实现转换

转换模型确定后，就该实际实现转换函数了。我们将为 CronJob API 的 v1（Hub）到 v2（Spoke）创建一个转换 webhook，见：

kubebuilder create webhook --group batch --version v1 --kind CronJob --conversion --spoke v2

上述命令会在 cronjob_types.go 旁边生成 cronjob_conversion.go 文件，以避免在主类型文件中堆积额外函数。

Hub…

首先实现 hub。我们选择 v1 作为 hub：

project/api/v1/cronjob_conversion.go
Apache License

Copyright 2025 The Kubernetes authors.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

package v1

Implementing the hub method is pretty easy – we just have to add an empty method called Hub()to serve as a marker. We could also just put this inline in our cronjob_types.go file.

// Hub marks this type as a conversion hub.
func (*CronJob) Hub() {}

…以及 Spokes

然后实现 spoke，即 v2 版本：

project/api/v2/cronjob_conversion.go
Apache License

Copyright 2025 The Kubernetes authors.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

package v2

Imports

For imports, we’ll need the controller-runtime conversion package, plus the API version for our hub type (v1), and finally some of the standard packages.

import (
	"fmt"
	"strings"

	"log"

	"sigs.k8s.io/controller-runtime/pkg/conversion"

	batchv1 "tutorial.kubebuilder.io/project/api/v1"
)

Our “spoke” versions need to implement the Convertible interface. Namely, they’ll need ConvertTo() and ConvertFrom() methods to convert to/from the hub version.

ConvertTo is expected to modify its argument to contain the converted object. Most of the conversion is straightforward copying, except for converting our changed field.

// ConvertTo converts this CronJob (v2) to the Hub version (v1).
func (src *CronJob) ConvertTo(dstRaw conversion.Hub) error {
	dst := dstRaw.(*batchv1.CronJob)
	log.Printf("ConvertTo: Converting CronJob from Spoke version v2 to Hub version v1;"+
		"source: %s/%s, target: %s/%s", src.Namespace, src.Name, dst.Namespace, dst.Name)

	sched := src.Spec.Schedule
	scheduleParts := []string{"*", "*", "*", "*", "*"}
	if sched.Minute != nil {
		scheduleParts[0] = string(*sched.Minute)
	}
	if sched.Hour != nil {
		scheduleParts[1] = string(*sched.Hour)
	}
	if sched.DayOfMonth != nil {
		scheduleParts[2] = string(*sched.DayOfMonth)
	}
	if sched.Month != nil {
		scheduleParts[3] = string(*sched.Month)
	}
	if sched.DayOfWeek != nil {
		scheduleParts[4] = string(*sched.DayOfWeek)
	}
	dst.Spec.Schedule = strings.Join(scheduleParts, " ")

rote conversion

The rest of the conversion is pretty rote.

	// ObjectMeta
	dst.ObjectMeta = src.ObjectMeta

	// Spec
	dst.Spec.StartingDeadlineSeconds = src.Spec.StartingDeadlineSeconds
	dst.Spec.ConcurrencyPolicy = batchv1.ConcurrencyPolicy(src.Spec.ConcurrencyPolicy)
	dst.Spec.Suspend = src.Spec.Suspend
	dst.Spec.JobTemplate = src.Spec.JobTemplate
	dst.Spec.SuccessfulJobsHistoryLimit = src.Spec.SuccessfulJobsHistoryLimit
	dst.Spec.FailedJobsHistoryLimit = src.Spec.FailedJobsHistoryLimit

	// Status
	dst.Status.Active = src.Status.Active
	dst.Status.LastScheduleTime = src.Status.LastScheduleTime

	return nil
}

ConvertFrom is expected to modify its receiver to contain the converted object. Most of the conversion is straightforward copying, except for converting our changed field.

// ConvertFrom converts the Hub version (v1) to this CronJob (v2).
func (dst *CronJob) ConvertFrom(srcRaw conversion.Hub) error {
	src := srcRaw.(*batchv1.CronJob)
	log.Printf("ConvertFrom: Converting CronJob from Hub version v1 to Spoke version v2;"+
		"source: %s/%s, target: %s/%s", src.Namespace, src.Name, dst.Namespace, dst.Name)

	schedParts := strings.Split(src.Spec.Schedule, " ")
	if len(schedParts) != 5 {
		return fmt.Errorf("invalid schedule: not a standard 5-field schedule")
	}
	partIfNeeded := func(raw string) *CronField {
		if raw == "*" {
			return nil
		}
		part := CronField(raw)
		return &part
	}
	dst.Spec.Schedule.Minute = partIfNeeded(schedParts[0])
	dst.Spec.Schedule.Hour = partIfNeeded(schedParts[1])
	dst.Spec.Schedule.DayOfMonth = partIfNeeded(schedParts[2])
	dst.Spec.Schedule.Month = partIfNeeded(schedParts[3])
	dst.Spec.Schedule.DayOfWeek = partIfNeeded(schedParts[4])

rote conversion

The rest of the conversion is pretty rote.

	// ObjectMeta
	dst.ObjectMeta = src.ObjectMeta

	// Spec
	dst.Spec.StartingDeadlineSeconds = src.Spec.StartingDeadlineSeconds
	dst.Spec.ConcurrencyPolicy = ConcurrencyPolicy(src.Spec.ConcurrencyPolicy)
	dst.Spec.Suspend = src.Spec.Suspend
	dst.Spec.JobTemplate = src.Spec.JobTemplate
	dst.Spec.SuccessfulJobsHistoryLimit = src.Spec.SuccessfulJobsHistoryLimit
	dst.Spec.FailedJobsHistoryLimit = src.Spec.FailedJobsHistoryLimit

	// Status
	dst.Status.Active = src.Status.Active
	dst.Status.LastScheduleTime = src.Status.LastScheduleTime

	return nil
}

现在转换已经就位，我们只需要把 main 连起来以提供该 webhook！