webhook: add options to disable resource_namespace tag in metrics (#2931

)

* webhook: add options to disable resource_namespace tag in metrics

To add some context, historically, `resource_name` was removed from this
tag list due to its high potential of causing high metrics cardinality.
See [#1464][1] for more information.

While that's great, but it might not be sufficient for large scale use
cases where namespaces can be super dynamic (with generateName, too) or
grows fase enough. There is an issue report from
[tektoncd/pipeline#3171][2] which talks about this.

This proposal makes it possible to disable `resource_namespace` tag via
an option function. The default behavior is not changed, so no user
impact if any of existing users rely on this tag. There is no API
contract change either due to the beauty of variadic functions.

Now downstream projects can consume this by override `StatsReporter` in
webhook context options with their own preference. As a caveat here, if
downstream project does choose to override `StatsReporter`, the default
`ReportMetrics` function shouldn't be called by default as they may now
have a different set of tag keys to report. As such, this function is
only called if the default `StatsReporter` is used.

[1]: #1464
[2]: tektoncd/pipeline#3171

* webhook: add StatsReporterOptions in webhook.Options

There are two ways to customize StatsReporter:

1. Use a whole new StatsReporter implementation.
1. Or pass Option funcs to customize the default StatsReporter.

Option 1 is less practical at this time due to the metrics registration
conflict. `webhook.RegisterMetrics()` is called regardless which
StatsReporter implementation is used (which is a problem by itself). The
second option is more practical since it works well without dealing with
metrics conflicts.

The `webhook.Option` in particular allows people to discard certain
metrics tags.

injection/sharedmain/main.go

@@ -290,7 +290,12 @@ func MainWithConfig(ctx context.Context, component string, cfg *rest.Config, cto
 	var wh *webhook.Webhook
 	if len(webhooks) > 0 {
 		// Register webhook metrics
-		webhook.RegisterMetrics()
+		opts := webhook.GetOptions(ctx)
+		if opts != nil {
+			webhook.RegisterMetrics(opts.StatsReporterOptions...)
+		} else {
+			webhook.RegisterMetrics()
+		}
 
 		wh, err = webhook.New(ctx, webhooks)
 		if err != nil {

webhook/stats_reporter.go

@@ -26,6 +26,7 @@ import (
 	"go.opencensus.io/tag"
 	admissionv1 "k8s.io/api/admission/v1"
 	apixv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"knative.dev/pkg/metrics"
 )
 
@@ -65,43 +66,128 @@ var (
 	resultCodeKey        = tag.MustNewKey("result_code")
 )
 
+type admissionToValue func(*admissionv1.AdmissionRequest, *admissionv1.AdmissionResponse) string
+type conversionToValue func(*apixv1.ConversionRequest, *apixv1.ConversionResponse) string
+
+var (
+	allAdmissionTags = map[tag.Key]admissionToValue{
+		requestOperationKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return string(req.Operation)
+		},
+		kindGroupKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Kind.Group
+		},
+		kindVersionKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Kind.Version
+		},
+		kindKindKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Kind.Kind
+		},
+		resourceGroupKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Resource.Group
+		},
+		resourceVersionKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Resource.Version
+		},
+		resourceResourceKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Resource.Resource
+		},
+		resourceNamespaceKey: func(req *admissionv1.AdmissionRequest, _ *admissionv1.AdmissionResponse) string {
+			return req.Namespace
+		},
+		admissionAllowedKey: func(_ *admissionv1.AdmissionRequest, resp *admissionv1.AdmissionResponse) string {
+			return strconv.FormatBool(resp.Allowed)
+		},
+	}
+	allConversionTags = map[tag.Key]conversionToValue{
+		desiredAPIVersionKey: func(req *apixv1.ConversionRequest, _ *apixv1.ConversionResponse) string {
+			return req.DesiredAPIVersion
+		},
+		resultStatusKey: func(_ *apixv1.ConversionRequest, resp *apixv1.ConversionResponse) string {
+			return resp.Result.Status
+		},
+		resultReasonKey: func(_ *apixv1.ConversionRequest, resp *apixv1.ConversionResponse) string {
+			return string(resp.Result.Reason)
+		},
+		resultCodeKey: func(_ *apixv1.ConversionRequest, resp *apixv1.ConversionResponse) string {
+			return strconv.Itoa(int(resp.Result.Code))
+		},
+	}
+)
+
 // StatsReporter reports webhook metrics
 type StatsReporter interface {
 	ReportAdmissionRequest(request *admissionv1.AdmissionRequest, response *admissionv1.AdmissionResponse, d time.Duration) error
 	ReportConversionRequest(request *apixv1.ConversionRequest, response *apixv1.ConversionResponse, d time.Duration) error
 }
 
+type statsReporterOptions struct {
+	tagsToExclude sets.Set[string]
+}
+
+type StatsReporterOption func(_ *statsReporterOptions)
+
+func WithoutTags(tags ...string) StatsReporterOption {
+	return func(opts *statsReporterOptions) {
+		opts.tagsToExclude.Insert(tags...)
+	}
+}
+
 // reporter implements StatsReporter interface
 type reporter struct {
 	ctx context.Context
+
+	admissionTags  map[tag.Key]admissionToValue
+	conversionTags map[tag.Key]conversionToValue
 }
 
 // NewStatsReporter creates a reporter for webhook metrics
-func NewStatsReporter() (StatsReporter, error) {
+func NewStatsReporter(opts ...StatsReporterOption) (StatsReporter, error) {
 	ctx, err := tag.New(
 		context.Background(),
 	)
 	if err != nil {
 		return nil, err
 	}
 
-	return &reporter{ctx: ctx}, nil
+	options := statsReporterOptions{
+		tagsToExclude: sets.New[string](),
+	}
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	admissionTags := make(map[tag.Key]admissionToValue)
+	for key, f := range allAdmissionTags {
+		if options.tagsToExclude.Has(key.Name()) {
+			continue
+		}
+		admissionTags[key] = f
+	}
+	conversionTags := make(map[tag.Key]conversionToValue)
+	for key, f := range allConversionTags {
+		if options.tagsToExclude.Has(key.Name()) {
+			continue
+		}
+		conversionTags[key] = f
+	}
+
+	return &reporter{
+		ctx:            ctx,
+		admissionTags:  admissionTags,
+		conversionTags: conversionTags,
+	}, nil
 }
 
 // Captures req count metric, recording the count and the duration
 func (r *reporter) ReportAdmissionRequest(req *admissionv1.AdmissionRequest, resp *admissionv1.AdmissionResponse, d time.Duration) error {
-	ctx, err := tag.New(
-		r.ctx,
-		tag.Insert(requestOperationKey, string(req.Operation)),
-		tag.Insert(kindGroupKey, req.Kind.Group),
-		tag.Insert(kindVersionKey, req.Kind.Version),
-		tag.Insert(kindKindKey, req.Kind.Kind),
-		tag.Insert(resourceGroupKey, req.Resource.Group),
-		tag.Insert(resourceVersionKey, req.Resource.Version),
-		tag.Insert(resourceResourceKey, req.Resource.Resource),
-		tag.Insert(resourceNamespaceKey, req.Namespace),
-		tag.Insert(admissionAllowedKey, strconv.FormatBool(resp.Allowed)),
-	)
+	mutators := make([]tag.Mutator, 0, len(r.admissionTags))
+
+	for key, f := range r.admissionTags {
+		mutators = append(mutators, tag.Insert(key, f(req, resp)))
+	}
+
+	ctx, err := tag.New(r.ctx, mutators...)
 	if err != nil {
 		return err
 	}
@@ -114,13 +200,13 @@ func (r *reporter) ReportAdmissionRequest(req *admissionv1.AdmissionRequest, res
 
 // Captures req count metric, recording the count and the duration
 func (r *reporter) ReportConversionRequest(req *apixv1.ConversionRequest, resp *apixv1.ConversionResponse, d time.Duration) error {
-	ctx, err := tag.New(
-		r.ctx,
-		tag.Insert(desiredAPIVersionKey, req.DesiredAPIVersion),
-		tag.Insert(resultStatusKey, resp.Result.Status),
-		tag.Insert(resultReasonKey, string(resp.Result.Reason)),
-		tag.Insert(resultCodeKey, strconv.Itoa(int(resp.Result.Code))),
-	)
+	mutators := make([]tag.Mutator, 0, len(r.conversionTags))
+
+	for key, f := range r.conversionTags {
+		mutators = append(mutators, tag.Insert(key, f(req, resp)))
+	}
+
+	ctx, err := tag.New(r.ctx, mutators...)
 	if err != nil {
 		return err
 	}
@@ -131,21 +217,27 @@ func (r *reporter) ReportConversionRequest(req *apixv1.ConversionRequest, resp *
 	return nil
 }
 
-func RegisterMetrics() {
-	tagKeys := []tag.Key{
-		requestOperationKey,
-		kindGroupKey,
-		kindVersionKey,
-		kindKindKey,
-		resourceGroupKey,
-		resourceVersionKey,
-		resourceResourceKey,
-		resourceNamespaceKey,
-		admissionAllowedKey,
-		desiredAPIVersionKey,
-		resultStatusKey,
-		resultReasonKey,
-		resultCodeKey}
+func RegisterMetrics(opts ...StatsReporterOption) {
+	options := statsReporterOptions{
+		tagsToExclude: sets.New[string](),
+	}
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	tagKeys := []tag.Key{}
+	for tag := range allAdmissionTags {
+		if options.tagsToExclude.Has(tag.Name()) {
+			continue
+		}
+		tagKeys = append(tagKeys, tag)
+	}
+	for tag := range allConversionTags {
+		if options.tagsToExclude.Has(tag.Name()) {
+			continue
+		}
+		tagKeys = append(tagKeys, tag)
+	}
 
 	if err := view.Register(
 		&view.View{

webhook/stats_reporter_test.go

@@ -70,6 +70,47 @@ func TestWebhookStatsReporterAdmission(t *testing.T) {
 	metricstest.CheckDistributionData(t, requestLatenciesName, expectedTags, 2, shortTime, longTime)
 }
 
+func TestWebhookStatsReporterAdmissionWithoutNamespaceTag(t *testing.T) {
+	setup(WithoutTags(resourceNamespaceKey.Name()))
+	req := &admissionv1.AdmissionRequest{
+		UID:       "705ab4f5-6393-11e8-b7cc-42010a800002",
+		Kind:      metav1.GroupVersionKind{Group: "autoscaling", Version: "v1", Kind: "Scale"},
+		Resource:  metav1.GroupVersionResource{Group: "apps", Version: "v1", Resource: "deployments"},
+		Name:      "my-deployment",
+		Namespace: "my-namespace",
+		Operation: admissionv1.Update,
+	}
+
+	resp := &admissionv1.AdmissionResponse{
+		UID:     req.UID,
+		Allowed: true,
+	}
+
+	r, _ := NewStatsReporter(WithoutTags(resourceNamespaceKey.Name()))
+
+	shortTime, longTime := 1100.0, 9100.0
+	expectedTags := map[string]string{
+		requestOperationKey.Name(): string(req.Operation),
+		kindGroupKey.Name():        req.Kind.Group,
+		kindVersionKey.Name():      req.Kind.Version,
+		kindKindKey.Name():         req.Kind.Kind,
+		resourceGroupKey.Name():    req.Resource.Group,
+		resourceVersionKey.Name():  req.Resource.Version,
+		resourceResourceKey.Name(): req.Resource.Resource,
+		admissionAllowedKey.Name(): strconv.FormatBool(resp.Allowed),
+	}
+
+	if err := r.ReportAdmissionRequest(req, resp, time.Duration(shortTime)*time.Millisecond); err != nil {
+		t.Fatalf("ReportAdmissionRequest() = %v", err)
+	}
+	if err := r.ReportAdmissionRequest(req, resp, time.Duration(longTime)*time.Millisecond); err != nil {
+		t.Fatalf("ReportAdmissionRequest() = %v", err)
+	}
+
+	metricstest.CheckCountData(t, requestCountName, expectedTags, 2)
+	metricstest.CheckDistributionData(t, requestLatenciesName, expectedTags, 2, shortTime, longTime)
+}
+
 func TestWebhookStatsReporterConversion(t *testing.T) {
 	setup()
 	req := &apixv1.ConversionRequest{
@@ -103,12 +144,12 @@ func TestWebhookStatsReporterConversion(t *testing.T) {
 	metricstest.CheckDistributionData(t, requestLatenciesName, expectedTags, 2, shortTime, longTime)
 }
 
-func setup() {
-	resetMetrics()
+func setup(opts ...StatsReporterOption) {
+	resetMetrics(opts...)
 }
 
 // opencensus metrics carry global state that need to be reset between unit tests
-func resetMetrics() {
+func resetMetrics(opts ...StatsReporterOption) {
 	metricstest.Unregister(requestCountName, requestLatenciesName)
-	RegisterMetrics()
+	RegisterMetrics(opts...)
 }

webhook/webhook.go

@@ -70,6 +70,9 @@ type Options struct {
 	// only a single port for the service.
 	Port int
 
+	// StatsReporterOptions are the options used to initialize the default StatsReporter
+	StatsReporterOptions []StatsReporterOption
+
 	// StatsReporter reports metrics about the webhook.
 	// This will be automatically initialized by the constructor if left uninitialized.
 	StatsReporter StatsReporter
@@ -144,7 +147,7 @@ func New(
 	logger := logging.FromContext(ctx)
 
 	if opts.StatsReporter == nil {
-		reporter, err := NewStatsReporter()
+		reporter, err := NewStatsReporter(opts.StatsReporterOptions...)
 		if err != nil {
 			return nil, err
 		}