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feat(feature-gates) implement feature gates for #849 
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‎FEATURE_GATES.md

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# Feature Gates for Kubebuilder
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This document describes the feature gates functionality implemented in Kubebuilder, which allows developers to mark fields in their API types as belonging to specific feature gates.
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## Overview
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Feature gates provide a way to enable or disable experimental features in your CRDs, similar to how Kubernetes core types handle feature gates. This allows for:
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- Gradual rollout of new features
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- A/B testing of experimental functionality
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- Safe deprecation of features
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- Better control over API stability
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## Usage
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### 1. Marking Fields with Feature Gates
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In your API types, you can mark fields with feature gate annotations:
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```go
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// MyResourceSpec defines the desired state of MyResource
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type MyResourceSpec struct {
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// Standard field
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Name string `json:"name"`
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// Experimental field that requires the "experimental-feature" gate
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// +feature-gate experimental-feature
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ExperimentalField string `json:"experimentalField,omitempty"`
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// Another experimental field
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// +feature-gate another-feature
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AnotherField int `json:"anotherField,omitempty"`
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}
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```
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### 2. Running with Feature Gates
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When you run your controller, you can enable or disable feature gates:
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```bash
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# Enable all feature gates
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./manager --feature-gates=experimental-feature,another-feature
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# Enable some gates and disable others
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./manager --feature-gates=experimental-feature=true,another-feature=false
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# Disable a specific gate
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./manager --feature-gates=experimental-feature=false
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```
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### 3. Feature Gate Discovery
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Kubebuilder automatically discovers feature gates from your API types and generates validation code. The available feature gates are listed in the help text:
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```bash
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./manager --help
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```
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You'll see output like:
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```
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--feature-gates string A set of key=value pairs that describe feature gates for alpha/experimental features. Options are: experimental-feature, another-feature
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```
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## Implementation Details
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### Feature Gate Parsing
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The feature gate string follows this format:
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- `feature1` - enables feature1 (default)
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- `feature1=true` - explicitly enables feature1
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- `feature1=false` - explicitly disables feature1
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- `feature1,feature2=false,feature3` - mixed enabled/disabled gates
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### Marker Parsing
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Kubebuilder scans your API types for markers in the format:
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```
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// +feature-gate gate-name
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```
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These markers are found in:
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- Struct field comments
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- Function comments
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- Type comments
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### Validation
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The controller validates that:
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1. All specified feature gates are valid (exist in the codebase)
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2. Feature gate values are properly formatted
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3. No duplicate or conflicting gate specifications
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## Examples
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### Basic Example
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```go
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// api/v1/myresource_types.go
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type MyResourceSpec struct {
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// Standard field
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Name string `json:"name"`
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// Experimental field
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// +feature-gate alpha-feature
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AlphaField string `json:"alphaField,omitempty"`
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}
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```
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### Advanced Example
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```go
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// api/v1/complexresource_types.go
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type ComplexResourceSpec struct {
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// Standard fields
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Name string `json:"name"`
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Replicas int32 `json:"replicas"`
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// Beta feature
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// +feature-gate beta-feature
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BetaField string `json:"betaField,omitempty"`
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// Alpha feature
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// +feature-gate alpha-feature
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AlphaField string `json:"alphaField,omitempty"`
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// Experimental feature
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// +feature-gate experimental-feature
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ExperimentalField string `json:"experimentalField,omitempty"`
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}
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```
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Running with different configurations:
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```bash
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# Enable all features
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./manager --feature-gates=alpha-feature,beta-feature,experimental-feature
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# Enable only beta features
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./manager --feature-gates=beta-feature
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# Disable experimental features
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./manager --feature-gates=alpha-feature,beta-feature,experimental-feature=false
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```
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## Best Practices
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1. **Use descriptive gate names**: Choose names that clearly indicate what the feature does
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2. **Document your gates**: Add comments explaining what each feature gate enables
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3. **Gradual rollout**: Start with alpha features, then beta, then stable
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4. **Consistent naming**: Use kebab-case for feature gate names
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5. **Validation**: Always validate feature gate inputs in your controllers
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## Migration Guide
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### From No Feature Gates
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1. Add feature gate markers to your experimental fields
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2. Rebuild your project: `make manifests`
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3. Update your deployment to include the `--feature-gates` flag
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4. Test with different gate combinations
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### To Stable Features
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When a feature is ready for stable release:
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1. Remove the feature gate marker
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2. Update documentation
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3. Consider the field stable and always available
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## Troubleshooting
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### Common Issues
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1. **Unknown feature gate**: Make sure the gate name matches exactly in your code
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2. **Invalid format**: Check that your feature gate string follows the correct format
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3. **Missing validation**: Ensure your controller validates feature gates before use
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### Debugging
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Enable verbose logging to see feature gate processing:
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```bash
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./manager --feature-gates=your-gate --v=2
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```
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## Future Enhancements
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Planned improvements include:
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- CRD schema modification based on enabled gates
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- Automatic documentation generation
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- Integration with controller-runtime feature gates
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- Webhook validation based on feature gates

‎go.mod

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github.com/spf13/afero v1.14.0
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github.com/spf13/cobra v1.9.1
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github.com/spf13/pflag v1.0.7
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github.com/stretchr/testify v1.10.0
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golang.org/x/mod v0.26.0
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golang.org/x/text v0.27.0
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golang.org/x/tools v0.35.0
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require (
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github.com/Masterminds/semver/v3 v3.3.0 // indirect
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github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
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github.com/go-logr/logr v1.4.2 // indirect
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github.com/go-task/slim-sprig/v3 v3.0.0 // indirect
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github.com/google/go-cmp v0.7.0 // indirect
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github.com/google/pprof v0.0.0-20250403155104-27863c87afa6 // indirect
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github.com/inconshreveable/mousetrap v1.1.0 // indirect
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github.com/kr/pretty v0.3.1 // indirect
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github.com/pkg/errors v0.9.1 // indirect
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github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
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github.com/rogpeppe/go-internal v1.14.1 // indirect
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go.uber.org/automaxprocs v1.6.0 // indirect
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go.yaml.in/yaml/v2 v2.4.2 // indirect

‎pkg/machinery/featuregate.go

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/*
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Copyright 2025 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www/apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package machinery
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import (
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"fmt"
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"strings"
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)
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// FeatureGate represents a feature gate with its name and enabled state
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type FeatureGate struct {
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Name string
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Enabled bool
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}
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// FeatureGates represents a collection of feature gates
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type FeatureGates map[string]bool
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// ParseFeatureGates parses a comma-separated string of feature gates
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// Format: "feature1=true,feature2=false,feature3"
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// If no value is specified, the feature gate defaults to enabled
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func ParseFeatureGates(featureGates string) (FeatureGates, error) {
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if featureGates == "" {
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return make(FeatureGates), nil
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}
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gates := make(FeatureGates)
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parts := strings.Split(featureGates, ",")
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for i, part := range parts {
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part = strings.TrimSpace(part)
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if part == "" {
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// If this is the first part and it's empty, it's an error
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if i == 0 {
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return nil, fmt.Errorf("empty feature gate name")
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}
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continue
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}
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// Parse the feature gate name and value
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var name string
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var enabled bool = true // Default to enabled
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if strings.Contains(part, "=") {
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kv := strings.SplitN(part, "=", 2)
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if len(kv) != 2 {
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return nil, fmt.Errorf("invalid feature gate format: %s", part)
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}
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name = strings.TrimSpace(kv[0])
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value := strings.TrimSpace(kv[1])
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switch strings.ToLower(value) {
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case "true", "1", "yes", "on":
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enabled = true
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case "false", "0", "no", "off":
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enabled = false
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default:
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return nil, fmt.Errorf("invalid feature gate value for %s: %s", name, value)
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}
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} else {
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name = part
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}
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if name == "" {
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return nil, fmt.Errorf("empty feature gate name")
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}
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gates[name] = enabled
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}
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return gates, nil
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}
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// IsEnabled checks if a specific feature gate is enabled
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func (fg FeatureGates) IsEnabled(name string) bool {
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enabled, exists := fg[name]
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return exists && enabled
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}
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// GetEnabledGates returns a list of enabled feature gate names
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func (fg FeatureGates) GetEnabledGates() []string {
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var enabled []string
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for name, isEnabled := range fg {
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if isEnabled {
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enabled = append(enabled, name)
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}
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}
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return enabled
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}
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// GetDisabledGates returns a list of disabled feature gate names
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func (fg FeatureGates) GetDisabledGates() []string {
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var disabled []string
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for name, enabled := range fg {
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if !enabled {
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disabled = append(disabled, name)
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}
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}
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return disabled
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}
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// String returns a string representation of the feature gates
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func (fg FeatureGates) String() string {
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if len(fg) == 0 {
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return ""
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}
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var parts []string
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for name, enabled := range fg {
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if enabled {
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parts = append(parts, name)
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} else {
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parts = append(parts, fmt.Sprintf("%s=false", name))
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}
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}
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return strings.Join(parts, ",")
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}

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