The CSI external-snapshotter is part of Kubernetes implementation of Container Storage Interface (CSI).
The volume snapshot feature supports CSI v1.0 and it has been an Alpha feature in Kubernetes since v1.12.
CSI Snapshotter is an external controller that watches Kubernetes Snapshot CRD objects and triggers CreateSnapshot/DeleteSnapshot against a CSI endpoint. Full design can be found at Kubernetes proposal at here
External snapshotter follows controller pattern and uses informers to watch for
VolumeSnapshotContent create/update/delete events. It filters out these objects with
Snapshotter==<CSI driver name> specified in the associated VolumeSnapshotClass object and then processes these events in workqueues with exponential backoff.
Snapshotter talks to CSI over socket (/run/csi/socket by default, configurable by -csi-address). The snapshotter then:
Discovers the supported snapshotter name by
Uses ControllerGetCapabilities for find out if CSI driver supports
ControllerServiceCapability_RPC_LIST_SNAPSHOTScalls. Otherwise, the controller will not start.
VolumeSnapshots: The snapshotter only processes
snapshotterspecified in its
VolumeSnapshotClassmatches its driver name. The process workflow is as follows
- If the snapshot status is
Ready, the controller checks whether the snapshot and its content still binds correctly. If there is any problem with the binding (e.g., snapshot points to a non-exist snapshot content), update the snapshot status and emit event.
- If the snapshot status is not ready, there are two cases.
SnapshotContentNameis not empty: the controller verifies whether the snapshot content exists and also binds to the snapshot. If verification passes, the controller binds the snapshot and its content objects and marks it is ready. Otherwise, it updates the error status of the snapshot.
SnapshotContentNameis set empty: the controller will first check whether there is already a content object which binds the snapshot correctly with snapshot uid (
VolumeSnapshotRef.UID) specified. If so, the controller binds these two objects. Otherwise, the controller issues a create snapshot operation. Please note that if the error status shows that snapshot creation already failed before, it will not try to create snapshot again.
- If the snapshot status is
VolumeSnapshotContents: The snapshotter only processes
VolumeSnapshotContentin which the CSI driver specified in the spec matches the controller's driver name.
- If the
VolumeSnapshotRefis set to nil, skip this content since it is not bound to any snapshot object.
- Otherwise, the controller verifies whether the content object is correctly bound to a snapshot object. In case the
VolumeSnapshotRef.UIDis set but it does not match its snapshot object or snapshot no long exists, the content object and its associated snapshot will be deleted.
- If the
Running on command line
For debugging, it is possible to run snapshotter on command line. For example,
$ csi-snapshotter -kubeconfig ~/.kube/config -v 5 -csi-address /run/csi/socket
Running in a statefulset
It is necessary to create a new service account and give it enough privileges to run the snapshotter. We provide .yaml files that deploy for use together with the hostpath example driver. A real production deployment must customize them:
$ for i in $(find deploy/kubernetes -name '*.yaml'); do kubectl create -f $i; done
Running Unit Tests:
$ go test -timeout 30s github.com/kubernetes-csi/external-snapshotter/pkg/controller
$ dep ensure
To modify dependencies or versions change
Community, discussion, contribution, and support
Learn how to engage with the Kubernetes community on the community page.
You can reach the maintainers of this project at:
Code of conduct
Participation in the Kubernetes community is governed by the Kubernetes Code of Conduct.