Merge pull request #45919 from ericchiang/audit-webhook-backend

Automatic merge from submit-queue

apiserver: add a webhook implementation of the audit backend

This builds off of #45315 and is intended to implement an interfaced defined in #45766.

TODO:

- [x] Rebase on top of API types PR.
- [x] Rebase on top of API types updates (#46065)
- [x] Rebase on top of feature flag (#46009)
- [x] Rebase on top of audit instrumentation.
- [x] Hook up API server flag or register plugin (depending on #45766)

Features issue https://github.com/kubernetes/features/issues/22

Design proposal https://github.com/kubernetes/community/blob/master/contributors/design-proposals/auditing.md

```release-notes
Webhook added to the API server which omits structured audit log events.
```

/cc @soltysh @timstclair @soltysh @deads2k

cmd/kube-apiserver/app/options/options.go

@@ -45,7 +45,7 @@ type ServerRunOptions struct {
 	Etcd                    *genericoptions.EtcdOptions
 	SecureServing           *genericoptions.SecureServingOptions
 	InsecureServing         *kubeoptions.InsecureServingOptions
-	Audit                   *genericoptions.AuditLogOptions
+	Audit                   *genericoptions.AuditOptions
 	Features                *genericoptions.FeatureOptions
 	Admission               *genericoptions.AdmissionOptions
 	Authentication          *kubeoptions.BuiltInAuthenticationOptions
@@ -79,7 +79,7 @@ func NewServerRunOptions() *ServerRunOptions {
 		Etcd:                 genericoptions.NewEtcdOptions(storagebackend.NewDefaultConfig(kubeoptions.DefaultEtcdPathPrefix, api.Scheme, nil)),
 		SecureServing:        kubeoptions.NewSecureServingOptions(),
 		InsecureServing:      kubeoptions.NewInsecureServingOptions(),
-		Audit:                genericoptions.NewAuditLogOptions(),
+		Audit:                genericoptions.NewAuditOptions(),
 		Features:             genericoptions.NewFeatureOptions(),
 		Admission:            genericoptions.NewAdmissionOptions(),
 		Authentication:       kubeoptions.NewBuiltInAuthenticationOptions().WithAll(),

federation/cmd/federation-apiserver/app/options/options.go

@@ -37,7 +37,7 @@ type ServerRunOptions struct {
 	Etcd                    *genericoptions.EtcdOptions
 	SecureServing           *genericoptions.SecureServingOptions
 	InsecureServing         *kubeoptions.InsecureServingOptions
-	Audit                   *genericoptions.AuditLogOptions
+	Audit                   *genericoptions.AuditOptions
 	Features                *genericoptions.FeatureOptions
 	Admission               *genericoptions.AdmissionOptions
 	Authentication          *kubeoptions.BuiltInAuthenticationOptions
@@ -56,7 +56,7 @@ func NewServerRunOptions() *ServerRunOptions {
 		Etcd:                 genericoptions.NewEtcdOptions(storagebackend.NewDefaultConfig(kubeoptions.DefaultEtcdPathPrefix, api.Scheme, nil)),
 		SecureServing:        kubeoptions.NewSecureServingOptions(),
 		InsecureServing:      kubeoptions.NewInsecureServingOptions(),
-		Audit:                genericoptions.NewAuditLogOptions(),
+		Audit:                genericoptions.NewAuditOptions(),
 		Features:             genericoptions.NewFeatureOptions(),
 		Admission:            genericoptions.NewAdmissionOptions(),
 		Authentication:       kubeoptions.NewBuiltInAuthenticationOptions().WithAll(),

hack/.linted_packages

@@ -359,6 +359,7 @@ staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory
 staging/src/k8s.io/apiserver/pkg/storage/value/encrypt/aes
 staging/src/k8s.io/apiserver/pkg/util/flushwriter
 staging/src/k8s.io/apiserver/pkg/util/logs
+staging/src/k8s.io/apiserver/plugin/pkg/audit/webhook
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator/password
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator/password/allow

hack/verify-flags/known-flags.txt

@@ -46,6 +46,8 @@ audit-log-maxage
 audit-log-maxbackup
 audit-log-maxsize
 audit-log-path
+audit-webhook-config-file
+audit-webhook-mode
 authentication-kubeconfig
 authentication-token-webhook
 authentication-token-webhook-cache-ttl

staging/src/k8s.io/apiserver/pkg/audit/BUILD

@@ -5,6 +5,7 @@ licenses(["notice"])
 load(
     "@io_bazel_rules_go//go:def.bzl",
     "go_library",
+    "go_test",
 )
 
 go_library(
@@ -13,6 +14,7 @@ go_library(
         "request.go",
         "scheme.go",
         "types.go",
+        "union.go",
     ],
     tags = ["automanaged"],
     deps = [
@@ -23,6 +25,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime/serializer:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/types:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/errors:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/net:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/apis/audit:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/apis/audit/v1alpha1:go_default_library",
@@ -30,3 +33,14 @@ go_library(
         "//vendor/k8s.io/client-go/pkg/apis/authentication/v1:go_default_library",
     ],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["union_test.go"],
+    library = ":go_default_library",
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/k8s.io/apimachinery/pkg/types:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit:go_default_library",
+    ],
+)

staging/src/k8s.io/apiserver/pkg/audit/union.go

@@ -0,0 +1,51 @@
+/*
+Copyright 2017 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 audit
+
+import (
+	"k8s.io/apimachinery/pkg/util/errors"
+	auditinternal "k8s.io/apiserver/pkg/apis/audit"
+)
+
+// Union returns an audit Backend which logs events to a set of backends. The returned
+// Sink implementation blocks in turn for each call to ProcessEvents.
+func Union(backends ...Backend) Backend {
+	if len(backends) == 1 {
+		return backends[0]
+	}
+	return union{backends}
+}
+
+type union struct {
+	backends []Backend
+}
+
+func (u union) ProcessEvents(events ...*auditinternal.Event) {
+	for _, backend := range u.backends {
+		backend.ProcessEvents(events...)
+	}
+}
+
+func (u union) Run(stopCh <-chan struct{}) error {
+	var funcs []func() error
+	for _, backend := range u.backends {
+		funcs = append(funcs, func() error {
+			return backend.Run(stopCh)
+		})
+	}
+	return errors.AggregateGoroutines(funcs...)
+}

staging/src/k8s.io/apiserver/pkg/audit/union_test.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2017 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 audit
+
+import (
+	"strconv"
+	"testing"
+
+	"k8s.io/apimachinery/pkg/types"
+	auditinternal "k8s.io/apiserver/pkg/apis/audit"
+)
+
+type fakeBackend struct {
+	events []*auditinternal.Event
+}
+
+func (f *fakeBackend) ProcessEvents(events ...*auditinternal.Event) {
+	f.events = append(f.events, events...)
+}
+
+func (f *fakeBackend) Run(stopCh <-chan struct{}) error {
+	return nil
+}
+
+func TestUnion(t *testing.T) {
+	backends := []Backend{
+		new(fakeBackend),
+		new(fakeBackend),
+		new(fakeBackend),
+	}
+
+	b := Union(backends...)
+
+	n := 5
+
+	var events []*auditinternal.Event
+	for i := 0; i < n; i++ {
+		events = append(events, &auditinternal.Event{
+			AuditID: types.UID(strconv.Itoa(i)),
+		})
+	}
+	b.ProcessEvents(events...)
+
+	for i, b := range backends {
+		// so we can inspect the underlying events.
+		backend := b.(*fakeBackend)
+
+		if got := len(backend.events); got != n {
+			t.Errorf("backend %d wanted %d events, got %d", i, n, got)
+			continue
+		}
+		for j, event := range backend.events {
+			wantID := types.UID(strconv.Itoa(j))
+			if event.AuditID != wantID {
+				t.Errorf("backend %d event %d wanted id %s, got %s", i, j, wantID, event.AuditID)
+			}
+		}
+	}
+}

staging/src/k8s.io/apiserver/pkg/server/options/BUILD

@@ -54,6 +54,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/util/net:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/admission:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/admission/initializer:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/audit:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/audit/policy:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/authentication/authenticatorfactory:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/authorization/authorizerfactory:go_default_library",
@@ -66,6 +67,7 @@ go_library(
         "//vendor/k8s.io/apiserver/pkg/util/feature:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/util/flag:go_default_library",
         "//vendor/k8s.io/apiserver/plugin/pkg/audit/log:go_default_library",
+        "//vendor/k8s.io/apiserver/plugin/pkg/audit/webhook:go_default_library",
         "//vendor/k8s.io/client-go/informers:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes/typed/authentication/v1beta1:go_default_library",

staging/src/k8s.io/apiserver/pkg/server/options/audit.go

@@ -20,28 +20,106 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strings"
 
 	"github.com/spf13/pflag"
 	"gopkg.in/natefinch/lumberjack.v2"
 
+	"k8s.io/apiserver/pkg/audit"
 	"k8s.io/apiserver/pkg/audit/policy"
 	"k8s.io/apiserver/pkg/features"
 	"k8s.io/apiserver/pkg/server"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	pluginlog "k8s.io/apiserver/plugin/pkg/audit/log"
+	pluginwebhook "k8s.io/apiserver/plugin/pkg/audit/webhook"
 )
 
+func appendBackend(existing, newBackend audit.Backend) audit.Backend {
+	if existing == nil {
+		return newBackend
+	}
+	return audit.Union(existing, newBackend)
+}
+
+func advancedAuditingEnabled() bool {
+	return utilfeature.DefaultFeatureGate.Enabled(features.AdvancedAuditing)
+}
+
+type AuditOptions struct {
+	// Policy configuration file for filtering audit events that are captured.
+	// If unspecified, a default is provided.
+	PolicyFile string
+
+	// Plugin options
+
+	LogOptions     AuditLogOptions
+	WebhookOptions AuditWebhookOptions
+}
+
+// AuditLogOptions holds the legacy audit log writer. If the AdvancedAuditing feature
+// is enabled, these options determine the output of the structured audit log.
 type AuditLogOptions struct {
 	Path       string
 	MaxAge     int
 	MaxBackups int
 	MaxSize    int
-
-	PolicyFile string
 }
 
-func NewAuditLogOptions() *AuditLogOptions {
-	return &AuditLogOptions{}
+// AuditWebhookOptions control the webhook configuration for audit events.
+type AuditWebhookOptions struct {
+	ConfigFile string
+	// Should the webhook asynchronous batch events to the webhook backend or
+	// should the webhook block responses?
+	//
+	// Defaults to asynchronous batch events.
+	Mode string
+}
+
+func NewAuditOptions() *AuditOptions {
+	return &AuditOptions{
+		WebhookOptions: AuditWebhookOptions{Mode: pluginwebhook.ModeBatch},
+	}
+}
+
+func (o *AuditOptions) AddFlags(fs *pflag.FlagSet) {
+	fs.StringVar(&o.PolicyFile, "audit-policy-file", o.PolicyFile,
+		"Path to the file that defines the audit policy configuration. Requires the 'AdvancedAuditing' feature gate."+
+			" With AdvancedAuditing, a profile is required to enable auditing.")
+
+	o.LogOptions.AddFlags(fs)
+	o.WebhookOptions.AddFlags(fs)
+}
+
+func (o *AuditOptions) ApplyTo(c *server.Config) error {
+	// Apply generic options.
+	if err := o.applyTo(c); err != nil {
+		return err
+	}
+
+	// Apply plugin options.
+	if err := o.LogOptions.applyTo(c); err != nil {
+		return err
+	}
+	if err := o.WebhookOptions.applyTo(c); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (o *AuditOptions) applyTo(c *server.Config) error {
+	if o.PolicyFile == "" {
+		return nil
+	}
+
+	if !advancedAuditingEnabled() {
+		return fmt.Errorf("feature '%s' must be enabled to set an audit policy", features.AdvancedAuditing)
+	}
+	p, err := policy.LoadPolicyFromFile(o.PolicyFile)
+	if err != nil {
+		return fmt.Errorf("loading audit policy file: %v", err)
+	}
+	c.AuditPolicyChecker = policy.NewChecker(p)
+	return nil
 }
 
 func (o *AuditLogOptions) AddFlags(fs *pflag.FlagSet) {
@@ -53,29 +131,10 @@ func (o *AuditLogOptions) AddFlags(fs *pflag.FlagSet) {
 		"The maximum number of old audit log files to retain.")
 	fs.IntVar(&o.MaxSize, "audit-log-maxsize", o.MaxSize,
 		"The maximum size in megabytes of the audit log file before it gets rotated.")
-
-	fs.StringVar(&o.PolicyFile, "audit-policy-file", o.PolicyFile,
-		"Path to the file that defines the audit policy configuration. Requires the 'AdvancedAuditing' feature gate."+
-			" With AdvancedAuditing, a profile is required to enable auditing.")
 }
 
-func (o *AuditLogOptions) ApplyTo(c *server.Config) error {
-	if utilfeature.DefaultFeatureGate.Enabled(features.AdvancedAuditing) {
-		if o.PolicyFile != "" {
-			p, err := policy.LoadPolicyFromFile(o.PolicyFile)
-			if err != nil {
-				return err
-			}
-			c.AuditPolicyChecker = policy.NewChecker(p)
-		}
-	} else {
-		if o.PolicyFile != "" {
-			return fmt.Errorf("feature '%s' must be enabled to set an audit policy", features.AdvancedAuditing)
-		}
-	}
-
-	// TODO: Generalize for alternative audit backends.
-	if len(o.Path) == 0 {
+func (o *AuditLogOptions) applyTo(c *server.Config) error {
+	if o.Path == "" {
 		return nil
 	}
 
@@ -89,6 +148,35 @@ func (o *AuditLogOptions) ApplyTo(c *server.Config) error {
 		}
 	}
 	c.LegacyAuditWriter = w
-	c.AuditBackend = pluginlog.NewBackend(w)
+
+	if advancedAuditingEnabled() {
+		c.AuditBackend = appendBackend(c.AuditBackend, pluginlog.NewBackend(w))
+	}
+	return nil
+}
+
+func (o *AuditWebhookOptions) AddFlags(fs *pflag.FlagSet) {
+	fs.StringVar(&o.ConfigFile, "audit-webhook-config-file", o.ConfigFile,
+		"Path to a kubeconfig formatted file that defines the audit webhook configuration."+
+			" Requires the 'AdvancedAuditing' feature gate.")
+	fs.StringVar(&o.Mode, "audit-webhook-mode", o.Mode,
+		"Strategy for sending audit events. Blocking indicates sending events should block"+
+			" server responses. Batch causes the webhook to buffer and send events"+
+			" asynchronously. Known modes are "+strings.Join(pluginwebhook.AllowedModes, ",")+".")
+}
+
+func (o *AuditWebhookOptions) applyTo(c *server.Config) error {
+	if o.ConfigFile == "" {
+		return nil
+	}
+
+	if !advancedAuditingEnabled() {
+		return fmt.Errorf("feature '%s' must be enabled to set an audit webhook", features.AdvancedAuditing)
+	}
+	webhook, err := pluginwebhook.NewBackend(o.ConfigFile, o.Mode)
+	if err != nil {
+		return fmt.Errorf("initializing audit webhook: %v", err)
+	}
+	c.AuditBackend = appendBackend(c.AuditBackend, webhook)
 	return nil
 }

staging/src/k8s.io/apiserver/pkg/server/options/recommended.go

@@ -31,7 +31,7 @@ type RecommendedOptions struct {
 	SecureServing  *SecureServingOptions
 	Authentication *DelegatingAuthenticationOptions
 	Authorization  *DelegatingAuthorizationOptions
-	Audit          *AuditLogOptions
+	Audit          *AuditOptions
 	Features       *FeatureOptions
 }
 
@@ -41,7 +41,7 @@ func NewRecommendedOptions(prefix string, copier runtime.ObjectCopier, codec run
 		SecureServing:  NewSecureServingOptions(),
 		Authentication: NewDelegatingAuthenticationOptions(),
 		Authorization:  NewDelegatingAuthorizationOptions(),
-		Audit:          NewAuditLogOptions(),
+		Audit:          NewAuditOptions(),
 		Features:       NewFeatureOptions(),
 	}
 }

staging/src/k8s.io/apiserver/plugin/pkg/audit/webhook/BUILD

@@ -0,0 +1,46 @@
+package(default_visibility = ["//visibility:public"])
+
+licenses(["notice"])
+
+load(
+    "@io_bazel_rules_go//go:def.bzl",
+    "go_library",
+    "go_test",
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = ["webhook_test.go"],
+    library = ":go_default_library",
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/github.com/stretchr/testify/assert:go_default_library",
+        "//vendor/github.com/stretchr/testify/require:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime/serializer/json:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit/v1alpha1:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/audit:go_default_library",
+        "//vendor/k8s.io/client-go/tools/clientcmd/api/v1:go_default_library",
+    ],
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = ["webhook.go"],
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/github.com/golang/glog:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apimachinery/announced:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apimachinery/registered:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/conversion:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/runtime:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit/install:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/apis/audit/v1alpha1:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/audit:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/util/webhook:go_default_library",
+    ],
+)

staging/src/k8s.io/apiserver/plugin/pkg/audit/webhook/webhook.go

@@ -0,0 +1,285 @@
+/*
+Copyright 2017 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 webhook implements the audit.Backend interface using HTTP webhooks.
+package webhook
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"time"
+
+	"github.com/golang/glog"
+
+	"k8s.io/apimachinery/pkg/apimachinery/announced"
+	"k8s.io/apimachinery/pkg/apimachinery/registered"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/conversion"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/util/runtime"
+	auditinternal "k8s.io/apiserver/pkg/apis/audit"
+	"k8s.io/apiserver/pkg/apis/audit/install"
+	auditv1alpha1 "k8s.io/apiserver/pkg/apis/audit/v1alpha1"
+	"k8s.io/apiserver/pkg/audit"
+	"k8s.io/apiserver/pkg/util/webhook"
+)
+
+const (
+	// ModeBatch indicates that the webhook should buffer audit events
+	// internally, sending batch updates either once a certain number of
+	// events have been received or a certain amount of time has passed.
+	ModeBatch = "batch"
+	// ModeBlocking causes the webhook to block on every attempt to process
+	// a set of events. This causes requests to the API server to wait for a
+	// round trip to the external audit service before sending a response.
+	ModeBlocking = "blocking"
+)
+
+// AllowedModes is the modes known by this webhook.
+var AllowedModes = []string{
+	ModeBatch,
+	ModeBlocking,
+}
+
+const (
+	// Default configuration values for ModeBatch.
+	//
+	// TODO(ericchiang): Make these value configurable. Maybe through a
+	// kubeconfig extension?
+	defaultBatchBufferSize = 1000        // Buffer up to 1000 events before blocking.
+	defaultBatchMaxSize    = 100         // Only send 100 events at a time.
+	defaultBatchMaxWait    = time.Minute // Send events at least once a minute.
+)
+
+// NewBackend returns an audit backend that sends events over HTTP to an external service.
+// The mode indicates the caching behavior of the webhook. Either blocking (ModeBlocking)
+// or buffered with batch POSTs (ModeBatch).
+func NewBackend(kubeConfigFile string, mode string) (audit.Backend, error) {
+	switch mode {
+	case ModeBatch:
+		return newBatchWebhook(kubeConfigFile)
+	case ModeBlocking:
+		return newBlockingWebhook(kubeConfigFile)
+	default:
+		return nil, fmt.Errorf("webhook mode %q is not in list of known modes (%s)",
+			mode, strings.Join(AllowedModes, ","))
+	}
+}
+
+var (
+	// NOTE: Copied from other webhook implementations
+	//
+	// Can we make these passable to NewGenericWebhook?
+	groupFactoryRegistry = make(announced.APIGroupFactoryRegistry)
+	groupVersions        = []schema.GroupVersion{auditv1alpha1.SchemeGroupVersion}
+	registry             = registered.NewOrDie("")
+)
+
+func init() {
+	registry.RegisterVersions(groupVersions)
+	if err := registry.EnableVersions(groupVersions...); err != nil {
+		panic(fmt.Sprintf("failed to enable version %v", groupVersions))
+	}
+	install.Install(groupFactoryRegistry, registry, audit.Scheme)
+}
+
+func loadWebhook(configFile string) (*webhook.GenericWebhook, error) {
+	return webhook.NewGenericWebhook(registry, audit.Codecs, configFile, groupVersions, 0)
+}
+
+func newBlockingWebhook(configFile string) (*blockingBackend, error) {
+	w, err := loadWebhook(configFile)
+	if err != nil {
+		return nil, err
+	}
+	return &blockingBackend{w}, nil
+}
+
+type blockingBackend struct {
+	w *webhook.GenericWebhook
+}
+
+func (b *blockingBackend) Run(stopCh <-chan struct{}) error {
+	return nil
+}
+
+func (b *blockingBackend) ProcessEvents(ev ...*auditinternal.Event) {
+	if err := b.processEvents(ev...); err != nil {
+		glog.Errorf("failed to POST webhook events: %v", err)
+	}
+}
+
+func (b *blockingBackend) processEvents(ev ...*auditinternal.Event) error {
+	var list auditinternal.EventList
+	for _, e := range ev {
+		list.Items = append(list.Items, *e)
+	}
+	// NOTE: No exponential backoff because this is the blocking webhook
+	// mode. Any attempts to retry will block API server requests.
+	return b.w.RestClient.Post().Body(&list).Do().Error()
+}
+
+// Copied from generated code in k8s.io/apiserver/pkg/apis/audit.
+//
+// TODO(ericchiang): Have the generated code expose these methods like metav1.GetGeneratedDeepCopyFuncs().
+var auditDeepCopyFuncs = []conversion.GeneratedDeepCopyFunc{
+	{Fn: auditinternal.DeepCopy_audit_Event, InType: reflect.TypeOf(&auditinternal.Event{})},
+	{Fn: auditinternal.DeepCopy_audit_EventList, InType: reflect.TypeOf(&auditinternal.EventList{})},
+	{Fn: auditinternal.DeepCopy_audit_GroupResources, InType: reflect.TypeOf(&auditinternal.GroupResources{})},
+	{Fn: auditinternal.DeepCopy_audit_ObjectReference, InType: reflect.TypeOf(&auditinternal.ObjectReference{})},
+	{Fn: auditinternal.DeepCopy_audit_Policy, InType: reflect.TypeOf(&auditinternal.Policy{})},
+	{Fn: auditinternal.DeepCopy_audit_PolicyList, InType: reflect.TypeOf(&auditinternal.PolicyList{})},
+	{Fn: auditinternal.DeepCopy_audit_PolicyRule, InType: reflect.TypeOf(&auditinternal.PolicyRule{})},
+	{Fn: auditinternal.DeepCopy_audit_UserInfo, InType: reflect.TypeOf(&auditinternal.UserInfo{})},
+}
+
+func newBatchWebhook(configFile string) (*batchBackend, error) {
+	w, err := loadWebhook(configFile)
+	if err != nil {
+		return nil, err
+	}
+
+	c := conversion.NewCloner()
+	for _, f := range metav1.GetGeneratedDeepCopyFuncs() {
+		if err := c.RegisterGeneratedDeepCopyFunc(f); err != nil {
+			return nil, fmt.Errorf("registering meta deep copy method: %v", err)
+		}
+	}
+
+	for _, f := range auditDeepCopyFuncs {
+		if err := c.RegisterGeneratedDeepCopyFunc(f); err != nil {
+			return nil, fmt.Errorf("registering audit deep copy method: %v", err)
+		}
+	}
+
+	return &batchBackend{
+		w:            w,
+		buffer:       make(chan *auditinternal.Event, defaultBatchBufferSize),
+		maxBatchSize: defaultBatchMaxSize,
+		maxBatchWait: defaultBatchMaxWait,
+		cloner:       c,
+	}, nil
+}
+
+type batchBackend struct {
+	w *webhook.GenericWebhook
+
+	// Cloner is used to deep copy events as they are buffered.
+	cloner *conversion.Cloner
+
+	// Channel to buffer events in memory before sending them on the webhook.
+	buffer chan *auditinternal.Event
+	// Maximum number of events that can be sent at once.
+	maxBatchSize int
+	// Amount of time to wait after sending events before force sending another set.
+	//
+	// Receiving maxBatchSize events will always trigger a send, regardless of
+	// if this amount of time has been reached.
+	maxBatchWait time.Duration
+}
+
+func (b *batchBackend) Run(stopCh <-chan struct{}) error {
+	f := func() {
+		// Recover from any panics caused by this method so a panic in the
+		// goroutine can't bring down the main routine.
+		defer runtime.HandleCrash()
+
+		t := time.NewTimer(b.maxBatchWait)
+		defer t.Stop() // Release ticker resources
+
+		b.sendBatchEvents(stopCh, t.C)
+	}
+
+	go func() {
+		for {
+			f()
+
+			select {
+			case <-stopCh:
+				return
+			default:
+			}
+		}
+	}()
+	return nil
+}
+
+// sendBatchEvents attempts to batch some number of events to the backend. It POSTs events
+// in a goroutine and logging any error encountered during the POST.
+//
+// The following things can cause sendBatchEvents to exit:
+//
+//   * Some maximum number of events are received.
+//   * Timer has passed, all queued events are sent.
+//   * StopCh is closed, all queued events are sent.
+//
+func (b *batchBackend) sendBatchEvents(stopCh <-chan struct{}, timer <-chan time.Time) {
+	var events []auditinternal.Event
+
+L:
+	for i := 0; i < b.maxBatchSize; i++ {
+		select {
+		case ev := <-b.buffer:
+			events = append(events, *ev)
+		case <-timer:
+			// Timer has expired. Send whatever events are in the queue.
+			break L
+		case <-stopCh:
+			// Webhook has shut down. Send the last events.
+			break L
+		}
+	}
+
+	if len(events) == 0 {
+		return
+	}
+
+	list := auditinternal.EventList{Items: events}
+	go func() {
+		// Execute the webhook POST in a goroutine to keep it from blocking.
+		// This lets the webhook continue to drain the queue immediatly.
+
+		defer runtime.HandleCrash()
+
+		err := webhook.WithExponentialBackoff(0, func() error {
+			return b.w.RestClient.Post().Body(&list).Do().Error()
+		})
+		if err != nil {
+			glog.Errorf("failed to POST webhook events: %v", err)
+		}
+	}()
+	return
+}
+
+func (b *batchBackend) ProcessEvents(ev ...*auditinternal.Event) {
+	for i, e := range ev {
+		// Per the audit.Backend interface these events are reused after being
+		// sent to the Sink. Deep copy and send the copy to the queue.
+		event := new(auditinternal.Event)
+		if err := auditinternal.DeepCopy_audit_Event(e, event, b.cloner); err != nil {
+			glog.Errorf("failed to clone audit event: %v: %#v", err, e)
+			return
+		}
+
+		select {
+		case b.buffer <- event:
+		default:
+			glog.Errorf("audit webhook queue blocked, failed to send %d event(s)", len(ev)-i)
+			return
+		}
+	}
+}

staging/src/k8s.io/apiserver/plugin/pkg/audit/webhook/webhook_test.go

@@ -0,0 +1,332 @@
+/*
+Copyright 2017 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 webhook
+
+import (
+	stdjson "encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/serializer/json"
+	auditinternal "k8s.io/apiserver/pkg/apis/audit"
+	auditv1alpha1 "k8s.io/apiserver/pkg/apis/audit/v1alpha1"
+	"k8s.io/apiserver/pkg/audit"
+	"k8s.io/client-go/tools/clientcmd/api/v1"
+)
+
+// newWebhookHandler returns a handler which recieves webhook events and decodes the
+// request body. The caller passes a callback which is called on each webhook POST.
+func newWebhookHandler(t *testing.T, cb func(events *auditv1alpha1.EventList)) http.Handler {
+	s := json.NewSerializer(json.DefaultMetaFactory, audit.Scheme, audit.Scheme, false)
+	return &testWebhookHandler{
+		t:          t,
+		onEvents:   cb,
+		serializer: s,
+	}
+}
+
+type testWebhookHandler struct {
+	t *testing.T
+
+	onEvents func(events *auditv1alpha1.EventList)
+
+	serializer runtime.Serializer
+}
+
+func (t *testWebhookHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	err := func() error {
+		body, err := ioutil.ReadAll(r.Body)
+		if err != nil {
+			return fmt.Errorf("read webhook request body: %v", err)
+		}
+
+		obj, _, err := t.serializer.Decode(body, nil, &auditv1alpha1.EventList{})
+		if err != nil {
+			return fmt.Errorf("decode request body: %v", err)
+		}
+		list, ok := obj.(*auditv1alpha1.EventList)
+		if !ok {
+			return fmt.Errorf("expected *v1alpha1.EventList got %T", obj)
+		}
+		t.onEvents(list)
+		return nil
+	}()
+
+	if err == nil {
+		io.WriteString(w, "{}")
+		return
+	}
+	// In a goroutine, can't call Fatal.
+	assert.NoError(t.t, err, "failed to read request body")
+	http.Error(w, err.Error(), http.StatusInternalServerError)
+}
+
+func newTestBlockingWebhook(t *testing.T, endpoint string) *blockingBackend {
+	return newWebhook(t, endpoint, ModeBlocking).(*blockingBackend)
+}
+
+func newTestBatchWebhook(t *testing.T, endpoint string) *batchBackend {
+	return newWebhook(t, endpoint, ModeBatch).(*batchBackend)
+}
+
+func newWebhook(t *testing.T, endpoint string, mode string) audit.Backend {
+	config := v1.Config{
+		Clusters: []v1.NamedCluster{
+			{Cluster: v1.Cluster{Server: endpoint, InsecureSkipTLSVerify: true}},
+		},
+	}
+	f, err := ioutil.TempFile("", "k8s_audit_webhook_test_")
+	require.NoError(t, err, "creating temp file")
+
+	defer func() {
+		f.Close()
+		os.Remove(f.Name())
+	}()
+
+	// NOTE(ericchiang): Do we need to use a proper serializer?
+	require.NoError(t, stdjson.NewEncoder(f).Encode(config), "writing kubeconfig")
+
+	backend, err := NewBackend(f.Name(), mode)
+	require.NoError(t, err, "initializing backend")
+
+	return backend
+}
+
+func TestWebhook(t *testing.T) {
+	gotEvents := false
+	defer func() { require.True(t, gotEvents, "no events received") }()
+
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		gotEvents = true
+	}))
+	defer s.Close()
+
+	backend := newTestBlockingWebhook(t, s.URL)
+
+	// Ensure this doesn't return a serialization error.
+	event := &auditinternal.Event{}
+	require.NoError(t, backend.processEvents(event), "failed to send events")
+}
+
+// waitForEmptyBuffer indicates when the sendBatchEvents method has read from the
+// existing buffer. This lets test coordinate closing a timer and stop channel
+// until the for loop has read from the buffer.
+func waitForEmptyBuffer(b *batchBackend) {
+	for len(b.buffer) != 0 {
+		time.Sleep(time.Millisecond)
+	}
+}
+
+func TestBatchWebhookMaxEvents(t *testing.T) {
+	nRest := 10
+	events := make([]*auditinternal.Event, defaultBatchMaxSize+nRest) // greater than max size.
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+
+	got := make(chan int, 2)
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		got <- len(events.Items)
+	}))
+	defer s.Close()
+
+	backend := newTestBatchWebhook(t, s.URL)
+
+	backend.ProcessEvents(events...)
+
+	stopCh := make(chan struct{})
+	timer := make(chan time.Time, 1)
+
+	backend.sendBatchEvents(stopCh, timer)
+	require.Equal(t, defaultBatchMaxSize, <-got, "did not get batch max size")
+
+	go func() {
+		waitForEmptyBuffer(backend) // wait for the buffer to empty
+		timer <- time.Now()         // Trigger the wait timeout
+	}()
+
+	backend.sendBatchEvents(stopCh, timer)
+	require.Equal(t, nRest, <-got, "failed to get the rest of the events")
+}
+
+func TestBatchWebhookStopCh(t *testing.T) {
+	events := make([]*auditinternal.Event, 1) // less than max size.
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+
+	expected := len(events)
+	got := make(chan int, 2)
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		got <- len(events.Items)
+	}))
+	defer s.Close()
+
+	backend := newTestBatchWebhook(t, s.URL)
+	backend.ProcessEvents(events...)
+
+	stopCh := make(chan struct{})
+	timer := make(chan time.Time)
+
+	go func() {
+		waitForEmptyBuffer(backend)
+		close(stopCh) // stop channel has stopped
+	}()
+	backend.sendBatchEvents(stopCh, timer)
+	require.Equal(t, expected, <-got, "get queued events after timer expires")
+}
+
+func TestBatchWebhookEmptyBuffer(t *testing.T) {
+	events := make([]*auditinternal.Event, 1) // less than max size.
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+
+	expected := len(events)
+	got := make(chan int, 2)
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		got <- len(events.Items)
+	}))
+	defer s.Close()
+
+	backend := newTestBatchWebhook(t, s.URL)
+
+	stopCh := make(chan struct{})
+	timer := make(chan time.Time, 1)
+
+	timer <- time.Now() // Timer is done.
+
+	// Buffer is empty, no events have been queued. This should exit but send no events.
+	backend.sendBatchEvents(stopCh, timer)
+
+	// Send additional events after the sendBatchEvents has been called.
+	backend.ProcessEvents(events...)
+	go func() {
+		waitForEmptyBuffer(backend)
+		timer <- time.Now()
+	}()
+
+	backend.sendBatchEvents(stopCh, timer)
+
+	// Make sure we didn't get a POST with zero events.
+	require.Equal(t, expected, <-got, "expected one event")
+}
+
+func TestBatchBufferFull(t *testing.T) {
+	events := make([]*auditinternal.Event, defaultBatchBufferSize+1) // More than buffered size
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		// Do nothing.
+	}))
+	defer s.Close()
+
+	backend := newTestBatchWebhook(t, s.URL)
+
+	// Make sure this doesn't block.
+	backend.ProcessEvents(events...)
+}
+
+func TestBatchRun(t *testing.T) {
+
+	// Divisable by max batch size so we don't have to wait for a minute for
+	// the test to finish.
+	events := make([]*auditinternal.Event, defaultBatchMaxSize*3)
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+
+	got := new(int64)
+	want := len(events)
+
+	wg := new(sync.WaitGroup)
+	wg.Add(want)
+	done := make(chan struct{})
+
+	go func() {
+		wg.Wait()
+		// When the expected number of events have been received, close the channel.
+		close(done)
+	}()
+
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		atomic.AddInt64(got, int64(len(events.Items)))
+		wg.Add(-len(events.Items))
+	}))
+	defer s.Close()
+
+	stopCh := make(chan struct{})
+	defer close(stopCh)
+
+	backend := newTestBatchWebhook(t, s.URL)
+
+	// Test the Run codepath. E.g. that the spawned goroutines behave correctly.
+	backend.Run(stopCh)
+
+	backend.ProcessEvents(events...)
+
+	select {
+	case <-done:
+		// Received all the events.
+	case <-time.After(2 * time.Minute):
+		t.Errorf("expected %d events got %d", want, atomic.LoadInt64(got))
+	}
+}
+
+func TestBatchConcurrentRequests(t *testing.T) {
+	events := make([]*auditinternal.Event, defaultBatchBufferSize) // Don't drop events
+	for i := range events {
+		events[i] = &auditinternal.Event{}
+	}
+
+	wg := new(sync.WaitGroup)
+	wg.Add(len(events))
+
+	s := httptest.NewServer(newWebhookHandler(t, func(events *auditv1alpha1.EventList) {
+		wg.Add(-len(events.Items))
+
+		// Since the webhook makes concurrent requests, blocking on the webhook response
+		// shouldn't block the webhook from sending more events.
+		//
+		// Wait for all responses to be received before sending the response.
+		wg.Wait()
+	}))
+	defer s.Close()
+
+	stopCh := make(chan struct{})
+	defer close(stopCh)
+
+	backend := newTestBatchWebhook(t, s.URL)
+	backend.Run(stopCh)
+
+	backend.ProcessEvents(events...)
+	// Wait for the webhook to receive all events.
+	wg.Wait()
+}

staging/src/k8s.io/kube-apiextensions-server/test/integration/testserver/start.go

@@ -42,7 +42,7 @@ func DefaultServerConfig() (*extensionsapiserver.Config, error) {
 	}
 
 	options := server.NewCustomResourceDefinitionsServerOptions(os.Stdout, os.Stderr)
-	options.RecommendedOptions.Audit.Path = "-"
+	options.RecommendedOptions.Audit.LogOptions.Path = "-"
 	options.RecommendedOptions.SecureServing.BindPort = port
 	options.RecommendedOptions.Authentication.SkipInClusterLookup = true
 	options.RecommendedOptions.SecureServing.BindAddress = net.ParseIP("127.0.0.1")