Storage Provisioner in K8

In Kubernetes, a storage provisioner is responsible for dynamically provisioning storage resources for pods as they are needed. It automates the process of creating storage volumes, saving administrators from manually managing storage for each workload. Here’s how it works:

Key Tasks of a Storage Provisioner

Dynamic Volume Creation

• Based on a PersistentVolumeClaim (PVC) created by a pod, the provisioner automatically creates a corresponding PersistentVolume (PV) using the defined StorageClass.
• The provisioner determines the type of storage (e.g., block, file) and its attributes (e.g., size, IOPS).

Binding PVCs to PVs

• The provisioner ensures that the requested PVC is bound to the newly created PV, making it ready for use by the pod.

Backend Integration

• Provisioners communicate with external storage backends (e.g., AWS EBS, GCE Persistent Disks, NFS, or Ceph) to allocate resources.
• They use the parameters defined in the StorageClass to interact with the storage provider.

Access Mode Management

• The provisioner ensures the correct access modes (e.g., ReadWriteOnce, ReadOnlyMany, ReadWriteMany) are honored based on the PVC specification.

Lifecycle Management

• Depending on the reclaim policy of the PersistentVolume (e.g., Delete or Retain), the provisioner might delete the storage resource when the PVC is deleted or retain it for manual reuse.

Error Handling and Reporting

• If provisioning fails (e.g., insufficient capacity), the provisioner provides feedback through the PVC status, enabling users to troubleshoot issues.

Built-in vs. External Provisioners

• Built-in Provisioners: Managed by Kubernetes, typically for cloud providers (e.g., kubernetes.io/aws-ebs, kubernetes.io/gce-pd).
• External Provisioners: Operate as out-of-tree controllers for custom or advanced storage solutions (e.g., csi-provisioner for CSI drivers).

Example Flow:

1. User creates a PVC requesting 50Gi of storage with a specific StorageClass.
2. The provisioner linked to the StorageClass creates a PV of 50Gi from the backend storage system.
3. The PVC is automatically bound to the PV.
4. The pod mounts the PV and uses it as persistent storage.

This abstraction simplifies storage management while ensuring scalability and flexibility for dynamic workloads.