✨ Helper for unmanaged webhook server

pkg/webhook/admission/webhook.go

@@ -27,8 +27,11 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/json"
+	"k8s.io/client-go/kubernetes/scheme"
 
+	logf "sigs.k8s.io/controller-runtime/pkg/internal/log"
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/internal/metrics"
 )
 
 var (
@@ -110,6 +113,9 @@ func (f HandlerFunc) Handle(ctx context.Context, req Request) Response {
 }
 
 // Webhook represents each individual webhook.
+//
+// It must be registered with a webhook.Server or
+// populated by StandaloneWebhook to be ran on an arbitrary HTTP server.
 type Webhook struct {
 	// Handler actually processes an admission request returning whether it was allowed or denied,
 	// and potentially patches to apply to the handler.
@@ -203,3 +209,45 @@ func (w *Webhook) InjectFunc(f inject.Func) error {
 
 	return setFields(w.Handler)
 }
+
+// StandaloneOptions let you configure a StandaloneWebhook.
+type StandaloneOptions struct {
+	// Scheme is the scheme used to resolve runtime.Objects to GroupVersionKinds / Resources
+	// Defaults to the kubernetes/client-go scheme.Scheme, but it's almost always better
+	// idea to pass your own scheme in.  See the documentation in pkg/scheme for more information.
+	Scheme *runtime.Scheme
+	// Logger to be used by the webhook.
+	// If none is set, it defaults to log.Log global logger.
+	Logger logr.Logger
+	// MetricsPath is used for labelling prometheus metrics
+	// by the path is served on.
+	// If none is set, prometheus metrics will not be generated.
+	MetricsPath string
+}
+
+// StandaloneWebhook prepares a webhook for use without a webhook.Server,
+// passing in the information normally populated by webhook.Server
+// and instrumenting the webhook with metrics.
+//
+// Use this to attach your webhook to an arbitrary HTTP server or mux.
+func StandaloneWebhook(hook *Webhook, opts StandaloneOptions) (http.Handler, error) {
+	if opts.Scheme == nil {
+		opts.Scheme = scheme.Scheme
+	}
+
+	var err error
+	hook.decoder, err = NewDecoder(opts.Scheme)
+	if err != nil {
+		return nil, err
+	}
+
+	if opts.Logger == nil {
+		opts.Logger = logf.RuntimeLog.WithName("webhook")
+	}
+	hook.log = opts.Logger
+
+	if opts.MetricsPath == "" {
+		return hook, nil
+	}
+	return metrics.InstrumentedHook(opts.MetricsPath, hook), nil
+}

pkg/webhook/example_test.go

@@ -18,18 +18,24 @@ package webhook_test
 
 import (
 	"context"
+	"net/http"
 
+	"k8s.io/client-go/kubernetes/scheme"
 	ctrl "sigs.k8s.io/controller-runtime"
+	logf "sigs.k8s.io/controller-runtime/pkg/internal/log"
+	"sigs.k8s.io/controller-runtime/pkg/manager/signals"
 	. "sigs.k8s.io/controller-runtime/pkg/webhook"
 	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
 )
 
-func Example() {
-	// Build webhooks
+var (
+	// Build webhooks used for the various server
+	// configuration options
+	//
 	// These handlers could be also be implementations
 	// of the AdmissionHandler interface for more complex
 	// implementations.
-	mutatingHook := &Admission{
+	mutatingHook = &Admission{
 		Handler: admission.HandlerFunc(func(ctx context.Context, req AdmissionRequest) AdmissionResponse {
 			return Patched("some changes",
 				JSONPatchOp{Operation: "add", Path: "/metadata/annotations/access", Value: "granted"},
@@ -38,12 +44,16 @@ func Example() {
 		}),
 	}
 
-	validatingHook := &Admission{
+	validatingHook = &Admission{
 		Handler: admission.HandlerFunc(func(ctx context.Context, req AdmissionRequest) AdmissionResponse {
 			return Denied("none shall pass!")
 		}),
 	}
+)
 
+// This example registers a webhooks to a webhook server
+// that gets ran by a controller manager.
+func Example() {
 	// Create a manager
 	// Note: GetConfigOrDie will os.Exit(1) w/o any message if no kube-config can be found
 	mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{})
@@ -70,3 +80,72 @@ func Example() {
 		panic(err)
 	}
 }
+
+// This example creates a webhook server that can be
+// ran without a controller manager.
+func ExampleServer_StartStandalone() {
+	// Create a webhook server
+	hookServer := &Server{
+		Port: 8443,
+	}
+
+	// Register the webhooks in the server.
+	hookServer.Register("/mutating", mutatingHook)
+	hookServer.Register("/validating", validatingHook)
+
+	// Start the server without a manger
+	err := hookServer.StartStandalone(signals.SetupSignalHandler(), scheme.Scheme)
+	if err != nil {
+		// handle error
+		panic(err)
+	}
+}
+
+// This example creates a standalone webhook handler
+// and runs it on a vanilla go HTTP server to demonstrate
+// how you could run a webhook on an existing server
+// without a controller manager.
+func ExampleStandaloneWebhook() {
+	// Assume you have an existing HTTP server at your disposal
+	// configured as desired (e.g. with TLS).
+	// For this example just create a basic http.ServeMux
+	mux := http.NewServeMux()
+	port := ":8000"
+
+	// Create the standalone HTTP handlers from our webhooks
+	mutatingHookHandler, err := admission.StandaloneWebhook(mutatingHook, admission.StandaloneOptions{
+		Scheme: scheme.Scheme,
+		// Logger let's you optionally pass
+		// a custom logger (defaults to log.Log global Logger)
+		Logger: logf.RuntimeLog.WithName("mutating-webhook"),
+		// MetricsPath let's you optionally
+		// provide the path it will be served on
+		// to be used for labelling prometheus metrics
+		// If none is set, prometheus metrics will not be generated.
+		MetricsPath: "/mutating",
+	})
+	if err != nil {
+		// handle error
+		panic(err)
+	}
+
+	validatingHookHandler, err := admission.StandaloneWebhook(validatingHook, admission.StandaloneOptions{
+		Scheme:      scheme.Scheme,
+		Logger:      logf.RuntimeLog.WithName("validating-webhook"),
+		MetricsPath: "/validating",
+	})
+	if err != nil {
+		// handle error
+		panic(err)
+	}
+
+	// Register the webhook handlers to your server
+	mux.Handle("/mutating", mutatingHookHandler)
+	mux.Handle("/validating", validatingHookHandler)
+
+	// Run your handler
+	if err := http.ListenAndServe(port, mux); err != nil {
+		panic(err)
+	}
+
+}

pkg/webhook/internal/metrics/metrics.go

@@ -17,7 +17,10 @@ limitations under the License.
 package metrics
 
 import (
+	"net/http"
+
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 
 	"sigs.k8s.io/controller-runtime/pkg/metrics"
 )
@@ -59,3 +62,24 @@ var (
 func init() {
 	metrics.Registry.MustRegister(RequestLatency, RequestTotal, RequestInFlight)
 }
+
+// InstrumentedHook adds some instrumentation on top of the given webhook.
+func InstrumentedHook(path string, hookRaw http.Handler) http.Handler {
+	lbl := prometheus.Labels{"webhook": path}
+
+	lat := RequestLatency.MustCurryWith(lbl)
+	cnt := RequestTotal.MustCurryWith(lbl)
+	gge := RequestInFlight.With(lbl)
+
+	// Initialize the most likely HTTP status codes.
+	cnt.WithLabelValues("200")
+	cnt.WithLabelValues("500")
+
+	return promhttp.InstrumentHandlerDuration(
+		lat,
+		promhttp.InstrumentHandlerCounter(
+			cnt,
+			promhttp.InstrumentHandlerInFlight(gge, hookRaw),
+		),
+	)
+}

pkg/webhook/server.go

@@ -29,8 +29,8 @@ import (
 	"strconv"
 	"sync"
 
-	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"k8s.io/apimachinery/pkg/runtime"
+	kscheme "k8s.io/client-go/kubernetes/scheme"
 	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
 	"sigs.k8s.io/controller-runtime/pkg/webhook/internal/metrics"
@@ -124,7 +124,7 @@ func (s *Server) Register(path string, hook http.Handler) {
 	}
 	// TODO(directxman12): call setfields if we've already started the server
 	s.webhooks[path] = hook
-	s.WebhookMux.Handle(path, instrumentedHook(path, hook))
+	s.WebhookMux.Handle(path, metrics.InstrumentedHook(path, hook))
 
 	regLog := log.WithValues("path", path)
 	regLog.Info("registering webhook")
@@ -149,25 +149,24 @@ func (s *Server) Register(path string, hook http.Handler) {
 	}
 }
 
-// instrumentedHook adds some instrumentation on top of the given webhook.
-func instrumentedHook(path string, hookRaw http.Handler) http.Handler {
-	lbl := prometheus.Labels{"webhook": path}
-
-	lat := metrics.RequestLatency.MustCurryWith(lbl)
-	cnt := metrics.RequestTotal.MustCurryWith(lbl)
-	gge := metrics.RequestInFlight.With(lbl)
-
-	// Initialize the most likely HTTP status codes.
-	cnt.WithLabelValues("200")
-	cnt.WithLabelValues("500")
-
-	return promhttp.InstrumentHandlerDuration(
-		lat,
-		promhttp.InstrumentHandlerCounter(
-			cnt,
-			promhttp.InstrumentHandlerInFlight(gge, hookRaw),
-		),
-	)
+// StartStandalone runs a webhook server without
+// a controller manager.
+func (s *Server) StartStandalone(ctx context.Context, scheme *runtime.Scheme) error {
+	// Use the Kubernetes client-go scheme if none is specified
+	if scheme == nil {
+		scheme = kscheme.Scheme
+	}
+
+	if err := s.InjectFunc(func(i interface{}) error {
+		if _, err := inject.SchemeInto(scheme, i); err != nil {
+			return err
+		}
+		return nil
+	}); err != nil {
+		return err
+	}
+
+	return s.Start(ctx)
 }
 
 // Start runs the server.

pkg/webhook/server_test.go

@@ -25,6 +25,7 @@ import (
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
+	"k8s.io/client-go/kubernetes/scheme"
 	"k8s.io/client-go/rest"
 	"sigs.k8s.io/controller-runtime/pkg/envtest"
 	"sigs.k8s.io/controller-runtime/pkg/webhook"
@@ -68,12 +69,12 @@ var _ = Describe("Webhook Server", func() {
 		Expect(servingOpts.Cleanup()).To(Succeed())
 	})
 
-	startServer := func() (done <-chan struct{}) {
+	genericStartServer := func(f func(ctx context.Context)) (done <-chan struct{}) {
 		doneCh := make(chan struct{})
 		go func() {
 			defer GinkgoRecover()
 			defer close(doneCh)
-			Expect(server.Start(ctx)).To(Succeed())
+			f(ctx)
 		}()
 		// wait till we can ping the server to start the test
 		Eventually(func() error {
@@ -93,6 +94,12 @@ var _ = Describe("Webhook Server", func() {
 		return doneCh
 	}
 
+	startServer := func() (done <-chan struct{}) {
+		return genericStartServer(func(ctx context.Context) {
+			Expect(server.Start(ctx)).To(Succeed())
+		})
+	}
+
 	// TODO(directxman12): figure out a good way to test all the serving setup
 	// with httptest.Server to get all the niceness from that.
 
@@ -174,6 +181,28 @@ var _ = Describe("Webhook Server", func() {
 			Expect(handler.injectedField).To(BeTrue())
 		})
 	})
+
+	It("should serve be able to serve in unmanaged mode", func() {
+		server = &webhook.Server{
+			Host:    servingOpts.LocalServingHost,
+			Port:    servingOpts.LocalServingPort,
+			CertDir: servingOpts.LocalServingCertDir,
+		}
+		server.Register("/somepath", &testHandler{})
+		doneCh := genericStartServer(func(ctx context.Context) {
+			Expect(server.StartStandalone(ctx, scheme.Scheme))
+		})
+
+		Eventually(func() ([]byte, error) {
+			resp, err := client.Get(fmt.Sprintf("https://%s/somepath", testHostPort))
+			Expect(err).NotTo(HaveOccurred())
+			defer resp.Body.Close()
+			return ioutil.ReadAll(resp.Body)
+		}).Should(Equal([]byte("gadzooks!")))
+
+		ctxCancel()
+		Eventually(doneCh, "4s").Should(BeClosed())
+	})
 })
 
 type testHandler struct {