fix(nvca): derive the shared filesystem cache reader from the writer volume - #1434
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…volume doModelCacheSharedFS created its reader as a claim naming only the shared StorageClass, trusting the class to make every claim resolve to the same data. A dynamic provisioner does not: it answers each claim with a new volume. The reader therefore mounted an empty directory while binding cleanly, so nothing alerted, and the workload found no model. Measured on two clusters. On Weka the writer held csivol-pvc-8e38c07d and a fresh reader claim on the same StorageClass came back with csivol-pvc-e244d567, empty and writable. On OCI FSS the writer held export csi-fss-eaf964b0 and the reader got csi-fss-707da05a, containing only .snapshot. The reader is now a PV derived from the volume the writer populated, claimed by name with an empty StorageClass so no provisioner is involved, ReadOnlyMany and Retain so one namespace's reader can never destroy a cache others are reading. That is the shape NVMesh and Samba already used; sharedfs was the only backend relying on the class to share. deriveReaderVolumeHandle holds the only vendor specific step. NVMesh encodes the consuming namespace in its CSI volume handle and needs the reader namespace substituted in; Weka and OCI FSS address one volume by one handle and reuse the writer's unchanged. Both were measured: Weka handles are weka/v2/csivol-<id> and FSS handles are <filesystem-ocid>:<mount-target-ip>:<export-path>. Removes pkg/storage/cacheprobe. It existed to discover at run time, by creating a PVC and a Pod, whether the shared class supported ReadOnlyMany or ReadWriteMany. Deriving the reader from the writer volume removes the question. Also corrects a test fixture that gave an NVMesh PV the CSI driver "nvmesh"; the real name is nvmesh-csi.excelero.com, which is what the rest of the model cache code compares against the StorageClass provisioner. Relates to #1433 Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
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Included review availability: Your plan provides up to 12 included reviews per hour; 10 remain after this review. 📝 WalkthroughWalkthroughThe shared-FS model-cache reader now reuses the writer’s bound CSI volume through derived read-only PV and PVC resources. Driver-specific handle rewriting remains for NVMesh. Cache-probe implementation, tests, and Bazel dependencies were removed. ChangesModel cache reader provisioning
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🟡 Moderate · up to The PR changes shared-filesystem readers from independently provisioned claims to statically bound, read-only views of the writer volume, fixing empty-cache behavior. However, reconciliation can accept stale or conflicting reader storage objects without verifying the expected volume identity and read-only contract, which could expose the wrong cache data or weaken isolation; merge should wait for validation and fail-closed handling or explicit owner acceptance. Sequence Diagram(s)sequenceDiagram
participant ModelCacheController
participant KubernetesAPI
participant WriterPV
participant ReaderPV
participant ReaderPVC
ModelCacheController->>KubernetesAPI: Resolve bound writer PV
KubernetesAPI-->>ModelCacheController: Return writer CSI volume handle
ModelCacheController->>ReaderPV: Create retained read-only PV
ModelCacheController->>ReaderPVC: Create PVC bound to ReaderPV
ReaderPVC->>WriterPV: Reuse writer CSI volume
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Linked Issues checkExplanation The changes satisfy issue Full details: Docstring CoverageExplanation Docstring coverage is 77.78% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 2 files. (1 skipped: 1 unsupported.) Full details: Title checkExplanation The title follows Conventional Commits syntax with the required scoped
✨ Finishing Touches🧪 Generate unit tests (beta)
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In `@src/compute-plane-services/nvca/pkg/storage/modelcache.go`:
- Around line 1805-1812: Update newSharedFSReaderPV in
src/compute-plane-services/nvca/pkg/storage/modelcache.go:1805-1812 to clear
roPV.Spec.StorageClassName after deep-copying the writer PV. Add assert.Empty(t,
roPV.Spec.StorageClassName) in
src/compute-plane-services/nvca/pkg/storage/modelcache_test.go:1451-1452 to
verify the derived reader PV has no storage class.
Apply the same fix in
`@src/compute-plane-services/nvca/pkg/storage/modelcache_test.go` around lines
1451 - 1452: Add an assertion that the reader PV StorageClassName is empty.
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src/compute-plane-services/nvca/pkg/storage/BUILD.bazelsrc/compute-plane-services/nvca/pkg/storage/cacheprobe/BUILD.bazelsrc/compute-plane-services/nvca/pkg/storage/cacheprobe/cacheprobe_test.gosrc/compute-plane-services/nvca/pkg/storage/cacheprobe/configmap.gosrc/compute-plane-services/nvca/pkg/storage/cacheprobe/probe.gosrc/compute-plane-services/nvca/pkg/storage/modelcache.gosrc/compute-plane-services/nvca/pkg/storage/modelcache_test.go
💤 Files with no reviewable changes (5)
- src/compute-plane-services/nvca/pkg/storage/BUILD.bazel
- src/compute-plane-services/nvca/pkg/storage/cacheprobe/cacheprobe_test.go
- src/compute-plane-services/nvca/pkg/storage/cacheprobe/BUILD.bazel
- src/compute-plane-services/nvca/pkg/storage/cacheprobe/probe.go
- src/compute-plane-services/nvca/pkg/storage/cacheprobe/configmap.go
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The derived reader PV deep-copies the writer PV, so it inherited the writer's storage class, while the reader claim is built from scratch and asks for no class at all. Kubernetes validates that a pre-bound PV and claim agree on storage class, so the pair never binds and every reader claim stays Pending. The NVMesh path this replaces did not hit it because there the reader claim is a copy of the writer claim, so both sides carried the same class and matched by accident. Building the claim explicitly broke that coincidence. The reader PV is static and pre-bound by claimRef, so no provisioner is involved and it should carry no class. Clear it, which is also what the claim's own comment already said the design was. No unit test could catch this: nothing in the suite runs the PV binding controller. The added assertion compares the PV and claim against each other rather than checking either side alone, and fails without the fix. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
The derived reader inherited the writer's mount options through the deep copy, so it never went through resolveCacheMountOptions the way the NVMesh reader does. That function is not NVMesh specific: it maps a provisioner to the options its read-only attach requires, via the cache mount options ConfigMap. Harmless today, because only the shared filesystem backends reach this path and they need nothing special. It stops being harmless when the nvcf-sc-30 marker class goes away: NVMesh is then identified by provisioner like every other backend and resolves to the shared filesystem flow, where its reader attaches the same XFS filesystem as the writer and needs nouuid and norecovery or the mount fails outright. Inheriting the writer's read-write options is the wrong answer there twice over. deriveReaderVolumeHandle in this same function already rewrites the handle for the NVMesh driver, so the path was already built for NVMesh reaching it. This finishes that. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
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Inline comments:
In `@src/compute-plane-services/nvca/pkg/storage/modelcache.go`:
- Line 1841: In the derived PV construction around writerPV.DeepCopy, set
roPV.Spec.CSI.ReadOnly to true after rewriting the volume handle, before
resolving mount options, so all consumers receive a read-only CSI source. Add or
update an assertion covering this value.
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The reader inherited the writer's read-write CSI source through the deep copy. Access modes do not close that gap: the kubelet uses them for binding and does not enforce them at mount time. That leaves mount options as the only protection, and they are empty for a provisioner that declares none. NVMesh happens to be safe because its reader options carry ro, but a shared filesystem such as Weka or OCI FSS gets nothing, and those are precisely the backends where one volume is shared across namespaces. A consumer could mount the cache read-write and corrupt it for every other reader. Setting the CSI source read-only makes the reader read-only regardless of what a provisioner declares. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
The SDD said a sharedfs reader is a claim on the shared class and that the class shares data across namespaces. That is the assumption this change removes, so the document now describes the derived reader PV and closes the corresponding known gap. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
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… cache SDD" This reverts commit 9cef0f6. The model cache design now lives in one document on the catalog change, so this branch must not edit the file that change removes. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
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3 participants
Why
doModelCacheSharedFScreated each namespace's reader as a claim naming onlythe shared StorageClass, trusting the class to make every claim resolve to the
same data. A dynamic provisioner answers each claim with a new volume, so the
reader mounted an empty directory. The claim binds, the pod starts, the mount
succeeds, and the workload finds no model. Nothing alerts.
Measured on two clusters. On Weka the writer held
csivol-pvc-8e38c07d; afresh reader claim on the same StorageClass came back with
csivol-pvc-e244d567, empty and writable. On OCI FSS the writer held exportcsi-fss-eaf964b0and the reader gotcsi-fss-707da05a, containing only.snapshot.What changed
The reader is a PV derived from the volume the writer populated, claimed by
name with an empty StorageClass so no provisioner is involved,
ReadOnlyManyand
Retainso one namespace's reader cannot destroy a cache others arereading. That is the shape NVMesh and Samba already used; sharedfs was the only
backend relying on the class to share.
Three properties of the derived PV are set deliberately rather than inherited
from the writer through the deep copy, and each was a bug until it was:
storageClassNameis cleared, because Kubernetes refuses to bind a pre-bound PVand claim whose classes differ;
csi.readOnlyis true, because access modes arenot enforced at mount time and a reader with the writer's read-write source
could corrupt the cache for every other namespace; and
mountOptionsareresolved per provisioner, because NVMesh readers need
nouuidandnorecoveryor the mount fails outright.
deriveReaderVolumeHandleholds the only vendor specific step. NVMesh encodesthe consuming namespace in its CSI volume handle and needs the reader namespace
substituted in. Weka and OCI FSS address one volume by one handle and reuse the
writer's unchanged.
Removes
pkg/storage/cacheprobe: it existed to discover at run time, bycreating a PVC and a Pod, whether the shared class supported ROX or RWX.
Deriving the reader from the writer volume removes the question. Net 252 added,
831 removed.
Customer Release Notes
Fixed Helm model caching silently serving an empty cache on shared filesystem
storage classes that provision a volume per claim, which includes Weka and OCI
FSS.
Plan Summary
Not applicable.
Usage
No operator action. The reader is derived automatically; a cache populated
before this change keeps working, because readers are derived from whatever
volume the writer claim is bound to.
Testing
TestReconcile_ModelCacheSharedFSnow binds the writer claim to a real volumeand asserts the reader PV addresses it, that the reader claim binds by name,
and that the PV and claim agree on StorageClass. It fails against the old code.
TestNewSharedFSReaderPVResolvesMountOptionsandTestNewSharedFSReaderPVIsReadOnlyWithoutMountOptionspin the mount optionsand the read-only CSI source, including the case of a provisioner that declares
no reader options. Each fails with its fix reverted.
TestDeriveReaderVolumeHandlecovers NVMesh rewriting, Weka and FSS reusingverbatim, an unknown driver, and a malformed NVMesh handle.
go build ./...,go test ./pkg/... ./internal/...andgofmtare clean.QA: worth a cluster run on a shared filesystem backend before release. The
storage behaviour is measured, but this build has not been deployed.
Notes
Split out of the storage-agnostic cache work so it can land on its own: it
fixes a defect that exists today and does not depend on the capability catalog.
Issues
Closes #1433
Related Pull Requests
Dependencies
None
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