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: default # This can be any desired "source" namespace
   data:
     config.txt: "Hello world!"

2. The resource owner creates a SharedSecret or SharedConfigMap instance to make the resource shareable:

   apiVersion: sharedresource.openshift.io/v1alpha1
   kind: SharedConfigMap
   metadata:
     name: share-default-config
   spec:
     configMapRef:
       name: shared-config
       namespace: default

3. 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: Role
   metadata:
     name: use-shared-default-config
     namespace: app-namespace # This is the "target" namespace
   rules:
     - apiGroups:
         - sharedresource.openshift.io
       resources:
         - sharedconfigmaps
       resourceNames:
         - share-default-config
       verbs:
         - use
   ---
   apiVersion: rbac.authorization.k8s.io/v1
   kind: RoleBinding
   metadata:
     name: use-shared-default-config
     namespace: app-namespace
   roleRef:
     apiGroup: rbac.authorization.k8s.io
     kind: Role
     name: use-shared-default-config
   subjects:
     - kind: ServiceAccount
       name: default
       namespace: app-namespace

4. 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-default-config

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.