Working with Volumes

1. Using emptyDir Volumes

Property	Value	Description
emptyDir	`{}`	Defines an emptyDir volume
medium	`""` or `"Memory"`	Storage medium: "" for disk, "Memory" for RAM
sizeLimit	`1Gi`	Maximum size of the volume (optional)

Example: Mounting an emptyDir Volume

apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
  - name: test-container
    image: nginx
    volumeMounts:
    - name: cache-volume
      mountPath: /cache
  volumes:
  - name: cache-volume
    emptyDir: {}

Note: Data in emptyDir volumes is lost when the Pod is deleted.

Warning: Using medium: Memory can lead to memory pressure on nodes.

2. Using hostPath Volumes

Property	Value	Description
hostPath.path	`/var/lib/data`	Path on the host node filesystem to mount
hostPath.type	`Directory`	Optional field to specify type of path (Directory, File, etc.)

Example: Mounting hostPath volume in Pod

apiVersion: v1
kind: Pod
metadata:
  name: hostpath-pod
spec:
  containers:
  - name: app-container
    image: nginx
    volumeMounts:
    - name: host-data
      mountPath: /usr/share/nginx/html
  volumes:
  - name: host-data
    hostPath:
      path: /var/lib/data
      type: Directory

Note: Using hostPath volumes can pose security risks and should be used carefully in production environments.

3. Configuring PersistentVolumes

Property	Description	Values	Notes
capacity	Storage size of the volume	`10Gi`, `500Mi`	Must be specified for all volumes
accessModes	How the volume can be mounted	`ReadWriteOnce`, `ReadOnlyMany`, `ReadWriteMany`	Must include at least one mode
persistentVolumeReclaimPolicy	What happens after the PVC is deleted	`Retain`, `Recycle`, `Delete`	`Retain` is default in most cases
storageClassName	Storage class to use for dynamic provisioning	`standard`, `fast`	Optional; if omitted, uses default class
volumeMode	Volume mode (file or block)	`Filesystem`, `Block`	Defaults to `Filesystem`

Example: Creating a PersistentVolume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-example
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: standard
  hostPath:
    path: /mnt/data

Note: hostPath is for testing only. In production, use cloud provider or CSI drivers.

Warning: Ensure accessModes match the application's needs to avoid runtime errors.

4. Creating PersistentVolumeClaims

Field	Description	Example
apiVersion	API version to use	`corev1`
kind	Resource type	`PersistentVolumeClaim`
metadata.name	Name of the PVC	`my-pvc`
spec.accessModes	Access mode for volume	`[ReadWriteOnce]`
spec.resources.requests.storage	Storage size requested	`10Gi`
spec.storageClassName	Storage class to use (optional)	`standard`

Example: Creating a PVC

apiVersion: corev1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

5. Binding PVC to PV

Property	Description	Values
claimRef	Reference to the PersistentVolumeClaim	`object`
persistentVolumeReclaimPolicy	Policy for reclaiming the volume after the claim is released	`Delete`, `Retain`
storageClassName	Storage class name for dynamic provisioning	`standard`, `fast`

Example: Binding PVC to PV

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  volumeName: my-pv

Note: The volumeName must match the name of an existing PersistentVolume.

Warning: Ensure that the storageClassName matches between PVC and PV for dynamic provisioning.

6. Listing PersistentVolumes

Field	Description	Example Value
metadata.name	Name of the PersistentVolume	`pv0001`
spec.capacity	Storage capacity of the volume	`5Gi`
spec.accessModes	Access modes supported by the volume	`["ReadWriteOnce"]`
spec.persistentVolumeReclaimPolicy	Policy for reclaiming the volume	`Retain`
spec.storageClassName	StorageClass associated with the volume	`standard`
status.phase	Current phase of the volume (e.g., Available, Bound)	`Available`

Example: Listing PersistentVolumes using kubectl

kubectl get persistentvolumes

Example: Listing PersistentVolumes with detailed output

kubectl get persistentvolumes -o wide

Example: Listing PersistentVolumes in JSON format

kubectl get persistentvolumes -o json

7. Listing PersistentVolumeClaims

Field	Description	Example Value
metadata.name	Name of the PVC	`my-pvc`
spec.accessModes	Access mode for the volume	`["ReadWriteOnce"]`
spec.resources.requests.storage	Requested storage size	`10Gi`
status.phase	Current phase of the PVC	`Pending`

Example: List PVCs in a Namespace

kubectl get pvc -n my-namespace

Example: List All PVCs in the Cluster

kubectl get pvc --all-namespaces

Example: Describe a Specific PVC

kubectl describe pvc my-pvc -n my-namespace

8. Understanding Access Modes

Mode	Description	Usage
ReadWriteOnce (RWO)	Volume can be mounted as read-write by a single node	Most common for single pod usage
ReadOnlyMany (ROX)	Volume can be mounted as read-only by many nodes	Use for shared read-only data like config maps or images
ReadWriteMany (RWX)	Volume can be mounted as read-write by many nodes	Requires underlying storage to support concurrent writes (e.g., NFS)

Note: Not all storage systems support all access modes. Ensure your storage class supports the desired mode.

9. Setting Reclaim Policies

Policy	Description	Behavior	Use Case
Retain	Volume is not deleted when the PVC is deleted	Manual cleanup required	For data preservation, backup scenarios
Recycle	Deprecated in Kubernetes 1.5+, replaced by `Retain`	Basic cleanup using a simple command	Legacy systems only (not recommended)
Delete	Volume is deleted when the PVC is deleted	Automatic cleanup of storage	Temporary or ephemeral data storage

Example: Setting Reclaim Policy to Retain

apiVersion: v1
kind: PersistentVolume
metadata:
  name: example-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: /mnt/data

Note: The Retain policy allows manual cleanup of volumes, useful for data recovery or backup scenarios.

Warning: Using Recycle policy is deprecated and should not be used in production.

10. Using Dynamic Provisioning

Property	Description	Default Value	Notes
storageClassName	Name of the StorageClass to use for dynamic provisioning	""	Must match an existing StorageClass name in the cluster
volumeName	Name of the volume to be created (optional)	""	If not specified, a unique name is generated
accessModes	Access modes for the volume (e.g., ReadWriteOnce, ReadOnlyMany)	[ReadWriteOnce]	Must be supported by the StorageClass
resources.requests.storage	Requested storage size (e.g., 10Gi)	None	Must be specified for dynamic provisioning

Example: Creating a PersistentVolumeClaim with Dynamic Provisioning

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dynamic-pvc
spec:
  storageClassName: "fast-ssd"
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi

Note: The storageClassName must reference a valid StorageClass that supports dynamic provisioning.

Warning: Ensure the StorageClass has sufficient capacity and appropriate provisioner to handle the requested storage size.

11. Expanding PersistentVolumes

Field	Description	Notes
spec.capacity	Requested storage capacity	Must be greater than current size
spec.accessModes	Access modes for volume	Must include existing mode(s)
spec.volumeName	Name of the volume to expand	Must match existing PV name

Example: Expanding a PersistentVolume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: example-pv
spec:
  capacity:
    storage: 50Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  csi:
    driver: ebs.csi.aws.com
    volumeHandle: vol-0123456789abcdef0

Note: Expansion is only supported for volumes that are not currently in use by a pod.

Warning: Ensure that the underlying storage system supports expansion before attempting to increase capacity.

Key Points

Expansion requires allowVolumeExpansion to be enabled in the StorageClass.
Only ReadWriteOnce and ReadWriteMany access modes support expansion.
Expanding a volume does not affect data or existing mounts.

12. Deleting PersistentVolumeClaims

Property	Description	Notes
persistentVolumeClaim.name	Name of the PersistentVolumeClaim to delete	Must match existing PVC name
persistentVolumeClaim.namespace	Namespace where PVC is defined	Defaults to current namespace if not specified

Example: Delete PVC using kubectl

kubectl delete pvc my-pvc -n my-namespace

Note: Deleting a PVC will also delete the associated PersistentVolume if reclaimPolicy is set to Delete.

Warning: Ensure data is backed up before deletion as this action is irreversible.