The standalone-cinder external provisioner fulfills persistent volume claims by creating cinder volumes and mapping them to natively supported volume sources. This approach allows cinder to be used as a storage service whether or not the cluster is deployed on Openstack. By mapping cinder volume connection information to native volume sources, persistent volumes can be attached and mounted using the standard kubelet machinery and without help from cinder.
The provisioner works by mapping cinder volume connections (iscsi, rbd, fc, etc) to the corresponding native/raw kubernetes volume types. New cinder types can be supported in the provisioner by creating a new implementation of the volumeMapper interface. The implementation is responsible for building a PersistentVolumeSource from cinder connection information and for setup and teardown of any authentication (CHAP secret, cephx secret, etc) if required.
Support for cinder backends without a corresponding kubernetes raw volume implementation could be added in the future by providing a FlexVolume implementation for the type.
The provisioner directly uses the gophercloud SDK to connect to cinder (as opposed to use of the cloudprovider interface). The intention is to support two modes of operation: a conventional cinder deployment with keystone managing authentication and providing the service catalog, and a standalone configuration where cinder is accessed directly.
Conventional cinder deployments can be used by supplying a cloud config file identical to the one you would use to configure an openstack cloud provider.
| User | Kubernetes | Provisioner | Cinder |
|---|---|---|---|
| Provision storage | |||
| Issue a PVC for a 100GB RWO volume | |||
| Posted the PVC on API server | |||
| Acquire the PVC and call cinder create | |||
| Create 100GB volume and return info | |||
| Call cinder reserve | |||
| Volume is marked as reserved/attaching | |||
| Call cinder os-initialize_connection | |||
| Create connection on storage server and return info (ISCSI target and LUN info) | |||
| Create PV using ISCSI as raw volume type using connection info | |||
| Bind the PV to the PVC | |||
| Use storage | |||
| Create a Pod including the PVC | |||
| Attach ISCSI PV to node | |||
| Create filesystem on device and mount into Pod | |||
| Pod is running | |||
| Delete Pod | |||
| Pod is stopped | |||
| Unmount filesystem | |||
| Detach ISCSI PV | |||
| Delete storage | |||
| Delete PVC | |||
| Call cinder os-terminate_connection | |||
| Remove connection on storage server | |||
| Call cinder unreserve | |||
| Volume is marked as available | |||
| Call cinder delete | |||
| Delete volume from storage | |||
| Delete PV |
Standalone cinder has support for provisioning new volumes as a clone of an existing PVC. To request a clone, the user should add a clone request annotation to the PVC:
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: clone-claim
annotations:
k8s.io/CloneRequest: default/source-pvc
The provisioner will locate the indicated PVC and determine the underlying associated cinder volume ID. The provisioner will use this ID as the source-vol-id parameter when provisioning the new volume resulting in a clone at the storage level.
Cloning will only work if the cinder backend supports "smart-cloning". This means that the clone will complete without the need for cinder to perform a bit-for-bit copy using the host. Because of this, the cinder provisioner will not attempt to clone unless the associated storage class contains the parameter: "smartclone" to indicate that volumes provisioned from this storage class can be cloned correctly.
If the provisioner was able to clone the volume it will apply the 'k8s.io/CloneOf' annotation to the PVC.