Getting started with durable storage¶

App storage generally falls into one of two categories:

Ephemeral or stateless
Persistent, or stateful

If your app's main concern is transactional processing, it is likely a good candidate for simple, ephemeral storage. If your app needs to reload data to start, or makes use of a database, it is likely better to use persistent storage.

Ephemeral storage¶

Storage that is configured as an emptyDir creates a temporary volume that the pod can use.

Warning

emptyDir storage is lost if the pod restarts

Similar to secrets, we configure storage in the Helm chart values.yaml file.

...
frontend:
...
  # -- volumeMounts for the frontend container that also create corresponding `emptyDir` volumes in the pod.
  # @default -- `[{name: tmp, mountPath: /tmp}]`
  emptyDirMounts:
    - name: tmp
      mountPath: /tmp
...

This generates a resource manifest with a volumeMount configuration:

...
apiVersion: apps/v1
kind: Deployment
...
spec:
  template:
    spec:
      containers:
        - volumeMounts:
            - name: "tmp"
              mountPath: "/tmp"
...
      volumes:
        - name: "tmp"
          emptyDir: {}
...

Persistent storage¶

Apps that need dedicated storage - either to avoid a loss of data when a pod restarts, or because the types of files used by the container are large binaries - can configure persistent volumes. Persistent volumes are configured in the Helm chart values.yaml file, and volumes are provisioned by the Longhorn storage operator.

...
frontend:
...
  # Configuration for persistent volume claims
  # @default -- `[]`
  storageMounts:
    - name: api-data-storage
      size: 10Gi
      # -- Location where the PVC will be mounted.
      mountPath: "/app/data"
      # -- Name of the storage class to use. If null it will use the
      # configured default Storage Class.
      storageClass: null
      # -- Access Mode of the storage device being used for the PVC
      accessMode: ReadWriteOnce
...

This generates a resource manifest with a volumeMount configuration:

...
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
        - volumeMounts:
            - name: api-data-storage
              mountPath: /app/data
...
      volumes:
        - name: api-data-storage
          persistentVolumeClaim:
            claimName: api-data-storage
...