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feat: add support for generic ephemeral volumes
Add a new feature flag `kubernetes.podspec-volumes-ephemeral` to allow generic ephemeral volumes (volumeClaimTemplate) in Knative services. This enables workloads that need per-pod dynamically provisioned storage, such as local NVMe scratch space on cloud VMs. Also exempt ephemeral volumes from the forced readOnly default, matching the existing behavior for emptyDir and PersistentVolumeClaim volumes. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
1 parent fb213e0 commit 7f2b2c7

9 files changed

Lines changed: 89 additions & 3 deletions

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‎config/core/300-resources/configuration.yaml‎

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@@ -1180,6 +1180,11 @@ spec:
11801180
This is accessible behind a feature flag - kubernetes.podspec-volumes-emptydir
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type: object
11821182
x-kubernetes-preserve-unknown-fields: true
1183+
ephemeral:
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description: |-
1185+
This is accessible behind a feature flag - kubernetes.podspec-volumes-ephemeral
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type: object
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x-kubernetes-preserve-unknown-fields: true
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hostPath:
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description: |-
11851190
This is accessible behind a feature flag - kubernetes.podspec-volumes-hostpath

‎config/core/300-resources/revision.yaml‎

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@@ -1156,6 +1156,11 @@ spec:
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This is accessible behind a feature flag - kubernetes.podspec-volumes-emptydir
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type: object
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x-kubernetes-preserve-unknown-fields: true
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ephemeral:
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description: |-
1161+
This is accessible behind a feature flag - kubernetes.podspec-volumes-ephemeral
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type: object
1163+
x-kubernetes-preserve-unknown-fields: true
11591164
hostPath:
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description: |-
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This is accessible behind a feature flag - kubernetes.podspec-volumes-hostpath

‎config/core/300-resources/service.yaml‎

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@@ -1198,6 +1198,11 @@ spec:
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This is accessible behind a feature flag - kubernetes.podspec-volumes-emptydir
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type: object
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x-kubernetes-preserve-unknown-fields: true
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ephemeral:
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description: |-
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This is accessible behind a feature flag - kubernetes.podspec-volumes-ephemeral
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type: object
1205+
x-kubernetes-preserve-unknown-fields: true
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hostPath:
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description: |-
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This is accessible behind a feature flag - kubernetes.podspec-volumes-hostpath

‎config/core/configmaps/features.yaml‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@ metadata:
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app.kubernetes.io/component: controller
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app.kubernetes.io/version: devel
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annotations:
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knative.dev/example-checksum: "bee75b26"
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knative.dev/example-checksum: "424df6ce"
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data:
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_example: |-
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################################
@@ -207,6 +207,12 @@ data:
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# 2. Disabled: disabling HostPath volume support
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kubernetes.podspec-volumes-hostpath: "disabled"
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210+
# Controls whether volume support for generic ephemeral volumes is enabled or not.
211+
# See https://kubernetes.io/docs/concepts/storage/ephemeral-volumes/#generic-ephemeral-volumes
212+
# 1. Enabled: enabling generic ephemeral volume support
213+
# 2. Disabled: disabling generic ephemeral volume support
214+
kubernetes.podspec-volumes-ephemeral: "disabled"
215+
210216
# Controls whether volume support for CSI is enabled or not.
211217
# 1. Enabled: enabling CSI volume support
212218
# 2. Disabled: disabling CSI volume support

‎pkg/apis/config/features.go‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -76,6 +76,7 @@ const (
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FeaturePodSpecShareProcessNamespace = "kubernetes.podspec-shareprocessnamespace"
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FeaturePodSpecTolerations = "kubernetes.podspec-tolerations"
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FeaturePodSpecTopologySpreadConstraints = "kubernetes.podspec-topologyspreadconstraints"
79+
FeaturePodSpecVolumesEphemeral = "kubernetes.podspec-volumes-ephemeral"
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FeaturePodSpecVolumesImage = "kubernetes.podspec-volumes-image"
8081
)
8182

@@ -102,6 +103,7 @@ func defaultFeaturesConfig() *Features {
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PodSpecVolumesHostPath: Disabled,
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PodSpecVolumesMountPropagation: Disabled,
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PodSpecVolumesCSI: Disabled,
106+
PodSpecVolumesEphemeral: Disabled,
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PodSpecVolumesImage: Disabled,
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PodSpecPersistentVolumeClaim: Disabled,
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PodSpecPersistentVolumeWrite: Disabled,
@@ -141,6 +143,7 @@ func NewFeaturesConfigFromMap(data map[string]string) (*Features, error) {
141143
asFlag(FeaturePodSpecHostPID, &nc.PodSpecHostPID),
142144
asFlag(FeaturePodSpecHostPath, &nc.PodSpecVolumesHostPath),
143145
asFlag(FeaturePodSpecVolumesCSI, &nc.PodSpecVolumesCSI),
146+
asFlag(FeaturePodSpecVolumesEphemeral, &nc.PodSpecVolumesEphemeral),
144147
asFlag(FeaturePodSpecVolumesImage, &nc.PodSpecVolumesImage),
145148
asFlag(FeaturePodSpecInitContainers, &nc.PodSpecInitContainers),
146149
asFlag(FeaturePodSpecVolumesMountPropagation, &nc.PodSpecVolumesMountPropagation),
@@ -187,6 +190,7 @@ type Features struct {
187190
PodSpecVolumesHostPath Flag
188191
PodSpecVolumesMountPropagation Flag
189192
PodSpecVolumesCSI Flag
193+
PodSpecVolumesEphemeral Flag
190194
PodSpecVolumesImage Flag
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PodSpecInitContainers Flag
192196
PodSpecPersistentVolumeClaim Flag

‎pkg/apis/serving/fieldmask.go‎

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Original file line numberDiff line numberDiff line change
@@ -76,6 +76,10 @@ func VolumeSourceMask(ctx context.Context, in *corev1.VolumeSource) *corev1.Volu
7676
out.CSI = in.CSI
7777
}
7878

79+
if cfg.Features.PodSpecVolumesEphemeral != config.Disabled {
80+
out.Ephemeral = in.Ephemeral
81+
}
82+
7983
if cfg.Features.PodSpecVolumesImage != config.Disabled {
8084
out.Image = in.Image
8185
}

‎pkg/apis/serving/k8s_validation.go‎

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -138,6 +138,10 @@ func validateVolume(ctx context.Context, volume corev1.Volume) *apis.FieldError
138138
errs = errs.Also(&apis.FieldError{Message: fmt.Sprintf("CSI volume support is disabled, "+
139139
"but found CSI volume %s", volume.Name)})
140140
}
141+
if volume.Ephemeral != nil && features.PodSpecVolumesEphemeral != config.Enabled {
142+
errs = errs.Also(&apis.FieldError{Message: fmt.Sprintf("Ephemeral volume support is disabled, "+
143+
"but found Ephemeral volume %s", volume.Name)})
144+
}
141145
errs = errs.Also(apis.CheckDisallowedFields(volume, *VolumeMask(ctx, &volume)))
142146
if volume.Name == "" {
143147
errs = apis.ErrMissingField("name")
@@ -182,6 +186,10 @@ func validateVolume(ctx context.Context, volume corev1.Volume) *apis.FieldError
182186
specified = append(specified, "csi")
183187
}
184188

189+
if vs.Ephemeral != nil {
190+
specified = append(specified, "ephemeral")
191+
}
192+
185193
if vs.Image != nil {
186194
specified = append(specified, "image")
187195
errs = errs.Also(validateImageVolumeSource(vs.Image).ViaField("image"))
@@ -202,6 +210,9 @@ func validateVolume(ctx context.Context, volume corev1.Volume) *apis.FieldError
202210
if cfg.Features.PodSpecVolumesCSI == config.Enabled {
203211
fieldPaths = append(fieldPaths, "csi")
204212
}
213+
if cfg.Features.PodSpecVolumesEphemeral == config.Enabled {
214+
fieldPaths = append(fieldPaths, "ephemeral")
215+
}
205216
if cfg.Features.PodSpecVolumesImage == config.Enabled {
206217
fieldPaths = append(fieldPaths, "image")
207218
}
@@ -717,7 +728,7 @@ func validateVolumeMounts(ctx context.Context, mounts []corev1.VolumeMount, volu
717728
}
718729
seenMountPath.Insert(path.Clean(vm.MountPath))
719730

720-
shouldCheckReadOnlyVolume := volumes[vm.Name].EmptyDir == nil && volumes[vm.Name].PersistentVolumeClaim == nil
731+
shouldCheckReadOnlyVolume := volumes[vm.Name].EmptyDir == nil && volumes[vm.Name].PersistentVolumeClaim == nil && volumes[vm.Name].Ephemeral == nil
721732
if shouldCheckReadOnlyVolume && !vm.ReadOnly {
722733
errs = errs.Also((&apis.FieldError{
723734
Message: "volume mount should be readOnly for this type of volume",

‎pkg/apis/serving/k8s_validation_test.go‎

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Original file line numberDiff line numberDiff line change
@@ -157,6 +157,13 @@ func withPodSpecVolumesCSIEnabled() configOption {
157157
}
158158
}
159159

160+
func withPodSpecVolumesEphemeralEnabled() configOption {
161+
return func(cfg *config.Config) *config.Config {
162+
cfg.Features.PodSpecVolumesEphemeral = config.Enabled
163+
return cfg
164+
}
165+
}
166+
160167
func withPodSpecVolumesImageEnabled() configOption {
161168
return func(cfg *config.Config) *config.Config {
162169
cfg.Features.PodSpecVolumesImage = config.Enabled
@@ -3492,6 +3499,45 @@ func TestVolumeValidation(t *testing.T) {
34923499
},
34933500
cfgOpts: []configOption{withPodSpecVolumesImageEnabled()},
34943501
want: apis.ErrMissingOneOf("secret", "configMap", "projected", "emptyDir", "image"),
3502+
}, {
3503+
name: "valid ephemeral volume with feature enabled",
3504+
v: corev1.Volume{
3505+
Name: "foo",
3506+
VolumeSource: corev1.VolumeSource{
3507+
Ephemeral: &corev1.EphemeralVolumeSource{
3508+
VolumeClaimTemplate: &corev1.PersistentVolumeClaimTemplate{
3509+
Spec: corev1.PersistentVolumeClaimSpec{
3510+
AccessModes: []corev1.PersistentVolumeAccessMode{corev1.ReadWriteOnce},
3511+
},
3512+
},
3513+
},
3514+
},
3515+
},
3516+
cfgOpts: []configOption{withPodSpecVolumesEphemeralEnabled()},
3517+
}, {
3518+
name: "ephemeral volume with feature disabled",
3519+
v: corev1.Volume{
3520+
Name: "foo",
3521+
VolumeSource: corev1.VolumeSource{
3522+
Ephemeral: &corev1.EphemeralVolumeSource{
3523+
VolumeClaimTemplate: &corev1.PersistentVolumeClaimTemplate{
3524+
Spec: corev1.PersistentVolumeClaimSpec{
3525+
AccessModes: []corev1.PersistentVolumeAccessMode{corev1.ReadWriteOnce},
3526+
},
3527+
},
3528+
},
3529+
},
3530+
},
3531+
want: (&apis.FieldError{
3532+
Message: `Ephemeral volume support is disabled, but found Ephemeral volume foo`,
3533+
}).Also(&apis.FieldError{Message: "must not set the field(s)", Paths: []string{"ephemeral"}}),
3534+
}, {
3535+
name: "missing ephemeral volume when required",
3536+
v: corev1.Volume{
3537+
Name: "foo",
3538+
},
3539+
cfgOpts: []configOption{withPodSpecVolumesEphemeralEnabled()},
3540+
want: apis.ErrMissingOneOf("secret", "configMap", "projected", "emptyDir", "ephemeral"),
34953541
}}
34963542

34973543
for _, test := range tests {

‎pkg/apis/serving/v1/revision_defaults.go‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -145,7 +145,7 @@ func (rs *RevisionSpec) applyDefault(ctx context.Context, container *corev1.Cont
145145

146146
vNames := make(sets.Set[string])
147147
for _, v := range rs.PodSpec.Volumes {
148-
if v.EmptyDir != nil || v.PersistentVolumeClaim != nil {
148+
if v.EmptyDir != nil || v.PersistentVolumeClaim != nil || v.Ephemeral != nil {
149149
vNames.Insert(v.Name)
150150
}
151151
}

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