feat: add default implementation for providers

docs/getting-started.md

@@ -56,6 +56,7 @@ import (
     "k8s.io/metrics/pkg/apis/custom_metrics"
 
     "sigs.k8s.io/custom-metrics-apiserver/pkg/provider"
+    "sigs.k8s.io/custom-metrics-apiserver/pkg/provider/defaults"
     "sigs.k8s.io/custom-metrics-apiserver/pkg/provider/helpers"
 )
 ```
@@ -76,35 +77,14 @@ type CustomMetricsProvider interface {
 First, there's a method for listing all metrics available at any point in
 time.  It's used to populate the discovery information in the API, so that
 clients can know what metrics are available.  It's not allowed to fail (it
-doesn't return any error), and it should return quickly, so it's suggested
-that you update it asynchronously in real-world code.
+doesn't return any error), and it should return quickly. 
 
-For this walkthrough, you can just return a few statically-named metrics,
-two that are namespaced, and one that's on namespaces themselves, and thus
-root-scoped:
-
-```go
-func (p *yourProvider) ListAllMetrics() []provider.CustomMetricInfo {
-    return []provider.CustomMetricInfo{
-        // these are mostly arbitrary examples
-        {
-            GroupResource: schema.GroupResource{Group: "", Resource: "pods"},
-            Metric:        "packets-per-second",
-            Namespaced:    true,
-        },
-        {
-            GroupResource: schema.GroupResource{Group: "", Resource: "services"},
-            Metric:        "connections-per-second",
-            Namespaced:    true,
-        },
-        {
-            GroupResource: schema.GroupResource{Group: "", Resource: "namespaces"},
-            Metric:        "work-queue-length",
-            Namespaced:    false,
-        },
-    }
-}
-```
+You can list your metrics (asynchronously) and return them on every request.
+This is not mandatory because kubernetes can request metric values without 
+listing them before, but maybe there are some cases where is useful. To 
+provide a unified solution, a default implementation is provided thanks to
+`DefaultCustomMetricsProvider` (and `DefaultExternalMetricsProvider` for 
+external metrics)
 
 Next, you'll need to implement the methods that actually fetch the
 metrics. There are methods for fetching metrics describing arbitrary Kubernetes
@@ -189,6 +169,8 @@ already have sufficient information in your metrics pipeline:
 
 ```go
 type yourProvider struct {
+    defaults.DefaultCustomMetricsProvider
+    defaults.DefaultExternalMetricsProvider
     client dynamic.Interface
     mapper apimeta.RESTMapper
 

pkg/apiserver/installer/apiserver_test.go

@@ -45,6 +45,7 @@ import (
 	emv1beta1 "k8s.io/metrics/pkg/apis/external_metrics/v1beta1"
 
 	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider"
+	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider/defaults"
 	custommetricstorage "sigs.k8s.io/custom-metrics-apiserver/pkg/registry/custom_metrics"
 	externalmetricstorage "sigs.k8s.io/custom-metrics-apiserver/pkg/registry/external_metrics"
 	sampleprovider "sigs.k8s.io/custom-metrics-apiserver/test-adapter/provider"
@@ -179,7 +180,8 @@ type fakeCMProvider struct {
 	namespacedValues       map[string][]custom_metrics.MetricValue
 	rootSubsetCounts       map[string]int
 	namespacedSubsetCounts map[string]int
-	metrics                []provider.CustomMetricInfo
+
+	defaults.DefaultCustomMetricsProvider
 }
 
 func (p *fakeCMProvider) valuesFor(name types.NamespacedName, info provider.CustomMetricInfo) (string, []custom_metrics.MetricValue, bool) {
@@ -241,10 +243,6 @@ func (p *fakeCMProvider) GetMetricBySelector(_ context.Context, namespace string
 	return &trimmedValues, nil
 }
 
-func (p *fakeCMProvider) ListAllMetrics() []provider.CustomMetricInfo {
-	return p.metrics
-}
-
 type T struct {
 	Method        string
 	Path          string

pkg/provider/defaults/default_metric_providers.go

@@ -0,0 +1,42 @@
+/*
+Copyright 2023 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 defaults provides a default implementation of metrics providers.
+package defaults
+
+import (
+	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider"
+)
+
+type DefaultExternalMetricsProvider struct{}
+
+func (em DefaultExternalMetricsProvider) ListAllExternalMetrics() []provider.ExternalMetricInfo {
+	return []provider.ExternalMetricInfo{
+		{
+			Metric: "externalmetric",
+		},
+	}
+}
+
+type DefaultCustomMetricsProvider struct{}
+
+func (cm DefaultCustomMetricsProvider) ListAllMetrics() []provider.CustomMetricInfo {
+	return []provider.CustomMetricInfo{
+		{
+			Metric: "custommetric",
+		},
+	}
+}

pkg/provider/fake/fake.go

@@ -26,9 +26,13 @@ import (
 	"k8s.io/metrics/pkg/apis/external_metrics"
 
 	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider"
+	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider/defaults"
 )
 
-type fakeProvider struct{}
+type fakeProvider struct {
+	defaults.DefaultCustomMetricsProvider
+	defaults.DefaultExternalMetricsProvider
+}
 
 func (*fakeProvider) GetMetricByName(_ context.Context, _ types.NamespacedName, _ provider.CustomMetricInfo, _ labels.Selector) (*custom_metrics.MetricValue, error) {
 	return &custom_metrics.MetricValue{}, nil
@@ -38,18 +42,10 @@ func (*fakeProvider) GetMetricBySelector(_ context.Context, _ string, _ labels.S
 	return &custom_metrics.MetricValueList{}, nil
 }
 
-func (*fakeProvider) ListAllMetrics() []provider.CustomMetricInfo {
-	return []provider.CustomMetricInfo{}
-}
-
 func (*fakeProvider) GetExternalMetric(_ context.Context, _ string, _ labels.Selector, _ provider.ExternalMetricInfo) (*external_metrics.ExternalMetricValueList, error) {
 	return &external_metrics.ExternalMetricValueList{}, nil
 }
 
-func (*fakeProvider) ListAllExternalMetrics() []provider.ExternalMetricInfo {
-	return []provider.ExternalMetricInfo{}
-}
-
 // NewProvider creates a fake implementation of MetricsProvider.
 func NewProvider() provider.MetricsProvider {
 	return &fakeProvider{}

pkg/provider/interfaces.go

@@ -92,8 +92,8 @@ type CustomMetricsProvider interface {
 
 	// ListAllMetrics provides a list of all available metrics at
 	// the current time.  Note that this is not allowed to return
-	// an error, so it is recommended that implementors cache and
-	// periodically update this list, instead of querying every time.
+	// an error, so it is recommended that implementors use the
+	// default implementation provided by DefaultCustomMetricsProvider.
 	ListAllMetrics() []CustomMetricInfo
 }
 
@@ -104,6 +104,11 @@ type CustomMetricsProvider interface {
 type ExternalMetricsProvider interface {
 	GetExternalMetric(ctx context.Context, namespace string, metricSelector labels.Selector, info ExternalMetricInfo) (*external_metrics.ExternalMetricValueList, error)
 
+	// ListAllExternalMetrics provides a list of all available
+	// external metrics at the current time.
+	// Note that this is not allowed to return an error, so it is
+	// recommended that implementors use the default implementation
+	// provided by DefaultExternalMetricsProvider.
 	ListAllExternalMetrics() []ExternalMetricInfo
 }
 

test-adapter/provider/provider.go

@@ -35,6 +35,7 @@ import (
 	"k8s.io/metrics/pkg/apis/external_metrics"
 
 	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider"
+	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider/defaults"
 	"sigs.k8s.io/custom-metrics-apiserver/pkg/provider/helpers"
 )
 
@@ -105,6 +106,8 @@ var _ provider.MetricsProvider = &testingProvider{}
 
 // testingProvider is a sample implementation of provider.MetricsProvider which stores a map of fake metrics
 type testingProvider struct {
+	defaults.DefaultCustomMetricsProvider
+	defaults.DefaultExternalMetricsProvider
 	client dynamic.Interface
 	mapper apimeta.RESTMapper
 
@@ -308,25 +311,6 @@ func (p *testingProvider) GetMetricBySelector(_ context.Context, namespace strin
 	return p.metricsFor(namespace, selector, info, metricSelector)
 }
 
-func (p *testingProvider) ListAllMetrics() []provider.CustomMetricInfo {
-	p.valuesLock.RLock()
-	defer p.valuesLock.RUnlock()
-
-	// Get unique CustomMetricInfos from wrapper CustomMetricResources
-	infos := make(map[provider.CustomMetricInfo]struct{})
-	for resource := range p.values {
-		infos[resource.CustomMetricInfo] = struct{}{}
-	}
-
-	// Build slice of CustomMetricInfos to be returns
-	metrics := make([]provider.CustomMetricInfo, 0, len(infos))
-	for info := range infos {
-		metrics = append(metrics, info)
-	}
-
-	return metrics
-}
-
 func (p *testingProvider) GetExternalMetric(_ context.Context, _ string, metricSelector labels.Selector, info provider.ExternalMetricInfo) (*external_metrics.ExternalMetricValueList, error) {
 	p.valuesLock.RLock()
 	defer p.valuesLock.RUnlock()
@@ -344,14 +328,3 @@ func (p *testingProvider) GetExternalMetric(_ context.Context, _ string, metricS
 		Items: matchingMetrics,
 	}, nil
 }
-
-func (p *testingProvider) ListAllExternalMetrics() []provider.ExternalMetricInfo {
-	p.valuesLock.RLock()
-	defer p.valuesLock.RUnlock()
-
-	externalMetricsInfo := []provider.ExternalMetricInfo{}
-	for _, metric := range p.externalMetrics {
-		externalMetricsInfo = append(externalMetricsInfo, metric.info)
-	}
-	return externalMetricsInfo
-}