OpenShift Shared Resource CSI Driver

The OpenShift Shared Resource CSI Driver allows Secrets and ConfigMaps to be shared across Kubernetes namespaces in a controlled manner. This CSI driver ensures that the entity (ServiceAccount) accessing the shared Secret or ConfigMap has permission to do so before mounting the data as a volume into the requesting Pod.

This CSI driver only supports the Ephemeral volume lifecycle mode. It also requires the following during operation:

• podInfoOnMount: true
• fsGroupPolicy: File
• attachRequired: false

Getting Started

The easiest way to use the Shared Resource CSI Driver is to deploy OpenShift v4.10 or higher, and enable the Tech Preview Features.

How To Use

Typically there are two individuals/personas involved when sharing resources:

• A "resource owner" - a platform engineer or other person granted the admin role in multiple application namespaces. This could also be a cluster administrator.
• A "resource consumer" - an application developer who is granted the edit role in a namespace.

Sharing resources is done as follows:

1. The resource owner creates a Secret or ConfigMap to be shared in a "source" namespace. This could also be created by a controller or other system component.

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: shared-config
     namespace: test-share-source # This can be any desired "source" namespace
   data:
     config.txt: "Hello world!"

2. The resource owner creates a corresponding SharedSecret or SharedConfigMap instance to make the resource shareable. The resource owner should also create a ClusterRole that grants subjects permission to use the referenced shared resource.

   ---
   apiVersion: sharedresource.openshift.io/v1alpha1
   kind: SharedConfigMap
   metadata:
     name: share-test-config
   spec:
     configMapRef:
       name: shared-config
       namespace: test-share-source # The "source" namespace"
   ---
   apiVersion: rbac.authorization.k8s.io/v1
   kind: ClusterRole
   metadata:
     name: shared-configmap-use-share-test-config
   rules:
     - apiGroups:
         - sharedresource.openshift.io
       resources:
         - sharedconfigmaps
       resourceNames:
         - share-test-config
       verbs:
         - use

3. The resource owner then creates a Role and RoleBinding in the source namespace that grants the Shared Resource CSI driver permission to read and watch the referenced ConfigMap:

   ---
   apiVersion: rbac.authorization.k8s.io/v1
   kind: Role
   metadata:
     name: shared-test-config
     namespace: test-share-source # This is the source namespace
   rules:
     - apiGroups: [""]
       resources: ["configmaps"]
       resourceNames: ["shared-config"]
       verbs: ["get", "list", "watch"]
   ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: RoleBinding
    metadata:
      name: shared-test-config
      namespace: test-share-source # This is the source namespace
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: Role
      name: shared-test-config
    subjects:
      # The service account for the Shared Resource CSI driver DaemonSet must be listed here.
      # When deployed with Builds for OpenShift, the service account name is
      # `csi-driver-shared-resource`, and the namespace is the same one where the Builds for
      # OpenShift operator is deployed.
      - kind: ServiceAccount
        name: csi-driver-shared-resource
        namespace: openshift-builds

4. Finally, the resource owner grants the desired SeviceAccount in the "target" namespace permission to use the shared resource above:

   ---
   apiVersion: rbac.authorization.k8s.io/v1
   kind: RoleBinding
   metadata:
     name: use-shared-config
     namespace: app-namespace
   roleRef:
     apiGroup: rbac.authorization.k8s.io
     kind: ClusterRole
     name: use-shared-config
   subjects:
     - kind: ServiceAccount
       name: default # or other ServiceAccount specific to the application
       namespace: app-namespace # This is the "target" namespace

5. The resource consumer mounts the shared resource into a Pod (or other resource that accepts CSI Volumes):

   apiVersion: v1
   kind: Pod
   metadata:
     name: example-shared-config
     namespace: app-namespace
   spec:
     ...
     serviceAccountName: default
     volumes:
       - name: shared-config
         csi:
           readOnly: true # required to be true
           driver: csi.sharedresource.openshift.io
           volumeAttributes:
             sharedConfigMap: share-test-config # This must match the name of the SharedConfigMap

See also:

• Simple example
• Tekton example
• OpenShift BuildConfig example

Features

• ServiceAccounts must have the use permission to mount the respective SharedSecret or SharedConfigMap. Volumes fail to mount otherwise - see FAQ for more details.
• Automatic sync of the shared resource data (Secret/ConfigMap) into the mounting Pod.
• Automatic removal/restoration of shared resource data if the Pod's RBAC permissions change at runtime.
• Automatic removal/restoration of shared resource data if the backing Secret/ConfigMap is deleted/re-created.
• Survival of shared resource data with CSI driver restarts/upgrades.
• Multiple SharedSecret/SharedConfig volumes within a Pod. Also supports nested volume mounts within a container.
• Reserve a cluster-scoped share name to a specific Secret or ConfigMap.

The following CSI interfaces are implemented:

• Identity Service: GetPluginInfo, GetPluginCapabilities, Probe
• Node Service: NodeGetInfo, NodeGetCapabilities, NodePublishVolume, NodeUnpublishVolume
• Controller Service: not implemented.

NOTE: see CSI Volume Specifics for restrictions around these features for read-only Volumes.

FAQ

Please refer to the FAQ Guide for commonly asked questions.

Development

See the development guide on how to build and test locally.