webhook

README

Knative Webhooks

Knative provides infrastructure for authoring webhooks under knative.dev/pkg/webhook and has a few built-in helpers for certain common admission control scenarios. The built-in admission controllers are:

1. Resource validation and defaulting (builds around apis.Validatable and apis.Defaultable under knative.dev/pkg/apis).
2. ConfigMap validation, which builds around similar patterns from knative.dev/pkg/configmap (in particular the store concept)

To illustrate standing up the webhook, let's start with one of these built-in admission controllers and then talk about how you can write your own admission controller.

Standing up a Webhook from an Admission Controller

We provide facilities in knative.dev/pkg/injection/sharedmain to try and eliminate much of the boilerplate involved in standing up a webhook. For this example we will show how to stand up the webhook using the built-in admission controller for validating and defaulting resources.

The code to stand up such a webhook looks roughly like this:

// Create a function matching this signature to pass into sharedmain.
func NewResourceAdmissionController(ctx context.Context, cmw configmap.Watcher) *controller.Impl {
	return resourcesemantics.NewAdmissionController(ctx,
		// Name of the resource webhook (created via yaml)
		fmt.Sprintf("resources.webhook.%s.knative.dev", system.Namespace()),

		// The path on which to serve the webhook.
		"/resource-validation",

		// The resources to validate and default.
		map[schema.GroupVersionKind]resourcesemantics.GenericCRD{
			// List the types to validate, this from knative.dev/sample-controller
			v1alpha1.SchemeGroupVersion.WithKind("AddressableService"): &v1alpha1.AddressableService{},
		},

		// A function that infuses the context passed to Validate/SetDefaults with custom metadata.
		func(ctx context.Context) context.Context {
			// Here is where you would infuse the context with state
			// (e.g. attach a store with configmap data, like knative.dev/serving attaches config-defaults)
			return ctx
		},

		// Whether to disallow unknown fields when parsing the resources' JSON.
		true,
	)
}

func main() {
	// Set up a signal context with our webhook options.
	ctx := webhook.WithOptions(signals.NewContext(), webhook.Options{
		// The name of the Kubernetes service selecting over this deployment's pods.
		ServiceName: "webhook",

		// The port on which to serve.
		Port:        8443,

		// The name of the secret containing certificate data.
		SecretName:  "webhook-certs",
	})

	sharedmain.MainWithContext(ctx, "webhook",
		// The certificate controller will ensure that the named secret (above) has
		// the appropriate shape for our webhook's admission controllers.
		certificates.NewController,

		// This invokes the method defined above to instantiate the resource admission
		// controller.
		NewResourceAdmissionController,
	)
}

There is also a config map validation admission controller built in under knative.dev/pkg/webhook/configmaps.

Writing new Admission Controllers

To implement your own admission controller akin to the resource defaulting and validation controller above, you implement a knative.dev/pkg/controller.Reconciler as with any you would with any other type of controller, but the Reconciler that gets embedded in the *controller.Impl should also implement:

// AdmissionController provides the interface for different admission controllers
type AdmissionController interface {
	// Path returns the path that this particular admission controller serves on.
	Path() string

	// Admit is the callback which is invoked when an HTTPS request comes in on Path().
	Admit(context.Context, *admissionv1beta1.AdmissionRequest) *admissionv1beta1.AdmissionResponse
}

The Reconciler part is responsible for the mutating or validating webhook configuration. The AdmissionController part is responsible for guiding request dispatch (Path()) and handling admission requests (Admit()).

Documentation

Index

• func MakeErrorStatus(reason string, args ...interface{}) *admissionv1beta1.AdmissionResponse
• func RegisterMetrics()
• func WithOptions(ctx context.Context, opt Options) context.Context
• type AdmissionController
• type Options
  • func GetOptions(ctx context.Context) *Options
• type StatsReporter
  • func NewStatsReporter() (StatsReporter, error)
• type Webhook
  • func New(ctx context.Context, controllers []AdmissionController) (webhook *Webhook, err error)
  • func (wh *Webhook) Run(stop <-chan struct{}) error
  • func (wh *Webhook) ServeHTTP(w http.ResponseWriter, r *http.Request)

Functions

func MakeErrorStatus

func MakeErrorStatus(reason string, args ...interface{}) *admissionv1beta1.AdmissionResponse

MakeErrorStatus creates an 'BadRequest' error AdmissionResponse

func RegisterMetrics

func RegisterMetrics()

func WithOptions

func WithOptions(ctx context.Context, opt Options) context.Context

WithOptions associates a set of webhook.Options with the returned context.

Types

type AdmissionController

type AdmissionController interface {
	// Path returns the path that this particular admission controller serves on.
	Path() string

	// Admit is the callback which is invoked when an HTTPS request comes in on Path().
	Admit(context.Context, *admissionv1beta1.AdmissionRequest) *admissionv1beta1.AdmissionResponse
}

AdmissionController provides the interface for different admission controllers

type Options

type Options struct {
	// ServiceName is the service name of the webhook.
	ServiceName string

	// SecretName is the name of k8s secret that contains the webhook
	// server key/cert and corresponding CA cert that signed them. The
	// server key/cert are used to serve the webhook and the CA cert
	// is provided to k8s apiserver during admission controller
	// registration.
	SecretName string

	// Port where the webhook is served. Per k8s admission
	// registration requirements this should be 443 unless there is
	// only a single port for the service.
	Port int

	// StatsReporter reports metrics about the webhook.
	// This will be automatically initialized by the constructor if left uninitialized.
	StatsReporter StatsReporter
}

Options contains the configuration for the webhook

func GetOptions

func GetOptions(ctx context.Context) *Options

GetOptions retrieves webhook.Options associated with the given context via WithOptions (above).

type StatsReporter

type StatsReporter interface {
	ReportRequest(request *admissionv1beta1.AdmissionRequest, response *admissionv1beta1.AdmissionResponse, d time.Duration) error
}

StatsReporter reports webhook metrics

func NewStatsReporter

func NewStatsReporter() (StatsReporter, error)

NewStatsReporter creaters a reporter for webhook metrics

type Webhook

type Webhook struct {
	Client  kubernetes.Interface
	Options Options
	Logger  *zap.SugaredLogger
	// contains filtered or unexported fields
}

Webhook implements the external webhook for validation of resources and configuration.

func New

func New(
	ctx context.Context,
	controllers []AdmissionController,
) (webhook *Webhook, err error)

New constructs a Webhook

func (*Webhook) Run

func (wh *Webhook) Run(stop <-chan struct{}) error

Run implements the admission controller run loop.

func (*Webhook) ServeHTTP

func (wh *Webhook) ServeHTTP(w http.ResponseWriter, r *http.Request)