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Updated KEP-3314 with install instructions for the SnapshotMetadataService CRD #5935

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Updated KEP-3314 with install instructions for the SnapshotMetadataService CRD #5935

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29 changes: 18 additions & 11 deletions keps/sig-storage/3314-csi-changed-block-tracking/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -985,8 +985,8 @@ gRPC service provided by the
[external-snapshot-metadata sidecar](#the-external-snapshot-metadata-sidecar)
deployed by a CSI driver.

The CR name should be that of the associated CSI driver to ensure that only one such
CR is created for a given driver.
Instances of the CR are created by a CSI driver installer and named for the
associated CSI driver, to ensure that only one such CR is created for a given driver.

The CR `spec` contains the following fields:

Expand All @@ -1002,7 +1002,11 @@ The CR `spec` contains the following fields:
presented to the [sidecar](#the-external-snapshot-metadata-sidecar) by a Kubernetes client.
The value should be unique to the service if possible; for example, it could be the DNS name of the service.

The full Custom Resource Definition is shown below:
The `SnapshotMetadataService` Custom Resource Definition should be installed either by the Kubernetes
distribution or by the cluster administrator.
The specification of this CRD at the time of publication of this KEP is shown below;
see [cbt.storage.k8s.io_snapshotmetadataservices.yaml](https://github.com/kubernetes-csi/external-snapshot-metadata/blob/3a139dd44d4ffa01343a91bed40996b1db56fd38/client/config/crd/cbt.storage.k8s.io_snapshotmetadataservices.yaml)
in the source code repository for the latest copy.

```yaml
apiVersion: apiextensions.k8s.io/v1
Expand All @@ -1022,7 +1026,7 @@ spec:
singular: snapshotmetadataservice
scope: Cluster
versions:
- name: v1alpha1
- name: v1beta1
schema:
openAPIV3Schema:
description: 'The presence of a SnapshotMetadataService CR advertises the existence of a CSI
Expand Down Expand Up @@ -1512,16 +1516,19 @@ rollout. Similarly, consider large clusters and how enablement/disablement
will rollout across nodes.
-->

The CSI driver installs the `SnapshotMetadataService` CRD.
Since the `SnapshotMetadataService` CRD is shared between CSI drivers, a
CSI driver should fail if it finds a pre-existing CRD with an incompatible
version and surface the error to the cluster administrator to resolve.
The [SnapshotMetadataService CRD](https://github.com/kubernetes-csi/external-snapshot-metadata/blob/3a139dd44d4ffa01343a91bed40996b1db56fd38/client/config/crd/cbt.storage.k8s.io_snapshotmetadataservices.yaml)
should be installed either by the Kubernetes distribution or by the cluster administrator.
This CRD applies to all the installed CSI drivers that support this feature.

A CSI driver creates an instance of the `SnapshotMetadataService` CR
and deploys the `external-snapshot-metadata` sidecar.
The CSI driver may fail to install or may skip the configuration of this feature
if it finds that the installed `SnapshotMetadataService` CRD has an incompatible
version; it must surface the error for the cluster administrator to resolve
in either circumstance.

The CSI driver creates an instance
of this CR, and deploys the `external-snapshot-metadata` sidecar.
Each CSI driver vendor independently must explicitly handle failure to construct
these objects during rollout or rollback if their driver fails.

Any rollback will cause active operations by a backup application to fail.
Such failure is similar to a network failure that the backup client application ought to be
capable of handling gracefully.
Expand Down