Merge pull request #32418 from bswartz/volume-populators-beta-blog

v1.24 blog post: Volume populators beta

Author: k8s-ci-robot

content/en/blog/_posts/2022-05-16-volume-populators-beta.md

@@ -0,0 +1,162 @@
+---
+layout: blog
+title: "Kubernetes 1.24: Volume Populators Graduate to Beta"
+date: 2022-05-16
+slug: volume-populators-beta
+---
+
+**Author:**
+Ben Swartzlander (NetApp)
+
+The volume populators feature is now two releases old and entering beta! The `AnyVolumeDataSouce` feature
+gate defaults to enabled in Kubernetes v1.24, which means that users can specify any custom resource
+as the data source of a PVC.
+
+An [earlier blog article](/blog/2021/08/30-volume-populators-redesigned/) detailed how the
+volume populators feature works. In short, a cluster administrator can install a CRD and
+associated populator controller in the cluster, and any user who can create instances of 
+the CR can create pre-populated volumes by taking advantage of the populator.
+
+Multiple populators can be installed side by side for different purposes. The SIG storage
+community is already seeing some implementations in public, and more prototypes should
+appear soon.
+
+Cluster administrations are **strongly encouraged** to install the
+volume-data-source-validator controller and associated `VolumePopulator` CRD before installing
+any populators so that users can get feedback about invalid PVC data sources.
+
+## New Features
+
+The [lib-volume-populator](https://github.com/kubernetes-csi/lib-volume-populator) library
+on which populators are built now includes metrics to help operators monitor and detect
+problems. This library is now beta and latest release is v1.0.1.
+
+The [volume data source validator](https://github.com/kubernetes-csi/volume-data-source-validator)
+controller also has metrics support added, and is in beta. The `VolumePopulator` CRD is
+beta and the latest release is v1.0.1.
+
+## Trying it out
+
+To see how this works, you can install the sample "hello" populator and try it
+out.
+
+First install the volume-data-source-validator controller.
+
+```shell
+kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/volume-data-source-validator/v1.0.1/client/config/crd/populator.storage.k8s.io_volumepopulators.yaml
+kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/volume-data-source-validator/v1.0.1/deploy/kubernetes/rbac-data-source-validator.yaml
+kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/volume-data-source-validator/v1.0.1/deploy/kubernetes/setup-data-source-validator.yaml
+```
+
+Next install the example populator.
+
+```shell
+kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/lib-volume-populator/v1.0.1/example/hello-populator/crd.yaml
+kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/lib-volume-populator/87a47467b86052819e9ad13d15036d65b9a32fbb/example/hello-populator/deploy.yaml
+```
+
+Your cluster now has a new CustomResourceDefinition that provides a test API named Hello.
+Create an instance of the `Hello` custom resource, with some text:
+
+```yaml
+apiVersion: hello.example.com/v1alpha1
+kind: Hello
+metadata:
+  name: example-hello
+spec:
+  fileName: example.txt
+  fileContents: Hello, world!
+```
+
+Create a PVC that refers to that CR as its data source.
+
+```yaml
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: example-pvc
+spec:
+  accessModes:
+  - ReadWriteOnce
+  resources:
+    requests:
+      storage: 10Mi
+  dataSourceRef:
+    apiGroup: hello.example.com
+    kind: Hello
+    name: example-hello
+  volumeMode: Filesystem
+```
+
+Next, run a Job that reads the file in the PVC.
+
+```yaml
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: example-job
+spec:
+  template:
+    spec:
+      containers:
+        - name: example-container
+          image: busybox:latest
+          command:
+            - cat
+            - /mnt/example.txt
+          volumeMounts:
+            - name: vol
+              mountPath: /mnt
+      restartPolicy: Never
+      volumes:
+        - name: vol
+          persistentVolumeClaim:
+            claimName: example-pvc
+```
+
+Wait for the job to complete (including all of its dependencies).
+
+```shell
+kubectl wait --for=condition=Complete job/example-job
+```
+
+And last examine the log from the job.
+
+```shell
+kubectl logs job/example-job
+```
+
+The output should be:
+
+```terminal
+Hello, world!
+```
+
+Note that the volume already contained a text file with the string contents from
+the CR. This is only the simplest example. Actual populators can set up the volume
+to contain arbitrary contents.
+
+## How to write your own volume populator
+
+Developers interested in writing new poplators are encouraged to use the
+[lib-volume-populator](https://github.com/kubernetes-csi/lib-volume-populator) library
+and to only supply a small controller wrapper around the library, and a pod image
+capable of attaching to volumes and writing the appropriate data to the volume.
+
+Individual populators can be extremely generic such that they work with every type
+of PVC, or they can do vendor specific things to rapidly fill a volume with data
+if the volume was provisioned by a specific CSI driver from the same vendor, for
+example, by communicating directly with the storage for that volume.
+
+## How can I learn more?
+
+The enhancement proposal,
+[Volume Populators](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/1495-volume-populators), includes lots of detail about the history and technical implementation
+of this feature.
+
+[Volume populators and data sources](/docs/concepts/storage/persistent-volumes/#volume-populators-and-data-sources), within the documentation topic about persistent volumes,
+explains how to use this feature in your cluster.
+
+Please get involved by joining the Kubernetes storage SIG to help us enhance this
+feature. There are a lot of good ideas already and we'd be thrilled to have more!
+