Implementing conversion

With our model for conversion in place, it’s time to actually implement the conversion functions. We’ll create a conversion webhook for our CronJob API version v1 (Hub) to Spoke our CronJob API version v2 see:

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

The above command will generate the cronjob_conversion.go next to our cronjob_types.go file, to avoid cluttering up our main types file with extra functions.

Hub…

First, we’ll implement the hub. We’ll choose the v1 version as the hub:

project/api/v1/cronjob_conversion.go

Apache License

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() {}

… and Spokes

Then, we’ll implement our spoke, the v2 version:

project/api/v2/cronjob_conversion.go

Apache License

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

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
}

Now that we’ve got our conversions in place, all that we need to do is wire up our main to serve the webhook!