Problem Being Solved
What this service provides
The CSI Hostpath Driver solves a common challenge for developers working with Kubernetes storage: how do you test and validate Container Storage Interface (CSI) workflows without setting up complex, production-grade storage infrastructure? This page explains the problem the driver addresses, the gap it fills in the Kubernetes ecosystem, and why it exists as a dedicated tool for development and evaluation workflows.
The challenge of testing CSI-based storage
The Container Storage Interface (CSI) is the standard API that allows Kubernetes to communicate with external storage systems. When you're building applications that depend on persistent storage, or when you're evaluating how CSI drivers behave in your cluster, you typically need a real storage backend — a network file system, a cloud block device, or a SAN. Setting up that infrastructure just to verify a workflow or prototype an application is expensive, time-consuming, and overkill for development purposes.
What the CSI Hostpath Driver provides
The CSI Hostpath Driver provides a minimal, self-contained CSI implementation that provisions volumes using the local filesystem of the Kubernetes node itself. Volumes are created as directories under /tmp inside the hostpath plugin container. This means:
- No external storage required. You can exercise the full CSI API surface — provisioning, attaching, mounting, snapshotting — without any backing storage system.
- Fast setup. A single deployment script brings up the driver along with its companion components (provisioner, attacher, snapshotter, and liveness probe sidecar).
- Real Kubernetes objects. The driver creates genuine
PersistentVolume,PersistentVolumeClaim,VolumeAttachment, andVolumeSnapshotobjects, so your application manifests and storage workflows behave exactly as they would against a production driver.
What the driver is not
Because volumes are stored on the node's local filesystem, they exist only as long as the driver's DaemonSet pod is running. Data does not survive pod restarts, and volumes are not replicated or made highly available. The CSI Hostpath Driver is intentionally scoped to testing and evaluation — it gives you a realistic CSI environment with none of the operational complexity, at the cost of durability and portability you would expect from a production storage system.
The workflow it enables
With the Hostpath Driver deployed, you can walk through the complete lifecycle of a CSI-backed application:
- Deploy the driver using the provided deployment script for your Kubernetes version.
- Provision a volume by creating a
StorageClass, aPVC, and a pod that mounts it — the same manifests you would write for any CSI driver. - Verify the driver by writing a file inside your application pod and confirming it appears in the hostpath container's
/tmpdirectory, or by inspecting theVolumeAttachmentobject that Kubernetes creates when the volume is attached. - Snapshot and restore volumes using the CSI snapshot API (requires the
VolumeSnapshotDataSourcefeature gate on Kubernetes 1.12+).
This end-to-end loop — deploy, provision, verify, snapshot — mirrors exactly what you would do with any production CSI driver, making the Hostpath Driver a reliable stand-in for early-stage development and CI environments.
Verifying a provisioned volume exists
After deploying the driver and creating the example application, confirm that Kubernetes has bound the PersistentVolumeClaim:
$ kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
csi-pvc Bound pvc-58d5ec38-03e5-11e9-be51-000c29e88ff1 1Gi RWO csi-hostpath-sc 93s
A STATUS of Bound confirms the driver received the provisioning request through the CSI API and created a backing volume.
Confirming data written through the CSI volume is visible on the host
Write a file inside the application pod through its mounted CSI volume:
$ kubectl exec -it my-csi-app /bin/sh
/ # touch /data/hello-world
/ # exit
Then locate the same file inside the hostpath plugin container to verify the volume is backed by the node's local filesystem:
$ kubectl exec -it $(kubectl get pods --selector app=csi-hostpathplugin \
-o jsonpath='{.items[*].metadata.name}') -c hostpath /bin/sh
/ # find / -name hello-world
/tmp/057485ab-c714-11e8-bb16-000c2967769a/hello-world
The file appearing under /tmp/<volume-id>/hello-world confirms that writes from your application are reaching the hostpath volume, and that the full CSI mount path is functioning correctly.
Inspecting the VolumeAttachment object
Kubernetes creates a VolumeAttachment object when a CSI volume is attached to a node. Inspecting it confirms the driver's attach workflow completed successfully:
$ kubectl describe volumeattachment
Name: csi-a7515d53b30a1193fd70b822b18181cff1d16422fd922692bce5ea234cb191e9
Spec:
Attacher: csi-hostpath
Node Name: 127.0.0.1
Source:
Persistent Volume Name: pvc-58d5ec38-03e5-11e9-be51-000c29e88ff1
Status:
Attached: true
Attached: true in the Status block means the CSI ControllerPublishVolume call succeeded and the volume is live on the node.
- Container Storage Interface (CSI) specification — The vendor-neutral API standard that the Hostpath Driver implements. Understanding CSI helps you interpret the objects (PV, PVC, VolumeAttachment, VolumeSnapshot) the driver creates.
- Kubernetes PersistentVolumes and PersistentVolumeClaims — The Kubernetes storage abstractions that sit above the CSI layer. Your applications interact with PVCs; the driver fulfills them.
- StorageClasses — The Kubernetes object that maps a PVC request to a specific CSI driver and its configuration. The Hostpath Driver registers itself as the provisioner for the
csi-hostpath-scStorageClass. - VolumeSnapshot API — The Kubernetes alpha API (available from v1.12 with the
VolumeSnapshotDataSourcefeature gate) that the Hostpath Driver supports for snapshot and restore workflows. - CSI liveness probe sidecar — A community-maintained container deployed alongside the driver that exposes health checks for the CSI gRPC services, relevant if you are monitoring driver availability.