21_PersistentVolumeClaim.md

What is PersistentVolumeClain (PVC)?

A PersistentVolumeClaim (PVC) is a request made by a Pod (or user) for storage.

It is the bridge between a Pod and a PersistentVolume (PV).

📌 Pods → PVC → PV → Storage Backend

PVC allows the Pod to ask for:

• Storage size (e.g., 5Gi)
• Access mode (RWO/RWX/ROX)
• StorageClass (optional) Kubernetes then finds a matching PV OR dynamically creates one through StorageClass.

Key Characteristics

1. Acts as a "storage request" PVC specifies:

• Storage size (example: 5Gi)
• Access mode (RWO / RWX / ROX)
• Optional storage class (SSD, HDD, Ceph, EBS, etc.)

PVC does not define the actual backend — it only requests it.

2. Binds to a matching PersistentVolume (PV)

After PVC is created:

• Kubernetes searches for a PV that matches the request
• If found → PVC gets bound to that PV
• If not found → it waits, or provisioning is done dynamically Once bound, a PVC is exclusive to that PV.

3. Supports dynamic provisioning

If a StorageClass is specified:

• Kubernetes automatically creates a PV using the storage provider
• No admin involvement needed Example:

storageClassName: fast-ssd

4. Decouples app from storage tech PVC users (pods) don’t care if storage is:

• NFS
• AWS EBS
• Azure Disk
• GCE PD
• Ceph RBD
• CSI drivers PVC abstracts the backend completely.

5. Namespace-scoped

PVCs live inside namespaces, unlike PVs (cluster-level). Pods must be in the same namespace to use PVC.

PVC YAML Definition

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mypvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

Summary

Property	Description
What is PVC?	A request for persistent storage
Purpose	Allow Pods to consume storage without knowing the backend
Scope	Namespace-scoped
Binds to	A PV (cluster-scoped)
Used For	Databases, StatefulSets, CNFs
Supports	RWO, RWX, ROX
Provisioning	Static or dynamic (via StorageClass)