What is the basis for forbidding volume multi-attach ?

[NickrenREN]

We expect the AccessModes in PV spec to be the all ways the volume supports,

kubernetes/pkg/apis/core/types.go

Lines 278 to 280 in 029bb4e

	// AccessModes contains all ways the volume can be mounted
	// +optional
	AccessModes []PersistentVolumeAccessMode

and AccessModes in PVC spec is what user wants.

kubernetes/pkg/apis/core/types.go

Lines 393 to 395 in 029bb4e

	// Contains the types of access modes required
	// +optional
	AccessModes []PersistentVolumeAccessMode

then which one should we take into account to forbid multi-attach ?
For example: RBD for now support RWO and ROX (we can create a PV with AccessModes setting to RWO and ROX), if a user create a PVC with RWO, should we forbid multi-attach ?

What happened:
Depending on AccessModes in PV spec. Will not forbid multi-attach in the situation described above.

What you expected to happen:
Depending on AccessModes in PVC spec (what user wants)

/assign
/sig storage
/cc @jsafrane @msau42 @jingxu97

[adampl]

@NickrenREN Did you test this on a multi-node cluster? Keep in mind that Access Modes work on node level, so multiple pods on the same node can access an RWO volume: https://kubernetes.io/docs/concepts/storage/persistent-volumes/#access-modes
I guess this is because volumes are mounted by nodes, not individual pods.

BTW, I don't understand why AccessModes in PVC is an array, because according to docs a PV can be mounted in only one access mode at the same time. I suspect it's an array because the volume provisioner copies this array to the PV spec, but IMHO it should rather create a single-item array from the single access mode defined in the PVC spec.

[fejta-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

[fejta-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle rotten

[fejta-bot]

Rotten issues close after 30d of inactivity.
Reopen the issue with /reopen.
Mark the issue as fresh with /remove-lifecycle rotten.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/close

[k8s-ci-robot]

@fejta-bot: Closing this issue.

In response to this:

Rotten issues close after 30d of inactivity.
Reopen the issue with /reopen.
Mark the issue as fresh with /remove-lifecycle rotten.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.