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Persistent Volume Claims for Serving

Some serverless applications need permanent data storage. To achieve this, you can configure persistent volume claims (PVCs) for your Knative services.

Enabling PVC support

Procedure

  1. To enable Knative Serving to use PVCs and write to them, modify the KnativeServing custom resource (CR) to include the following YAML:

    Enabling PVCs with write access
    ...
spec:
  config:
    features:
      "kubernetes.podspec-persistent-volume-claim": enabled
      "kubernetes.podspec-persistent-volume-write": enabled
...

    • The kubernetes.podspec-persistent-volume-claim extension controls whether persistent volumes (PVs) can be used with Knative Serving.

    • The kubernetes.podspec-persistent-volume-write extension controls whether PVs are available to Knative Serving with the write access.

  2. To claim a PV, modify your service to include the PV configuration. For example, you might have a persistent volume claim with the following configuration:

    Use the storage class that supports the access mode that you are requesting. For example, you can use the ocs-storagecluster-cephfs class for the ReadWriteMany access mode.
    PersistentVolumeClaim configuration
    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: example-pv-claim
  namespace: my-ns
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: ocs-storagecluster-cephfs
  resources:
    requests:
      storage: 1Gi

    In this case, to claim a PV with write access, modify your service as follows:

    Knative service PVC configuration
    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  namespace: my-ns
...
spec:
 template:
   spec:
     containers:
         ...
         volumeMounts: (1)
           - mountPath: /data
             name: mydata
             readOnly: false
     volumes:
       - name: mydata
         persistentVolumeClaim: (2)
           claimName: example-pv-claim
           readOnly: false (3)
    1 Volume mount specification.
    2 Persistent volume claim specification.
    3 Flag that enables read-only access.

    To successfully use persistent storage in Knative services, you need additional configuration, such as the user permissions for the Knative container user.

Additional resources for OpenShift Container Platform