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Storage in Kubernetes

Store application state and exchange it between Pods with Kubernetes.

Volumes

A volume can be used to hold data and state for a container. A pod cna have multiple volumes. Containers rely on a mountPath to access a volume.

A volume references a storage location. Must have a unique name. Attached to a pod and may or may not tied to the pods lifetime depending on the type of storage.

PersistentVolume PersistentVolumeClaim StorageClass

Volume Types

  • emptyDir - Stores transient data (shares a pod's lifetime)

  • hostPath - Pod mounts into the node's filesystem

  • nfs - An NFS share from the network mounted on the Pod

  • configMap/secret
  • persistentVolumeClaim - provides pods with a more persistent storage option
  • Cloud

Host Path

Can access various different types of resources on the server based on file access.

  • DirectoryOrCreate
  • Directory
  • FileOrCreate
  • File
  • Socket
  • CharDevice
  • BlockDevice ... etc ...

Kubectl

The describe command will list the volumes for the pod.

kubectl describe pod [pod-name]

PersistentVolume

A cluster-wide storage resource that relies on network-attached storage. Normally provisioned by a cluster administrator. Available to a Pod even if it gets rescheduled to a different Node. Rely on a storage provider such as NFS, cloud storage, or other options.

PersistentVolumeClaim - claims the storage so that a Pod can use it.

Process

  1. Create a network storage resource (NFS, cloud, etc)
  2. Define a persistent volume that links kubernetes to the storage
  3. Create a PVC which links the pod to the persistent volume.

YAML

GitHub site with lots of examples:

TODO: Add it here...

Storage Class

Sets up to automatically provision persistent volumes.

  1. Create Storage Class
  2. Create a PVC that references a storage class
  3. Persistent Volume is automatically created
  4. PV is automatically bound
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