Add csi nodeexpandsecret blog article

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>
kubernetes · Sep 6, 2022 · 37b77be · 37b77be
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+---
+layout: blog
+title: >-
+  Kubernetes 1.25: Use Secrets for Node-Driven Expansion of CSI Volumes
+date: 2022-09-21
+slug: kubernetes-1-25-use-secrets-while-expanding-csi-volumes-on-node-alpha
+---
+
+**Author:** Humble Chirammal (Red Hat), Louis Koo (deeproute.ai)
+
+Kubernetes v1.25, released earlier this month, introduced a new feature
+that lets your cluster expand storage volumes, even when access to those
+volumes requires a secret (for example: a credential for accessing a SAN fabric)
+to perform node expand operation. This new behavior is in alpha and you
+must enable a feature gate (`CSINodeExpandSecret`) to make use of it.
+You must also be using [CSI](https://kubernetes-csi.github.io/docs/)
+storage; this change isn't relevant to storage drivers that are built in to Kubernetes.
+
+To turn on this new, alpha feature, you enable the `CSINodeExpandSecret` feature
+gate for the kube-apiserver and kubelet, which turns on a mechanism to send `secretRef`
+configuration as part of NodeExpansion  by the CSI drivers thus make use of
+the same to perform node side expansion operation with the underlying
+storage system.
+
+## What is this all about?
+
+Before Kubernetes v1.24, you were able to define a cluster-level StorageClass
+that made use of [StorageClass Secrets](https://kubernetes-csi.github.io/docs/secrets-and-credentials-storage-class.html),
+but you didn't have any mechanism to specify the credentials that would be used for
+operations that take place when the storage was mounted onto a node and when
+the volume has to be expanded at node side.
+
+The Kubernetes CSI already implemented a similar mechanism specific kinds of
+volume resizes; namely, resizes of PersistentVolumes where the resizes take place
+independently from any node referred as Controller Expansion. In that case, you
+associate a PersistentVolume with a Secret that contains credentials for volume resize
+actions, so that controller expansion can take place. CSI also supports a `nodeExpandVolume`
+operation which CSI drivers can make use independent of Controller Expansion or along with
+Controller Expansion on which, where the resize is driven from a node in your cluster where
+the volume is attached. Please read [Kubernetes 1.24: Volume Expansion Now A Stable Feature](/blog/2022/05/05/volume-expansion-ga/)
+
+- At times, the CSI driver needs to check the actual size of the backend block storage (or image)
+  before proceeding with a node-level filesystem expand operation. This avoids false positive returns
+  from the backend storage cluster during filesystem expands.
+
+- When a PersistentVolume represents encrypted block storage (for example using LUKS)
+  you need to provide a passphrase in order to expand the device, and also to make it possible
+  to grow the filesystem on that device.
+
+- For various validations at time of node expansion, the CSI driver has to be connected
+  to the backend storage cluster. If the `nodeExpandVolume` request includes a `secretRef`
+  then the CSI driver can make use of the same and connect to the storage cluster to
+  perform the cluster operations.
+
+## How does it work?
+
+To enable this functionality from this version of Kubernetes, SIG Storage have introduced
+a new feature gate called `CSINodeExpandSecret`. Once the feature gate is enabled
+in the cluster, NodeExpandVolume requests can include a `secretRef` field. The NodeExpandVolume request
+is part of CSI; for example, in a request which has been sent from the Kubernetes
+control plane to the CSI driver.
+
+As a cluster operator, you admin can specify these secrets as an opaque parameter in a StorageClass,
+the same way that you can already specify other CSI secret data. The StorageClass needs to have some
+CSI-specific parameters set. Here's an example of those parameters:
+
+```
+csi.storage.k8s.io/node-expand-secret-name: test-secret
+csi.storage.k8s.io/node-expand-secret-namespace: default
+```
+
+If feature gates are enabled and storage class carries the above secret configuration,
+the CSI provisioner receives the credentials from the Secret as part of the NodeExpansion request.
+
+CSI volumes that require secrets for online expansion will have NodeExpandSecretRef
+field set. If not set, the NodeExpandVolume CSI RPC call will be made without a secret.
+
+
+
+## Trying it out
+
+1. Enable the `CSINodeExpandSecret` feature gate (please refer to
+   [Feature Gates](https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/)).
+
+1. Create a Secret, and then a StorageClass that uses that Secret.
+
+Here's an example manifest for a Secret that holds credentials:
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: test-secret
+  namespace: default
+data:
+stringData:
+  username: admin
+  password: t0p-Secret
+```
+
+Here's an example manifest for a StorageClass that refers to those credentials:
+
+```yaml
+apiVersion: storage.k8s.io/v1
+kind: StorageClass
+metadata:
+  name: csi-blockstorage-sc
+parameters:
+  csi.storage.k8s.io/node-expand-secret-name: test-secret   # the name of the Secret
+  csi.storage.k8s.io/node-expand-secret-namespace: default  # the namespace that the Secret is in
+provisioner: blockstorage.cloudprovider.example
+reclaimPolicy: Delete
+volumeBindingMode: Immediate
+allowVolumeExpansion: true
+```
+
+
+## Example output
+
+If the PersistentVolumeClaim (PVC) was created successfully, you can see that
+configuration within the `spec.csi` field of the PersistentVolume (look for
+`spec.csi.nodeExpandSecretRef`).
+Check that it worked by running `kubectl get persistentvolume <pv_name> -o yaml`.
+You should see something like.
+
+```yaml
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  annotations:
+    pv.kubernetes.io/provisioned-by: blockstorage.cloudprovider.example
+  creationTimestamp: "2022-08-26T15:14:07Z"
+  finalizers:
+  - kubernetes.io/pv-protection
+  name: pvc-95eb531a-d675-49f6-940b-9bc3fde83eb0
+  resourceVersion: "420263"
+  uid: 6fa824d7-8a06-4e0c-b722-d3f897dcbd65
+spec:
+  accessModes:
+  - ReadWriteOnce
+  capacity:
+    storage: 6Gi
+  claimRef:
+    apiVersion: v1
+    kind: PersistentVolumeClaim
+    name: csi-pvc
+    namespace: default
+    resourceVersion: "419862"
+    uid: 95eb531a-d675-49f6-940b-9bc3fde83eb0
+  csi:
+    driver: blockstorage.cloudprovider.example
+    nodeExpandSecretRef:
+      name: test-secret
+      namespace: default
+    volumeAttributes:
+      storage.kubernetes.io/csiProvisionerIdentity: 1648042783218-8081-blockstorage.cloudprovider.example
+    volumeHandle: e21c7809-aabb-11ec-917a-2e2e254eb4cf
+  nodeAffinity:
+    required:
+      nodeSelectorTerms:
+      - matchExpressions:
+        - key: topology.hostpath.csi/node
+          operator: In
+          values:
+          - racknode01
+  persistentVolumeReclaimPolicy: Delete
+  storageClassName: csi-blockstorage-sc
+  volumeMode: Filesystem
+status:
+  phase: Bound
+```
+
+If you then trigger online storage expansion, the kubelet passes the appropriate credentials
+to the CSI driver, by loading that Secret and passing the data to the storage driver.
+
+Here's an example debug log:
+
+```console
+I0330 03:29:51.966241       1 server.go:101] GRPC call: /csi.v1.Node/NodeExpandVolume
+I0330 03:29:51.966261       1 server.go:105] GRPC request: {"capacity_range":{"required_bytes":7516192768},"secrets":"***stripped***","staging_target_path":"/var/lib/kubelet/plugins/kubernetes.io/csi/blockstorage.cloudprovider.example/f7c62e6e08ce21e9b2a95c841df315ed4c25a15e91d8fcaf20e1c2305e5300ab/globalmount","volume_capability":{"AccessType":{"Mount":{}},"access_mode":{"mode":7}},"volume_id":"e21c7809-aabb-11ec-917a-2e2e254eb4cf","volume_path":"/var/lib/kubelet/pods/bcb1b2c4-5793-425c-acf1-47163a81b4d7/volumes/kubernetes.io~csi/pvc-95eb531a-d675-49f6-940b-9bc3fde83eb0/mount"}
+I0330 03:29:51.966360       1 nodeserver.go:459] req:volume_id:"e21c7809-aabb-11ec-917a-2e2e254eb4cf" volume_path:"/var/lib/kubelet/pods/bcb1b2c4-5793-425c-acf1-47163a81b4d7/volumes/kubernetes.io~csi/pvc-95eb531a-d675-49f6-940b-9bc3fde83eb0/mount" capacity_range:<required_bytes:7516192768 > staging_target_path:"/var/lib/kubelet/plugins/kubernetes.io/csi/blockstorage.cloudprovider.example/f7c62e6e08ce21e9b2a95c841df315ed4c25a15e91d8fcaf20e1c2305e5300ab/globalmount" volume_capability:<mount:<> access_mode:<mode:SINGLE_NODE_MULTI_WRITER > > secrets:<key:"XXXXXX" value:"XXXXX" > secrets:<key:"XXXXX" value:"XXXXXX" >
+```
+
+## The future
+
+As this feature is still in alpha, Kubernetes Storage SIG expect to update or get feedback from CSI driver
+authors with more tests and implementation. The community plans to eventually
+promote the feature to Beta in upcoming releases.
+
+## Get involved or learn more?
+
+The enhancement proposal includes lots of detail about the history and technical
+implementation of this feature.
+
+To learn more about StorageClass based dynamic provisioning in Kubernetes, please refer to
+[Storage Classes](/docs/concepts/storage/storage-classes/) and
+[Persistent Volumes](/docs/concepts/storage/persistent-volumes/).
+
+Please get involved by joining the Kubernetes
+[Storage SIG](https://github.com/kubernetes/community/blob/master/sig-storage/README.md)
+(Special Interest Group) to help us enhance this feature.
+There are a lot of good ideas already and we'd be thrilled to have more!