Add generic config info custom collector

Signed-off-by: Anish Ramasekar <anish.ramasekar@gmail.com>

staging/src/k8s.io/apiserver/pkg/util/configmetrics/info_collector.go

@@ -0,0 +1,92 @@
+/*
+Copyright 2025 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 configmetrics
+
+import (
+	"slices"
+	"sync/atomic"
+
+	"k8s.io/component-base/metrics"
+	"k8s.io/utils/ptr"
+)
+
+// HashProvider is an interface for getting the current config hash values
+type HashProvider interface {
+	GetCurrentHashes() []string
+	SetHashes(hashes ...string)
+}
+
+// AtomicHashProvider implements HashProvider using a single atomic pointer to a slice
+type AtomicHashProvider struct {
+	hashes *atomic.Pointer[[]string]
+}
+
+// NewAtomicHashProvider creates a new atomic hash provider
+func NewAtomicHashProvider() *AtomicHashProvider {
+	p := &AtomicHashProvider{
+		hashes: &atomic.Pointer[[]string]{},
+	}
+	// Initialize with empty slice
+	p.hashes.Store(ptr.To([]string{}))
+	return p
+}
+
+func (h *AtomicHashProvider) GetCurrentHashes() []string {
+	hashesPtr := h.hashes.Load()
+	if hashesPtr == nil {
+		// should never happen, but just in case
+		return []string{}
+	}
+	// Return a copy to prevent external modification
+	hashes := *hashesPtr
+	return slices.Clone(hashes)
+}
+
+func (h *AtomicHashProvider) SetHashes(hashes ...string) {
+	hashCopy := slices.Clone(hashes)
+	h.hashes.Store(&hashCopy)
+}
+
+// NewConfigInfoCustomCollector creates a custom collector for config hash info metrics.
+// This eliminates the need for state management and locks by collecting metrics on demand.
+func NewConfigInfoCustomCollector(desc *metrics.Desc, hashProvider HashProvider) metrics.StableCollector {
+	return &configInfoCustomCollector{
+		desc:         desc,
+		hashProvider: hashProvider,
+	}
+}
+
+type configInfoCustomCollector struct {
+	metrics.BaseStableCollector
+	desc         *metrics.Desc
+	hashProvider HashProvider
+}
+
+var _ metrics.StableCollector = &configInfoCustomCollector{}
+
+func (c *configInfoCustomCollector) DescribeWithStability(ch chan<- *metrics.Desc) {
+	ch <- c.desc
+}
+
+func (c *configInfoCustomCollector) CollectWithStability(ch chan<- metrics.Metric) {
+	hashes := c.hashProvider.GetCurrentHashes()
+	if len(hashes) == 0 {
+		return
+	}
+
+	ch <- metrics.NewLazyConstMetric(c.desc, metrics.GaugeValue, 1, hashes...)
+}

staging/src/k8s.io/apiserver/pkg/util/configmetrics/info_collector_test.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2025 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 configmetrics
+
+import (
+	"testing"
+)
+
+// assertHashesEqual is a test helper that compares expected and actual hash slices
+func assertHashesEqual(t *testing.T, expected, actual []string) {
+	t.Helper()
+	if len(actual) != len(expected) {
+		t.Errorf("expected %d hashes, got %d", len(expected), len(actual))
+		return
+	}
+	for i, hash := range actual {
+		if hash != expected[i] {
+			t.Errorf("expected hash %q at index %d, got %q", expected[i], i, hash)
+		}
+	}
+}
+
+func TestAtomicHashProvider(t *testing.T) {
+	provider := NewAtomicHashProvider()
+
+	apiServerIDHash := "sha256:abc123"
+	configHash := "sha256:hash1"
+
+	// Test initial state
+	hashes := provider.GetCurrentHashes()
+	assertHashesEqual(t, []string{}, hashes)
+
+	// Test setting hashes
+	provider.SetHashes(apiServerIDHash, configHash)
+	hashes = provider.GetCurrentHashes()
+	assertHashesEqual(t, []string{apiServerIDHash, configHash}, hashes)
+
+	// Test updating hashes
+	newConfigHash := "sha256:hash2"
+	provider.SetHashes(apiServerIDHash, newConfigHash)
+	hashes = provider.GetCurrentHashes()
+	assertHashesEqual(t, []string{apiServerIDHash, newConfigHash}, hashes)
+
+	// Test empty hashes
+	provider.SetHashes()
+	hashes = provider.GetCurrentHashes()
+	assertHashesEqual(t, []string{}, hashes)
+}