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Documentation on the external-snaphot-metadata sidecar (alpha).
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‎book/src/SUMMARY.md

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- [cluster-driver-registrar](cluster-driver-registrar.md) (deprecated)
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- [external-health-monitor-controller](external-health-monitor-controller.md)
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- [external-health-monitor-agent](external-health-monitor-agent.md)
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- [external-snapshot-metadata](external-snapshot-metadata.md)
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- [CSI objects](csi-objects.md)
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- [CSIDriver Object](csi-driver-object.md)
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- [CSINode Object](csi-node-object.md)
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- [CSI Windows](csi-windows.md)
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- [Volume Mode Conversion](prevent-volume-mode-conversion.md)
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- [Cross-Namespace Data Sources](cross-namespace-data-sources.md)
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- [Changed Block Tracking](changed-block-tracking.md)
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- [Deploying a CSI Driver on Kubernetes](deploying.md)
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- [Example](example.md)
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- [Driver Testing](testing-drivers.md)

‎book/src/changed-block-tracking.md

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# Changed Block Tracking
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## Status
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Status | Min K8s Version | Max K8s Version | external-snapshot-metadata Version
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-------|-----------------|-----------------|-----------------------------------
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Alpha | 1.32 | - | v0.1.0
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## Overview
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This optional feature provides a secure mechanism to obtain metadata
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on the allocated blocks of a CSI VolumeSnapshot, or the changed blocks between two arbitrary pairs of CSI VolumeSnapshot objects of the same PersistentVolume.
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Snapshot metadata must be fetched directly with the
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[Kuberenets SnapshotMetadata gRPC service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api)
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from an [external-snapshot-metadata](./external-snapshot-metadata.md)
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sidecar configured by the CSI driver.
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This bypasses the Kubernetes API server for the most part: the API
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server is only used to fetch the Kubernetes objects needed for secure, authorized and mutually authenticated communication.
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> See [Kubernetes Enhancement Proposal 3314](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking)
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> for details of the Changed Block Tracking feature.

‎book/src/external-snapshot-metadata.md

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# CSI external-snapshot-metadata
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## Status and Releases
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**Git Repository:** [https://github.com/kubernetes-csi/external-snapshot-metadata](https://github.com/kubernetes-csi/external-snapshot-metadata)
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### Supported Versions
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Latest stable release | Branch | Min CSI Version | Max CSI Version | Container Image | [Min K8s Version](project-policies.md#minimum-version) | [Max K8s Version](project-policies.md#maximum-version) | [Recommended K8s Version](project-policies.md#recommended-version) |
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--|--|--|--|--|--|--|--
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v0.1.0 | [v0.1.0](https://github.com/kubernetes-csi/external-snapshot-metadata/releases/tag/v0.1.0) | [v1.10.0](https://github.com/container-storage-interface/spec/releases/tag/v1.10.0) | - | gcr.io/k8s-staging-sig-storage/csi-snapshot-metadata:v0.1.0 | v1.32 | - | v1.32
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## Alpha
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### Description
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The sidecar securely serves snapshot metadata to Kubernetes clients through the
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[Kubernetes SnapshotMetadata gRPC Service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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The sidecar authenticates and authorizes each Kubernetes backup application request made through the
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Kubernetes SnapshotMetadata gRPC Service API.
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It then acts as a proxy as it fetches the desired metadata from the CSI driver and
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streams it directly to the requesting application with no load on the Kubernetes API server.
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See ["The External Snapshot Metadata Sidecar"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-external-snapshot-metadata-sidecar)
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section in the CSI Changed Block Tracking KEP for additional details on the sidecar.
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### Usage
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Backup applications, identified by authorized ServiceAccount objects, directly communicate with the sidecar using the
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[Kubernetes SnapshotMetadata gRPC Service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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The authorization needed is described in the
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["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
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section of the CSI Changed Block Tracking KEP.
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The existence of this optional service is advertised by the presence of a
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[Snapshot Metadata Service CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource),
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named for the CSI driver that provisions the PersistentVolume and VolumeSnapshot objects involved.
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The CR contains the sidecar's address, CA certificate and audience string.
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The backup application must use the Kubernetes
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[TokenRequest](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-request-v1/)
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API with the sidecar's audience string to obtain a Kubernetes authentication token for use in the
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Kubernetes SnapshotMetadata gRPC Service API call.
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The backup application should establish trust for the sidecar CA certificate before making the API call
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to the specified address.
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The sidecar repository contains a
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[snapshot-metadata-lister](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/master/examples/snapshot-metadata-lister)
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example command to illustrate how a Kubernetes backup application can fetch snapshot metadata
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through the Kubernetes SnapshotMetadata gRPC Service API.
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It utilizes the services provided by the
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[pkg/iterator](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/master/pkg/iterator)
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Go package, which can be used by the backup application if desired.
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VolumeSnapshot metadata can be lengthy, and the Kubernetes SnapshotMetadata gRPC Service supports
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restarting an interrupted metadata request from an intermediate point in case of failure.
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### Deployment
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The CSI `external-snapshot-metadata` sidecar should be deployed by
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CSI drivers that support the
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[Changed Block Tracking](./changed-block-tracking.md) feature.
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The sidecar must be deployed in the same pod as the CSI driver and
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will communicate with its CSI [SnapshotMetadata](https://github.com/container-storage-interface/spec/blob/master/spec.md#snapshot-metadata-service-rpcs)
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and [Identity](https://github.com/container-storage-interface/spec/blob/master/spec.md#identity-service-rpc) gRPC services
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over a UNIX domain socket.
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The sidecar should be configured to run under the authority of its
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CSI driver ServiceAccount, which must be authorized as described
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in the
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["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
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section of the CSI Changed Block Tracking KEP.
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In particular, this requires the ability to
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use the Kubernetes
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[TokenReview](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-review-v1/)
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and
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[SubjectAccessReview](https://kubernetes.io/docs/reference/kubernetes-api/authorization-resources/subject-access-review-v1/)
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APIs.
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A Service object must be created for the TCP based [Kubernetes SnapshotMetadata](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api)
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gRPC service implemented by the sidecar.
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A [SnapshotMetadataService CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource),
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named for the CSI driver, must be created to advertise the
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availability of this optional feature.
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The CR contains the CA certificate and Service endpoint address
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of the sidecar and the audience string needed for the client
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authentication token.
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