Documentation on the external-snaphot-metadata sidecar (alpha).

book/src/SUMMARY.md

@@ -18,6 +18,7 @@
         - [cluster-driver-registrar](cluster-driver-registrar.md) (deprecated)
         - [external-health-monitor-controller](external-health-monitor-controller.md)
         - [external-health-monitor-agent](external-health-monitor-agent.md)
+        - [external-snapshot-metadata](external-snapshot-metadata.md)
     - [CSI objects](csi-objects.md)
       - [CSIDriver Object](csi-driver-object.md)
       - [CSINode Object](csi-node-object.md)
@@ -43,6 +44,7 @@
         - [CSI Windows](csi-windows.md)
         - [Volume Mode Conversion](prevent-volume-mode-conversion.md)
         - [Cross-Namespace Data Sources](cross-namespace-data-sources.md)
+        - [Changed Block Tracking](changed-block-tracking.md)
 - [Deploying a CSI Driver on Kubernetes](deploying.md)
     - [Example](example.md)
 - [Driver Testing](testing-drivers.md)

book/src/changed-block-tracking.md

@@ -0,0 +1,23 @@
+# Changed Block Tracking
+
+## Status
+
+Status | Min K8s Version | Max K8s Version | external-snapshot-metadata Version
+-------|-----------------|-----------------|-----------------------------------
+Alpha  | 1.32            | -               | v0.1.0
+
+
+## Overview
+
+This optional feature provides a secure mechanism to obtain metadata
+on the allocated blocks of a CSI VolumeSnapshot, or the changed blocks between two arbitrary pairs of CSI VolumeSnapshot objects of the same PersistentVolume.
+
+Snapshot metadata must be fetched directly with the
+[Kuberenets SnapshotMetadata gRPC service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api)
+from an [external-snapshot-metadata](./external-snapshot-metadata.md) 
+sidecar configured by the CSI driver.
+This bypasses the Kubernetes API server for the most part: the API
+server is only used to fetch the Kubernetes objects needed for secure, authorized and mutually authenticated communication.
+
+> See [Kubernetes Enhancement Proposal 3314](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking) 
+> for details of the Changed Block Tracking feature.

book/src/external-snapshot-metadata.md

@@ -0,0 +1,87 @@
+# CSI external-snapshot-metadata
+
+## Status and Releases
+
+**Git Repository:** [https://github.com/kubernetes-csi/external-snapshot-metadata](https://github.com/kubernetes-csi/external-snapshot-metadata)
+
+### Supported Versions
+
+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) |
+--|--|--|--|--|--|--|--
+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
+
+
+## Alpha
+
+### Description
+The sidecar securely serves snapshot metadata to Kubernetes clients through the
+[Kubernetes SnapshotMetadata gRPC Service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
+
+The sidecar authenticates and authorizes each Kubernetes backup application request made through the
+Kubernetes SnapshotMetadata gRPC Service API.
+It then acts as a proxy as it fetches the desired metadata from the CSI driver and
+streams it directly to the requesting application with no load on the Kubernetes API server.
+
+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)
+section in the CSI Changed Block Tracking KEP for additional details on the sidecar.
+
+### Usage
+Backup applications, identified by authorized ServiceAccount objects, directly communicate with the sidecar using the
+[Kubernetes SnapshotMetadata gRPC Service](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
+The authorization needed is described in the 
+["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
+section of the CSI Changed Block Tracking KEP.
+
+The existence of this optional service is advertised by the presence of a
+[Snapshot Metadata Service CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource),
+named for the CSI driver that provisions the PersistentVolume and VolumeSnapshot objects involved.
+The CR contains the sidecar's address, CA certificate and audience string.
+The backup application must use the Kubernetes 
+[TokenRequest](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-request-v1/)
+API with the sidecar's audience string to obtain a Kubernetes authentication token for use in the
+Kubernetes SnapshotMetadata gRPC Service API call.
+The backup application should establish trust for the sidecar CA certificate before making the API call
+to the specified address.
+
+The sidecar repository contains a
+[snapshot-metadata-lister](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/master/examples/snapshot-metadata-lister)
+example command to illustrate how a Kubernetes backup application can fetch snapshot metadata
+through the Kubernetes SnapshotMetadata gRPC Service API.
+It utilizes the services provided by the
+[pkg/iterator](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/master/pkg/iterator)
+Go package, which can be used by the backup application if desired.
+
+VolumeSnapshot metadata can be lengthy, and the Kubernetes SnapshotMetadata gRPC Service supports
+restarting an interrupted metadata request from an intermediate point in case of failure.
+
+### Deployment
+The CSI `external-snapshot-metadata` sidecar should be deployed by
+CSI drivers that support the
+[Changed Block Tracking](./changed-block-tracking.md) feature.
+The sidecar must be deployed in the same pod as the CSI driver and
+will communicate with its CSI [SnapshotMetadata](https://github.com/container-storage-interface/spec/blob/master/spec.md#snapshot-metadata-service-rpcs)
+and [Identity](https://github.com/container-storage-interface/spec/blob/master/spec.md#identity-service-rpc) gRPC services
+over a UNIX domain socket.
+
+The sidecar should be configured to run under the authority of its
+CSI driver ServiceAccount, which must be authorized as described
+in the 
+["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
+section of the CSI Changed Block Tracking KEP.
+In particular, this requires the ability to
+use the Kubernetes
+[TokenReview](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-review-v1/)
+and
+[SubjectAccessReview](https://kubernetes.io/docs/reference/kubernetes-api/authorization-resources/subject-access-review-v1/)
+APIs.
+
+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)
+gRPC service implemented by the sidecar.
+
+A [SnapshotMetadataService CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource),
+named for the CSI driver, must be created to advertise the
+availability of this optional feature.
+The CR contains the CA certificate and Service endpoint address
+of the sidecar and the audience string needed for the client
+authentication token.
+