KEP-5489: Enable defining a default StorageClass for each specific volume access mode #5492

savirg · 2025-08-22T05:28:04Z

One-line PR description: Enable defining a default StorageClass for each specific volume access mode

Issue link: Enable defining a default StorageClass for each specific volume access mode #5489

Other comments:

k8s-ci-robot · 2025-08-22T05:28:13Z

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k8s-ci-robot · 2025-08-22T05:28:14Z

Hi @savirg. Thanks for your PR.

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msau42 · 2025-08-22T18:18:27Z

/ok-to-test

msau42 · 2025-08-22T18:18:39Z

/assign

msau42 · 2025-08-23T00:06:24Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+- Feature implemented behind a feature flag
+- Initial e2e tests completed and enabled
+
+#### Beta


Have the beta and GA sections been filled out?

Do I need to fill them now or after the alpha release?

It would be good to fill it out now. If it needs further adjustments in later releases, we can still change them.

msau42 · 2025-08-23T00:08:01Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+-->
+
+- [ ] Feature gate (also fill in values in `kep.yaml`)
+  - Feature gate name:


Fill these out

msau42 · 2025-08-23T00:11:02Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+not need to be as detailed as the proposal, but should include enough
+information to express the idea and why it was not acceptable.
+-->
+


Here I would mention the other alternatives discussed in this issue: kubernetes/kubernetes#89911

The main challenges with the webhook or mutating admission policy approaches is the ordering with the builtin defaultstorageclass admission controller. We would have to migrate the existing admission controller to solve the ordering problems, and that still wouldn't address the logic in the PV controller.

keps/sig-storage/5489-default-storage-class-per-access-mode/kep.yaml

…s mode

k8s-ci-robot · 2025-08-25T07:38:41Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: savirg
Once this PR has been reviewed and has the lgtm label, please ask for approval from msau42. For more information see the Code Review Process.

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sunnylovestiramisu · 2025-09-08T17:10:52Z

keps/sig-storage/5489-default-storage-class-per-access-mode/kep.yaml

+
+# The milestone at which this feature was, or is targeted to be, at each stage.
+milestone:
+  alpha: "v1.35"


Should this be beta? Or we still go through 3 release cycles?

alpha, beta, GA is the typical cycle

msau42 · 2025-09-09T16:56:48Z

/retest

k8s-ci-robot · 2025-09-09T17:00:14Z

@savirg: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-enhancements-test	`938eecc`	link	true	`/test pull-enhancements-test`
pull-enhancements-verify	`938eecc`	link	true	`/test pull-enhancements-verify`

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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msau42 · 2025-09-09T19:22:22Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+If e2e tests are not necessary or useful, explain why.
+-->
+
+For the **Alpha** release, a focused suite of end-to-end (e2e) tests will be added to `test/e2e/storage`. These tests are designed to validate the complete user journey, from `PersistentVolumeClaim` (PVC) creation to successful `PersistentVolume` (PV) provisioning and binding, ensuring the feature works correctly in a fully functional cluster.


The challenge with e2e tests is different environments won't have the supported storage providers to test the full provisioning path. And changing the default storageclasses may not be allowed in some environments. I think for e2e tests, we need to leave it to the cluster provider to install appropriate storageclasses, and in the tests, if the default storageclasses are set, then we trigger the tests.

msau42 · 2025-09-09T19:24:17Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+- Feature implemented behind a feature flag
+- Initial e2e tests completed and enabled
+
+#### Beta


It would be good to fill it out now. If it needs further adjustments in later releases, we can still change them.

msau42 · 2025-09-09T19:29:45Z

keps/sig-storage/5489-default-storage-class-per-access-mode/README.md

+
+#### Kubernetes Mutating Admission Policies (CEL)
+
+This approach would leverage the built-in `MutatingAdmissionPolicy` feature, which uses the Common Expression Language (CEL) to define policies that can modify objects during admission. An administrator would create a `MutatingAdmissionPolicy` resource that inspects the `accessModes` of an incoming PVC and mutates the `storageClassName` field if it is empty.


This approach is actually a bit more complex. In order to choose which storageClassName to set, we typically have to iterate over all StorageClasses to find the ones with the right annotations and also consider all the priority rules that you outlined earlier. CEL cannot do this kind of logic, so we would need to implement a controller that evaluates the PVC and the StorageClasses, and then associate a ConfigMap to the PVC with the final result.

k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Aug 22, 2025

k8s-ci-robot requested a review from saad-ali August 22, 2025 05:28

k8s-ci-robot added the kind/kep Categorizes KEP tracking issues and PRs modifying the KEP directory label Aug 22, 2025

k8s-ci-robot requested a review from xing-yang August 22, 2025 05:28

k8s-ci-robot added the sig/storage Categorizes an issue or PR as relevant to SIG Storage. label Aug 22, 2025

k8s-ci-robot added the needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. label Aug 22, 2025

k8s-ci-robot added the size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. label Aug 22, 2025

savirg force-pushed the default-sc-for-mode branch 2 times, most recently from 427bfa3 to d326612 Compare August 22, 2025 05:42

k8s-ci-robot added size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. and removed size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. labels Aug 22, 2025

k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Aug 22, 2025

k8s-ci-robot assigned msau42 Aug 22, 2025

msau42 reviewed Aug 23, 2025

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Enable defining a default StorageClass for each specific volume acces…

938eecc

…s mode

savirg force-pushed the default-sc-for-mode branch from d326612 to 938eecc Compare August 25, 2025 07:38

sunnylovestiramisu reviewed Sep 8, 2025

View reviewed changes

msau42 reviewed Sep 9, 2025

View reviewed changes


		#### Kubernetes Mutating Admission Policies (CEL)

		This approach would leverage the built-in `MutatingAdmissionPolicy` feature, which uses the Common Expression Language (CEL) to define policies that can modify objects during admission. An administrator would create a `MutatingAdmissionPolicy` resource that inspects the `accessModes` of an incoming PVC and mutates the `storageClassName` field if it is empty.

KEP-5489: Enable defining a default StorageClass for each specific volume access mode #5492

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KEP-5489: Enable defining a default StorageClass for each specific volume access mode #5492

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savirg commented Aug 22, 2025

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k8s-ci-robot commented Aug 25, 2025

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msau42 commented Sep 9, 2025

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