An external dynamic provisioner for Kubernetes local persistent volumes.
The local volume driver, which went stable in Kubernetes 1.14, represents
a mounted local storage device. It is meant to be used with PersistedVolumes,
and requires the volume to have a node affinity. This project provisions
such volumes dynamically.
This project uses the sig-storage-lib-external-provisioner library. It implements the Provisioner interface defined in that library, and uses the supplied ProvisionController.
Like any other external provisioner, the project is an executable that runs in a container provisioned by Kubernetes. It takes two configuration parameters: nodename, which is the name of the Kubernetes node where it is scheduled, and rootpath, which is a directory on that node. The project creates subdirectories under its rootpath, and exposes these to Kubernetes as PersistentVolume objects. It attaches a nodeAffinity to these volumes, using the nodename.
The parameters are passed via environment variables called KUTTI_NODE_NAME and KUTTI_ROOT_PATH respectively. These are set via a Kubernetes manifest while deploying this provisioner.
The provisioner adds some annotations to the PersistentVolume objects that it creates. An instance of the provisioner on a node will only delete a PersistentVolume that was created by the provisioner on the same node. So, if the provisioner somehow gets rescheduled on a different node, any PersistentVolume objects created on the original node will not be deleted dynamically. They will continue to work as normal, and may be manually deleted as per the normal rules.
The reference implementation is published on the Docker Hub and Quay.io, as an image called kuttiproject/provisioner-localvolume:. The corresponding Kubernetes manifest file can be found in this repository, at deploy/kubernetes/provisioner.yaml.
The manifest file includes a ClusterRole and a corresponding ClusterRoleBinding. This is because the sig-storage-lib-external-provisioner library needs update permissions on EndPoint objects.
It uses a Deployment object to deploy the provisioner. The Deployment object
passes the hostname of the deployed node via the environment variable
KUTTI_NODE_NAME (using valueFrom). It also uses the hostpath driver to
mount a directory of the node into the container, and passes the path to
that directory via the environment variable KUTTI_ROOT_PATH.
Finally, it includes two StorageClass objects, with volumeReclaimPolicies of Delete and Retain, and marks the first one as default.