Kubernetes Changed Block Tracking API - Beta Differences

The Kubernetes Changed Block Tracking (CBT) API has transitioned from Alpha to Beta, marking a step toward production readiness. The core change is the promotion of the SnapshotMetadataService Custom Resource Definition (CRD) from v1alpha1 to v1beta1. This version bump is breaking: v1alpha1 is no longer served, so Alpha users must manually reapply the CRD and update all manifests and client code to reference the new apiVersion. The schema itself remains unchanged, but the lack of automatic conversion means downtime or dual-version support is not an option during migration.

CBT targets block volumes exclusively, leaving file-based and network-attached storage out of scope. The feature relies on three components: a CSI SnapshotMetadata gRPC service, the SnapshotMetadataService CRD, and the external-snapshot-metadata sidecar. For a CSI driver to support CBT, it must already implement volume snapshots and bundle the sidecar. The Beta release does not expand the feature set but stabilizes the existing API for broader testing. Minimum requirements include Kubernetes 1.33, CSI spec 1.10, and the v1.0.0 sidecar image.

The Beta cycle prioritizes two goals: wider CSI driver adoption and operational feedback. Driver maintainers are encouraged to evaluate CBT support, while backup application developers can provide input on the streaming clients and iterator package. The external-snapshot-metadata repository, KEP-3314, and example clients like snapshot-metadata-lister serve as primary resources. No new functionality is introduced in this release, so the focus remains on hardening the existing implementation before a future GA release.