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Merge pull request #3040 from liggitt/feature-gate 

Update feature gate and alpha field guidance
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Kubernetes Prow Robot 2018-12-18 15:32:13 -08:00 committed by GitHub
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contributors/devel/api_changes.md
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@ -927,8 +927,10 @@ The preferred approach adds an alpha field to the existing object, and ensures i
} }
``` ```
3. Before persisting the object to storage, clear disabled alpha fields. 3. Before persisting the object to storage, clear disabled alpha fields on create,
One possible place to do this is in the REST storage strategy's PrepareForCreate/PrepareForUpdate methods: and on update if the existing object does not already have a value in the field.
This prevents new usage of the feature while it is disabled, while ensuring existing data is preserved.
The recommended place to do this is in the REST storage strategy's PrepareForCreate/PrepareForUpdate methods:
```go ```go
func (frobberStrategy) PrepareForCreate(ctx genericapirequest.Context, obj runtime.Object) { func (frobberStrategy) PrepareForCreate(ctx genericapirequest.Context, obj runtime.Object) {
@ -943,30 +945,24 @@ One possible place to do this is in the REST storage strategy's PrepareForCreate
newFrobber := obj.(*api.Frobber) newFrobber := obj.(*api.Frobber)
oldFrobber := old.(*api.Frobber) oldFrobber := old.(*api.Frobber)
if !utilfeature.DefaultFeatureGate.Enabled(features.Frobber2D) { if !utilfeature.DefaultFeatureGate.Enabled(features.Frobber2D) && oldFrobber.Width == nil {
newFrobber.Width = nil newFrobber.Width = nil
oldFrobber.Width = nil
} }
} }
``` ```
4. In validation, ensure the alpha field is not set if the feature gate is disabled (covers cases we might miss in the above): 4. In validation, validate the field if present:
```go ```go
func ValidateFrobber(f *api.Frobber, fldPath *field.Path) field.ErrorList { func ValidateFrobber(f *api.Frobber, fldPath *field.Path) field.ErrorList {
... ...
if utilfeature.DefaultFeatureGate.Enabled(features.Frobber2D) { if f.Width != nil {
... normal validation of width field ... ... validation of width field ...
} else if f.Width != nil {
allErrs = append(allErrs, field.Forbidden(fldPath.Child("width"), "disabled by feature-gate"))
} }
... ...
} }
``` ```
Eventually, the API machinery will handle a lot of these things automatically from
declarative inputs.
In future Kubernetes versions: In future Kubernetes versions:
* if the feature progresses to beta or stable status, the feature gate can be removed or be enabled by default. * if the feature progresses to beta or stable status, the feature gate can be removed or be enabled by default.