Setting up the webhooks

Our conversion is in place, so all that’s left is to tell controller-runtime about our conversion.

Webhook setup…

project/internal/webhook/v1/cronjob_webhook.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.

Go imports

package v1

import (
	"context"
	"fmt"
	"github.com/robfig/cron"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/runtime/schema"
	validationutils "k8s.io/apimachinery/pkg/util/validation"
	"k8s.io/apimachinery/pkg/util/validation/field"

	"k8s.io/apimachinery/pkg/runtime"
	ctrl "sigs.k8s.io/controller-runtime"
	logf "sigs.k8s.io/controller-runtime/pkg/log"
	"sigs.k8s.io/controller-runtime/pkg/webhook"
	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"

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

Next, we’ll setup a logger for the webhooks.

var cronjoblog = logf.Log.WithName("cronjob-resource")

This setup doubles as setup for our conversion webhooks: as long as our types implement the Hub and Convertible interfaces, a conversion webhook will be registered.

// SetupCronJobWebhookWithManager registers the webhook for CronJob in the manager.
func SetupCronJobWebhookWithManager(mgr ctrl.Manager) error {
	return ctrl.NewWebhookManagedBy(mgr).For(&batchv1.CronJob{}).
		WithValidator(&CronJobCustomValidator{}).
		WithDefaulter(&CronJobCustomDefaulter{
			DefaultConcurrencyPolicy:          batchv1.AllowConcurrent,
			DefaultSuspend:                    false,
			DefaultSuccessfulJobsHistoryLimit: 3,
			DefaultFailedJobsHistoryLimit:     1,
		}).
		Complete()
}

Notice that we use kubebuilder markers to generate webhook manifests. This marker is responsible for generating a mutating webhook manifest.

The meaning of each marker can be found here.

This marker is responsible for generating a mutation webhook manifest.

// +kubebuilder:webhook:path=/mutate-batch-tutorial-kubebuilder-io-v1-cronjob,mutating=true,failurePolicy=fail,sideEffects=None,groups=batch.tutorial.kubebuilder.io,resources=cronjobs,verbs=create;update,versions=v1,name=mcronjob-v1.kb.io,admissionReviewVersions=v1

// CronJobCustomDefaulter struct is responsible for setting default values on the custom resource of the
// Kind CronJob when those are created or updated.
//
// NOTE: The +kubebuilder:object:generate=false marker prevents controller-gen from generating DeepCopy methods,
// as it is used only for temporary operations and does not need to be deeply copied.
type CronJobCustomDefaulter struct {

	// Default values for various CronJob fields
	DefaultConcurrencyPolicy          batchv1.ConcurrencyPolicy
	DefaultSuspend                    bool
	DefaultSuccessfulJobsHistoryLimit int32
	DefaultFailedJobsHistoryLimit     int32
}

var _ webhook.CustomDefaulter = &CronJobCustomDefaulter{}

We use the webhook.CustomDefaulterinterface to set defaults to our CRD. A webhook will automatically be served that calls this defaulting.

The Defaultmethod is expected to mutate the receiver, setting the defaults.

// Default implements webhook.CustomDefaulter so a webhook will be registered for the Kind CronJob.
func (d *CronJobCustomDefaulter) Default(ctx context.Context, obj runtime.Object) error {
	cronjob, ok := obj.(*batchv1.CronJob)

	if !ok {
		return fmt.Errorf("expected an CronJob object but got %T", obj)
	}
	cronjoblog.Info("Defaulting for CronJob", "name", cronjob.GetName())

	// Set default values
	d.applyDefaults(cronjob)
	return nil
}

// applyDefaults applies default values to CronJob fields.
func (d *CronJobCustomDefaulter) applyDefaults(cronJob *batchv1.CronJob) {
	if cronJob.Spec.ConcurrencyPolicy == "" {
		cronJob.Spec.ConcurrencyPolicy = d.DefaultConcurrencyPolicy
	}
	if cronJob.Spec.Suspend == nil {
		cronJob.Spec.Suspend = new(bool)
		*cronJob.Spec.Suspend = d.DefaultSuspend
	}
	if cronJob.Spec.SuccessfulJobsHistoryLimit == nil {
		cronJob.Spec.SuccessfulJobsHistoryLimit = new(int32)
		*cronJob.Spec.SuccessfulJobsHistoryLimit = d.DefaultSuccessfulJobsHistoryLimit
	}
	if cronJob.Spec.FailedJobsHistoryLimit == nil {
		cronJob.Spec.FailedJobsHistoryLimit = new(int32)
		*cronJob.Spec.FailedJobsHistoryLimit = d.DefaultFailedJobsHistoryLimit
	}
}

We can validate our CRD beyond what’s possible with declarative validation. Generally, declarative validation should be sufficient, but sometimes more advanced use cases call for complex validation.

For instance, we’ll see below that we use this to validate a well-formed cron schedule without making up a long regular expression.

If webhook.CustomValidator interface is implemented, a webhook will automatically be served that calls the validation.

The ValidateCreate, ValidateUpdate and ValidateDelete methods are expected to validate its receiver upon creation, update and deletion respectively. We separate out ValidateCreate from ValidateUpdate to allow behavior like making certain fields immutable, so that they can only be set on creation. ValidateDelete is also separated from ValidateUpdate to allow different validation behavior on deletion. Here, however, we just use the same shared validation for ValidateCreate and ValidateUpdate. And we do nothing in ValidateDelete, since we don’t need to validate anything on deletion.

This marker is responsible for generating a validation webhook manifest.

// +kubebuilder:webhook:path=/validate-batch-tutorial-kubebuilder-io-v1-cronjob,mutating=false,failurePolicy=fail,sideEffects=None,groups=batch.tutorial.kubebuilder.io,resources=cronjobs,verbs=create;update,versions=v1,name=vcronjob-v1.kb.io,admissionReviewVersions=v1

// CronJobCustomValidator struct is responsible for validating the CronJob resource
// when it is created, updated, or deleted.
//
// NOTE: The +kubebuilder:object:generate=false marker prevents controller-gen from generating DeepCopy methods,
// as this struct is used only for temporary operations and does not need to be deeply copied.
type CronJobCustomValidator struct {
	// TODO(user): Add more fields as needed for validation
}

var _ webhook.CustomValidator = &CronJobCustomValidator{}

// ValidateCreate implements webhook.CustomValidator so a webhook will be registered for the type CronJob.
func (v *CronJobCustomValidator) ValidateCreate(ctx context.Context, obj runtime.Object) (admission.Warnings, error) {
	cronjob, ok := obj.(*batchv1.CronJob)
	if !ok {
		return nil, fmt.Errorf("expected a CronJob object but got %T", obj)
	}
	cronjoblog.Info("Validation for CronJob upon creation", "name", cronjob.GetName())

	return nil, validateCronJob(cronjob)
}

// ValidateUpdate implements webhook.CustomValidator so a webhook will be registered for the type CronJob.
func (v *CronJobCustomValidator) ValidateUpdate(ctx context.Context, oldObj, newObj runtime.Object) (admission.Warnings, error) {
	cronjob, ok := newObj.(*batchv1.CronJob)
	if !ok {
		return nil, fmt.Errorf("expected a CronJob object for the newObj but got %T", newObj)
	}
	cronjoblog.Info("Validation for CronJob upon update", "name", cronjob.GetName())

	return nil, validateCronJob(cronjob)
}

// ValidateDelete implements webhook.CustomValidator so a webhook will be registered for the type CronJob.
func (v *CronJobCustomValidator) ValidateDelete(ctx context.Context, obj runtime.Object) (admission.Warnings, error) {
	cronjob, ok := obj.(*batchv1.CronJob)
	if !ok {
		return nil, fmt.Errorf("expected a CronJob object but got %T", obj)
	}
	cronjoblog.Info("Validation for CronJob upon deletion", "name", cronjob.GetName())

	// TODO(user): fill in your validation logic upon object deletion.

	return nil, nil
}

We validate the name and the spec of the CronJob.

// validateCronJob validates the fields of a CronJob object.
func validateCronJob(cronjob *batchv1.CronJob) error {
	var allErrs field.ErrorList
	if err := validateCronJobName(cronjob); err != nil {
		allErrs = append(allErrs, err)
	}
	if err := validateCronJobSpec(cronjob); err != nil {
		allErrs = append(allErrs, err)
	}
	if len(allErrs) == 0 {
		return nil
	}

	return apierrors.NewInvalid(
		schema.GroupKind{Group: "batch.tutorial.kubebuilder.io", Kind: "CronJob"},
		cronjob.Name, allErrs)
}

Some fields are declaratively validated by OpenAPI schema. You can find kubebuilder validation markers (prefixed with // +kubebuilder:validation) in the Designing an API section. You can find all of the kubebuilder supported markers for declaring validation by running controller-gen crd -w, or here.

func validateCronJobSpec(cronjob *batchv1.CronJob) *field.Error {
	// The field helpers from the kubernetes API machinery help us return nicely
	// structured validation errors.
	return validateScheduleFormat(
		cronjob.Spec.Schedule,
		field.NewPath("spec").Child("schedule"))
}

We’ll need to validate the cron schedule is well-formatted.

func validateScheduleFormat(schedule string, fldPath *field.Path) *field.Error {
	if _, err := cron.ParseStandard(schedule); err != nil {
		return field.Invalid(fldPath, schedule, err.Error())
	}
	return nil
}

Validate object name

Validating the length of a string field can be done declaratively by the validation schema.

But the ObjectMeta.Name field is defined in a shared package under the apimachinery repo, so we can’t declaratively validate it using the validation schema.

func validateCronJobName(cronjob *batchv1.CronJob) *field.Error {
	if len(cronjob.ObjectMeta.Name) > validationutils.DNS1035LabelMaxLength-11 {
		// The job name length is 63 characters like all Kubernetes objects
		// (which must fit in a DNS subdomain). The cronjob controller appends
		// a 11-character suffix to the cronjob (`-$TIMESTAMP`) when creating
		// a job. The job name length limit is 63 characters. Therefore cronjob
		// names must have length <= 63-11=52. If we don't validate this here,
		// then job creation will fail later.
		return field.Invalid(field.NewPath("metadata").Child("name"), cronjob.ObjectMeta.Name, "must be no more than 52 characters")
	}
	return nil
}

…and `main.go`

Similarly, our existing main file is sufficient:

project/cmd/main.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

Imports

package main

import (
	"crypto/tls"
	"flag"
	"os"
	"path/filepath"

	// Import all Kubernetes client auth plugins (e.g. Azure, GCP, OIDC, etc.)
	// to ensure that exec-entrypoint and run can make use of them.
	_ "k8s.io/client-go/plugin/pkg/client/auth"

	kbatchv1 "k8s.io/api/batch/v1"
	"k8s.io/apimachinery/pkg/runtime"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	clientgoscheme "k8s.io/client-go/kubernetes/scheme"
	ctrl "sigs.k8s.io/controller-runtime"
	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
	"sigs.k8s.io/controller-runtime/pkg/healthz"
	"sigs.k8s.io/controller-runtime/pkg/log/zap"
	"sigs.k8s.io/controller-runtime/pkg/metrics/filters"
	metricsserver "sigs.k8s.io/controller-runtime/pkg/metrics/server"
	"sigs.k8s.io/controller-runtime/pkg/webhook"

	batchv1 "tutorial.kubebuilder.io/project/api/v1"
	batchv2 "tutorial.kubebuilder.io/project/api/v2"
	"tutorial.kubebuilder.io/project/internal/controller"
	webhookbatchv1 "tutorial.kubebuilder.io/project/internal/webhook/v1"
	webhookbatchv2 "tutorial.kubebuilder.io/project/internal/webhook/v2"
	// +kubebuilder:scaffold:imports
)

existing setup

var (
	scheme   = runtime.NewScheme()
	setupLog = ctrl.Log.WithName("setup")
)

func init() {
	utilruntime.Must(clientgoscheme.AddToScheme(scheme))

	utilruntime.Must(kbatchv1.AddToScheme(scheme)) // we've added this ourselves
	utilruntime.Must(batchv1.AddToScheme(scheme))
	utilruntime.Must(batchv2.AddToScheme(scheme))
	// +kubebuilder:scaffold:scheme
}

func main() {

existing setup

	var metricsAddr string
	var metricsCertPath, metricsCertName, metricsCertKey string
	var webhookCertPath, webhookCertName, webhookCertKey string
	var enableLeaderElection bool
	var probeAddr string
	var secureMetrics bool
	var enableHTTP2 bool
	var tlsOpts []func(*tls.Config)
	flag.StringVar(&metricsAddr, "metrics-bind-address", "0", "The address the metrics endpoint binds to. "+
		"Use :8443 for HTTPS or :8080 for HTTP, or leave as 0 to disable the metrics service.")
	flag.StringVar(&probeAddr, "health-probe-bind-address", ":8081", "The address the probe endpoint binds to.")
	flag.BoolVar(&enableLeaderElection, "leader-elect", false,
		"Enable leader election for controller manager. "+
			"Enabling this will ensure there is only one active controller manager.")
	flag.BoolVar(&secureMetrics, "metrics-secure", true,
		"If set, the metrics endpoint is served securely via HTTPS. Use --metrics-secure=false to use HTTP instead.")
	flag.StringVar(&webhookCertPath, "webhook-cert-path", "", "The directory that contains the webhook certificate.")
	flag.StringVar(&webhookCertName, "webhook-cert-name", "tls.crt", "The name of the webhook certificate file.")
	flag.StringVar(&webhookCertKey, "webhook-cert-key", "tls.key", "The name of the webhook key file.")
	flag.StringVar(&metricsCertPath, "metrics-cert-path", "", "The directory that contains the metrics server certificate.")
	flag.StringVar(&metricsCertName, "metrics-cert-name", "tls.crt", "The name of the metrics server certificate file.")
	flag.StringVar(&metricsCertKey, "metrics-cert-key", "tls.key", "The name of the metrics server key file.")
	flag.BoolVar(&enableHTTP2, "enable-http2", false,
		"If set, HTTP/2 will be enabled for the metrics and webhook servers")
	opts := zap.Options{
		Development: true,
	}
	opts.BindFlags(flag.CommandLine)
	flag.Parse()

	ctrl.SetLogger(zap.New(zap.UseFlagOptions(&opts)))

	// if the enable-http2 flag is false (the default), http/2 should be disabled
	// due to its vulnerabilities. More specifically, disabling http/2 will
	// prevent from being vulnerable to the HTTP/2 Stream Cancellation and
	// Rapid Reset CVEs. For more information see:
	// - https://github.com/advisories/GHSA-qppj-fm5r-hxr3
	// - https://github.com/advisories/GHSA-4374-p667-p6c8
	disableHTTP2 := func(c *tls.Config) {
		setupLog.Info("disabling http/2")
		c.NextProtos = []string{"http/1.1"}
	}

	if !enableHTTP2 {
		tlsOpts = append(tlsOpts, disableHTTP2)
	}

	// Create watchers for metrics and webhooks certificates
	var metricsCertWatcher, webhookCertWatcher *certwatcher.CertWatcher

	// Initial webhook TLS options
	webhookTLSOpts := tlsOpts

	if len(webhookCertPath) > 0 {
		setupLog.Info("Initializing webhook certificate watcher using provided certificates",
			"webhook-cert-path", webhookCertPath, "webhook-cert-name", webhookCertName, "webhook-cert-key", webhookCertKey)

		var err error
		webhookCertWatcher, err = certwatcher.New(
			filepath.Join(webhookCertPath, webhookCertName),
			filepath.Join(webhookCertPath, webhookCertKey),
		)
		if err != nil {
			setupLog.Error(err, "Failed to initialize webhook certificate watcher")
			os.Exit(1)
		}

		webhookTLSOpts = append(webhookTLSOpts, func(config *tls.Config) {
			config.GetCertificate = webhookCertWatcher.GetCertificate
		})
	}

	webhookServer := webhook.NewServer(webhook.Options{
		TLSOpts: webhookTLSOpts,
	})

	// Metrics endpoint is enabled in 'config/default/kustomization.yaml'. The Metrics options configure the server.
	// More info:
	// - https://pkg.go.dev/sigs.k8s.io/controller-runtime@v0.19.1/pkg/metrics/server
	// - https://book.kubebuilder.io/reference/metrics.html
	metricsServerOptions := metricsserver.Options{
		BindAddress:   metricsAddr,
		SecureServing: secureMetrics,
		TLSOpts:       tlsOpts,
	}

	if secureMetrics {
		// FilterProvider is used to protect the metrics endpoint with authn/authz.
		// These configurations ensure that only authorized users and service accounts
		// can access the metrics endpoint. The RBAC are configured in 'config/rbac/kustomization.yaml'. More info:
		// https://pkg.go.dev/sigs.k8s.io/controller-runtime@v0.19.1/pkg/metrics/filters#WithAuthenticationAndAuthorization
		metricsServerOptions.FilterProvider = filters.WithAuthenticationAndAuthorization
	}

	// If the certificate is not specified, controller-runtime will automatically
	// generate self-signed certificates for the metrics server. While convenient for development and testing,
	// this setup is not recommended for production.
	//
	// TODO(user): If you enable certManager, uncomment the following lines:
	// - [METRICS-WITH-CERTS] at config/default/kustomization.yaml to generate and use certificates
	// managed by cert-manager for the metrics server.
	// - [PROMETHEUS-WITH-CERTS] at config/prometheus/kustomization.yaml for TLS certification.
	if len(metricsCertPath) > 0 {
		setupLog.Info("Initializing metrics certificate watcher using provided certificates",
			"metrics-cert-path", metricsCertPath, "metrics-cert-name", metricsCertName, "metrics-cert-key", metricsCertKey)

		var err error
		metricsCertWatcher, err = certwatcher.New(
			filepath.Join(metricsCertPath, metricsCertName),
			filepath.Join(metricsCertPath, metricsCertKey),
		)
		if err != nil {
			setupLog.Error(err, "to initialize metrics certificate watcher", "error", err)
			os.Exit(1)
		}

		metricsServerOptions.TLSOpts = append(metricsServerOptions.TLSOpts, func(config *tls.Config) {
			config.GetCertificate = metricsCertWatcher.GetCertificate
		})
	}

	mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
		Scheme:                 scheme,
		Metrics:                metricsServerOptions,
		WebhookServer:          webhookServer,
		HealthProbeBindAddress: probeAddr,
		LeaderElection:         enableLeaderElection,
		LeaderElectionID:       "80807133.tutorial.kubebuilder.io",
		// LeaderElectionReleaseOnCancel defines if the leader should step down voluntarily
		// when the Manager ends. This requires the binary to immediately end when the
		// Manager is stopped, otherwise, this setting is unsafe. Setting this significantly
		// speeds up voluntary leader transitions as the new leader don't have to wait
		// LeaseDuration time first.
		//
		// In the default scaffold provided, the program ends immediately after
		// the manager stops, so would be fine to enable this option. However,
		// if you are doing or is intended to do any operation such as perform cleanups
		// after the manager stops then its usage might be unsafe.
		// LeaderElectionReleaseOnCancel: true,
	})
	if err != nil {
		setupLog.Error(err, "unable to start manager")
		os.Exit(1)
	}

	if err = (&controller.CronJobReconciler{
		Client: mgr.GetClient(),
		Scheme: mgr.GetScheme(),
	}).SetupWithManager(mgr); err != nil {
		setupLog.Error(err, "unable to create controller", "controller", "CronJob")
		os.Exit(1)
	}

Our existing call to SetupWebhookWithManager registers our conversion webhooks with the manager, too.

	// nolint:goconst
	if os.Getenv("ENABLE_WEBHOOKS") != "false" {
		if err = webhookbatchv1.SetupCronJobWebhookWithManager(mgr); err != nil {
			setupLog.Error(err, "unable to create webhook", "webhook", "CronJob")
			os.Exit(1)
		}
	}
	// nolint:goconst
	if os.Getenv("ENABLE_WEBHOOKS") != "false" {
		if err = webhookbatchv2.SetupCronJobWebhookWithManager(mgr); err != nil {
			setupLog.Error(err, "unable to create webhook", "webhook", "CronJob")
			os.Exit(1)
		}
	}
	// +kubebuilder:scaffold:builder

existing setup

	if metricsCertWatcher != nil {
		setupLog.Info("Adding metrics certificate watcher to manager")
		if err := mgr.Add(metricsCertWatcher); err != nil {
			setupLog.Error(err, "unable to add metrics certificate watcher to manager")
			os.Exit(1)
		}
	}

	if webhookCertWatcher != nil {
		setupLog.Info("Adding webhook certificate watcher to manager")
		if err := mgr.Add(webhookCertWatcher); err != nil {
			setupLog.Error(err, "unable to add webhook certificate watcher to manager")
			os.Exit(1)
		}
	}

	if err := mgr.AddHealthzCheck("healthz", healthz.Ping); err != nil {
		setupLog.Error(err, "unable to set up health check")
		os.Exit(1)
	}
	if err := mgr.AddReadyzCheck("readyz", healthz.Ping); err != nil {
		setupLog.Error(err, "unable to set up ready check")
		os.Exit(1)
	}

	setupLog.Info("starting manager")
	if err := mgr.Start(ctrl.SetupSignalHandler()); err != nil {
		setupLog.Error(err, "problem running manager")
		os.Exit(1)
	}

Everything’s set up and ready to go! All that’s left now is to test out our webhooks.

Setting up the webhooks

Webhook setup…

…and main.go

…and `main.go`