)

yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: my-pv
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: "/mnt/k8s-data"

PV Access Modes:

Access Mode	Description
ReadWriteOnce (RWO)	One node can read & write.
ReadOnlyMany (ROX)	Multiple nodes can read.
ReadWriteMany (RWX)	Multiple nodes can read & write.

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3️⃣ Persistent Volume Claims (PVC) – Requesting Storage

A Persistent Volume Claim (PVC) is a request for storage from a Persistent Volume (PV).

🔹 Creating a Persistent Volume Claim (PVC)

yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi
  storageClassName: manual

🔹 Using a PVC in a Pod

yaml

apiVersion: v1
kind: Pod
metadata:
  name: my-pvc-pod
spec:
  containers:
    - name: busybox
      image: busybox
      command: [ "sleep", "3600" ]
      volumeMounts:
        - mountPath: "/data"
          name: storage
  volumes:
    - name: storage
      persistentVolumeClaim:
        claimName: my-pvc

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4️⃣ StorageClass – Dynamic Storage Provisioning

Instead of manually creating PVs, StorageClasses allow dynamic volume provisioning.

🔹 Creating a StorageClass for AWS EBS

yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: aws-ebs
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
  fsType: ext4

🔹 Creating a PVC That Uses StorageClass

yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dynamic-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: aws-ebs

📌 When this PVC is created, Kubernetes will automatically provision an AWS EBS volume.

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🔄 Troubleshooting Kubernetes Storage

🔹 Check Persistent Volumes (PV)

kubectl get pv
kubectl describe pv my-pv

🔹 Check Persistent Volume Claims (PVC)

kubectl get pvc
kubectl describe pvc my-pvc

🔹 Check StorageClasses

kubectl get storageclass
kubectl describe storageclass aws-ebs

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🏆 Summary – Kubernetes Storage at a Glance

Concept	Purpose
emptyDir	Temporary storage for a Pod (deleted when Pod stops).
hostPath	Accesses node’s storage (tied to specific node).
Persistent Volume (PV)	Pre-provisioned cluster-wide storage resource.
Persistent Volume Claim (PVC)	Request for storage from a PV.
StorageClass	Enables dynamic storage provisioning.

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📢 Next Up: Kubernetes Deployments – Scaling and Rolling Updates with ReplicaSets!