custom retry strategy in GenericWebhook

Kubernetes-commit: 4877b0b7b50bdc3eaaadd3f968fd846c1396b708

pkg/util/webhook/webhook.go

@@ -36,9 +36,28 @@ import (
 // timeout of the HTTP request, including reading the response body.
 const defaultRequestTimeout = 30 * time.Second
 
+// GenericWebhook defines a generic client for webhooks with commonly used capabilities,
+// such as retry requests.
 type GenericWebhook struct {
 	RestClient     *rest.RESTClient
 	InitialBackoff time.Duration
+	ShouldRetry    func(error) bool
+}
+
+// DefaultShouldRetry is a default implementation for the GenericWebhook ShouldRetry function property.
+// If the error reason is one of: networking (connection reset) or http (InternalServerError (500), GatewayTimeout (504), TooManyRequests (429)),
+// or apierrors.SuggestsClientDelay() returns true, then the function advises a retry.
+// Otherwise it returns false for an immediate fail.
+func DefaultShouldRetry(err error) bool {
+	// these errors indicate a transient error that should be retried.
+	if net.IsConnectionReset(err) || apierrors.IsInternalError(err) || apierrors.IsTimeout(err) || apierrors.IsTooManyRequests(err) {
+		return true
+	}
+	// if the error sends the Retry-After header, we respect it as an explicit confirmation we should retry.
+	if _, shouldRetry := apierrors.SuggestsClientDelay(err); shouldRetry {
+		return true
+	}
+	return false
 }
 
 // NewGenericWebhook creates a new GenericWebhook from the provided kubeconfig file.
@@ -77,23 +96,28 @@ func newGenericWebhook(scheme *runtime.Scheme, codecFactory serializer.CodecFact
 		return nil, err
 	}
 
-	return &GenericWebhook{restClient, initialBackoff}, nil
+	return &GenericWebhook{restClient, initialBackoff, DefaultShouldRetry}, nil
 }
 
 // WithExponentialBackoff will retry webhookFn() up to 5 times with exponentially increasing backoff when
-// it returns an error for which apierrors.SuggestsClientDelay() or apierrors.IsInternalError() returns true.
+// it returns an error for which this GenericWebhook's ShouldRetry function returns true, confirming it to
+// be retriable. If no ShouldRetry has been defined for the webhook, then the default one is used (DefaultShouldRetry).
 func (g *GenericWebhook) WithExponentialBackoff(ctx context.Context, webhookFn func() rest.Result) rest.Result {
 	var result rest.Result
+	shouldRetry := g.ShouldRetry
+	if shouldRetry == nil {
+		shouldRetry = DefaultShouldRetry
+	}
 	WithExponentialBackoff(ctx, g.InitialBackoff, func() error {
 		result = webhookFn()
 		return result.Error()
-	})
+	}, shouldRetry)
 	return result
 }
 
-// WithExponentialBackoff will retry webhookFn() up to 5 times with exponentially increasing backoff when
-// it returns an error for which apierrors.SuggestsClientDelay() or apierrors.IsInternalError() returns true.
-func WithExponentialBackoff(ctx context.Context, initialBackoff time.Duration, webhookFn func() error) error {
+// WithExponentialBackoff will retry webhookFn up to 5 times with exponentially increasing backoff when
+// it returns an error for which shouldRetry returns true, confirming it to be retriable.
+func WithExponentialBackoff(ctx context.Context, initialBackoff time.Duration, webhookFn func() error, shouldRetry func(error) bool) error {
 	backoff := wait.Backoff{
 		Duration: initialBackoff,
 		Factor:   1.5,
@@ -104,18 +128,11 @@ func WithExponentialBackoff(ctx context.Context, initialBackoff time.Duration, w
 	var err error
 	wait.ExponentialBackoff(backoff, func() (bool, error) {
 		err = webhookFn()
-
 		if ctx.Err() != nil {
 			// we timed out or were cancelled, we should not retry
 			return true, err
 		}
-
-		// these errors indicate a transient error that should be retried.
-		if net.IsConnectionReset(err) || apierrors.IsInternalError(err) || apierrors.IsTimeout(err) || apierrors.IsTooManyRequests(err) {
-			return false, nil
-		}
-		// if the error sends the Retry-After header, we respect it as an explicit confirmation we should retry.
-		if _, shouldRetry := apierrors.SuggestsClientDelay(err); shouldRetry {
+		if shouldRetry(err) {
 			return false, nil
 		}
 		if err != nil {

plugin/pkg/audit/webhook/webhook.go

@@ -44,9 +44,27 @@ func init() {
 	install.Install(audit.Scheme)
 }
 
+// retryOnError enforces the webhook client to retry requests
+// on error regardless of its nature.
+// The default implementation considers a very limited set of
+// 'retriable' errors, assuming correct use of HTTP codes by
+// external webhooks.
+// That may easily lead to dropped audit events. In fact, there is
+// hardly any error that could be a justified reason NOT to retry
+// sending audit events if there is even a slight chance that the
+// receiving service gets back to normal at some point.
+func retryOnError(err error) bool {
+	if err != nil {
+		return true
+	}
+	return false
+}
+
 func loadWebhook(configFile string, groupVersion schema.GroupVersion, initialBackoff time.Duration) (*webhook.GenericWebhook, error) {
-	return webhook.NewGenericWebhook(audit.Scheme, audit.Codecs, configFile,
+	w, err := webhook.NewGenericWebhook(audit.Scheme, audit.Codecs, configFile,
 		[]schema.GroupVersion{groupVersion}, initialBackoff)
+	w.ShouldRetry = retryOnError
+	return w, err
 }
 
 type backend struct {
@@ -61,6 +79,7 @@ func NewDynamicBackend(rc *rest.RESTClient, initialBackoff time.Duration) audit.
 		w: &webhook.GenericWebhook{
 			RestClient:     rc,
 			InitialBackoff: initialBackoff,
+			ShouldRetry:    retryOnError,
 		},
 		name: fmt.Sprintf("dynamic_%s", PluginName),
 	}

plugin/pkg/authenticator/token/webhook/webhook.go

@@ -101,7 +101,7 @@ func (w *WebhookTokenAuthenticator) AuthenticateToken(ctx context.Context, token
 	webhook.WithExponentialBackoff(ctx, w.initialBackoff, func() error {
 		result, err = w.tokenReview.CreateContext(ctx, r)
 		return err
-	})
+	}, webhook.DefaultShouldRetry)
 	if err != nil {
 		// An error here indicates bad configuration or an outage. Log for debugging.
 		klog.Errorf("Failed to make webhook authenticator request: %v", err)

plugin/pkg/authorizer/webhook/webhook.go

@@ -191,7 +191,7 @@ func (w *WebhookAuthorizer) Authorize(ctx context.Context, attr authorizer.Attri
 		webhook.WithExponentialBackoff(ctx, w.initialBackoff, func() error {
 			result, err = w.subjectAccessReview.CreateContext(ctx, r)
 			return err
-		})
+		}, webhook.DefaultShouldRetry)
 		if err != nil {
 			// An error here indicates bad configuration or an outage. Log for debugging.
 			klog.Errorf("Failed to make webhook authorizer request: %v", err)