Abdullah Şamil Güser

Storage & Persistence

Volumes

• We need to store data outside the container in a Volume
• Volumes let containers store data into external storage systems
• Vendors create plugins for their storage systems according to the Container Storage Interface
• Two ways to create storage
  • Static and dynamic

Storage - Static Way

• Persistent Volumes
  • Represent a storage resource
  • Cluster wide
  • Provisioned by an administrator
• Persistent Volume Claim
  • A one-to-one mapping to a persistent volume
• One or more pods can use a Persistent Volume Claim
• Can be consumed by any of the containers within the pod

Reclaim Policy

• Delete
  • Delete the data upon pods deletion
  • The default
• Retain
  • Keeps the data upon pods deletion

Access Modes

• ReadWriteMany
  • The volume can be mounted as read-write by many pods
• ReadOnlyMany
  • The volume can be mounted read-only by many pods
• ReadWriteOnce
  • The volume can be mounted as read-write by a single pod
  • The other pods are in read-only mode
  • The one that has mounted the volume first will be able to write

Persistent Volume States

• Available :A free resource that is not yet bound to a claim
• Bound : The volume is bound to a claim
• Released : The claim has been deleted, but the resource is not yet reclaimed by the cluster
• Failed : The volume has failed its automatic reclamation

kubectl - Persistent Volume Cheat Sheet

# Deploy the PVs and PVCs
kubectl apply -f [definition.yaml]

# Get the PV list
kubectl get pv

# Get the PVC list
kubectl get pvc

# Describe the PV
kubectl describe pv [pvName]

# Describe the PVC
kubectl describe pvc [pvcName]

# Delete the PVs and PVCs
kubectl delete -f [definition.yaml]

# Delete the pv using its name
kubectl delete pv [pvName]

# Delete the pvc using its name
kubectl delete pvc [pvcName]

Storage - Dynamic Way

Storage Class

• Describes the “classes” of storage offered by the admin
• An abstraction on top of an external storage resource
• No need to set a capacity
• Eliminates the need for the admin to pre-provision a persistent volume

Reclaim Policy

• Delete
  • Delete the data upon pods deletion
  • The default
• Retain
  • Keeps the data upon pods deletion

Access Modes

• ReadWriteMany
  • The volume can be mounted as read-write by many pods
• ReadOnlyMany
  • The volume can be mounted read-only by many pods
• ReadWriteOnce
  • The volume can be mounted as read-write by a single pod
  • The other pods are in read-only mode
  • The one that has mounted the volume first will be able to write

kubectl - Storage Class Cheat Sheet

# Deploy the StorageClass or PVC
kubectl apply -f [definition.yaml]

# Get the StorageClass list
kubectl get sc

# Get the PVC list
kubectl get pvc

# Describe the StorageClass
kubectl describe sc [className]

# Delete the SC and PVC
kubectl delete -f [definition.yaml]

# Delete the SC using its name
kubectl delete sc [className]

# Delete the PVC using its name
kubectl delete pvc [pvcName]