add sync_agent_published_resource metric

go.mod

@@ -25,6 +25,7 @@ require (
 	github.com/kcp-dev/sdk v0.31.0
 	github.com/kcp-dev/virtual-workspace-framework v0.31.0
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2
+	github.com/prometheus/client_golang v1.23.2
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/pflag v1.0.10
 	github.com/tidwall/gjson v1.18.0
@@ -95,7 +96,6 @@ require (
 	github.com/modern-go/reflect2 v1.0.3-0.20250322232337-35a7c28c31ee // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/onsi/gomega v1.39.1 // indirect
-	github.com/prometheus/client_golang v1.23.2 // indirect
 	github.com/prometheus/client_model v0.6.2 // indirect
 	github.com/prometheus/common v0.67.5 // indirect
 	github.com/prometheus/procfs v0.20.1 // indirect

internal/controller/apiexport/controller.go

@@ -26,6 +26,7 @@ import (
 	predicateutil "github.com/kcp-dev/api-syncagent/internal/controllerutil/predicate"
 	"github.com/kcp-dev/api-syncagent/internal/discovery"
 	"github.com/kcp-dev/api-syncagent/internal/kcp"
+	"github.com/kcp-dev/api-syncagent/internal/metrics"
 	"github.com/kcp-dev/api-syncagent/internal/projection"
 	"github.com/kcp-dev/api-syncagent/internal/resources/reconciling"
 	syncagentv1alpha1 "github.com/kcp-dev/api-syncagent/sdk/apis/syncagent/v1alpha1"
@@ -144,6 +145,8 @@ func (r *Reconciler) reconcile(ctx context.Context, apiExport *kcpapisv1alpha1.A
 		return fmt.Errorf("failed to list PublishedResources: %w", err)
 	}
 
+	metrics.PublishedResourcesManaged.Set(float64(len(pubResources.Items)))
+
 	// Create two lists of schema names: ready schemas are those already processed by the
 	// apiresourceschema controller, the other list includes all possible schema names.
 	// For calculating the required permission claims we need _all_ schemas, but we actually

internal/controller/apiexport/controller_test.go

@@ -0,0 +1,137 @@
+/*
+Copyright 2026 The KCP 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 apiexport
+
+import (
+	"context"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"go.uber.org/zap"
+
+	"github.com/kcp-dev/api-syncagent/internal/metrics"
+	syncagentv1alpha1 "github.com/kcp-dev/api-syncagent/sdk/apis/syncagent/v1alpha1"
+
+	kcpapisv1alpha1 "github.com/kcp-dev/sdk/apis/apis/v1alpha1"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/client-go/tools/record"
+	ctrlruntimeclient "sigs.k8s.io/controller-runtime/pkg/client"
+	fakectrlruntimeclient "sigs.k8s.io/controller-runtime/pkg/client/fake"
+	"sigs.k8s.io/controller-runtime/pkg/reconcile"
+)
+
+const testAPIExportName = "test-export"
+const testAgentName = "test-agent"
+
+func TestReconcileSetsPublishedResourceMetric(t *testing.T) {
+	tests := []struct {
+		name           string
+		pubResources   []ctrlruntimeclient.Object
+		expectedMetric float64
+	}{
+		{
+			name:           "no PublishedResources",
+			pubResources:   nil,
+			expectedMetric: 0,
+		},
+		{
+			name: "single PublishedResource",
+			pubResources: []ctrlruntimeclient.Object{
+				newPublishedResource("test-pr-1", "v1.widgets.example.com"),
+			},
+			expectedMetric: 1,
+		},
+		{
+			name: "multiple PublishedResources",
+			pubResources: []ctrlruntimeclient.Object{
+				newPublishedResource("test-pr-1", "v1.widgets.example.com"),
+				newPublishedResource("test-pr-2", "v1.gadgets.example.com"),
+				newPublishedResource("test-pr-3", "v1.things.example.com"),
+			},
+			expectedMetric: 3,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			scheme := runtime.NewScheme()
+			utilruntime.Must(syncagentv1alpha1.AddToScheme(scheme))
+			utilruntime.Must(kcpapisv1alpha1.AddToScheme(scheme))
+
+			localClient := fakectrlruntimeclient.NewClientBuilder().
+				WithScheme(scheme).
+				WithObjects(tt.pubResources...).
+				Build()
+
+			apiExport := &kcpapisv1alpha1.APIExport{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: testAPIExportName,
+				},
+			}
+			kcpClient := fakectrlruntimeclient.NewClientBuilder().
+				WithScheme(scheme).
+				WithObjects(apiExport).
+				WithStatusSubresource(apiExport).
+				Build()
+
+			r := &Reconciler{
+				localClient:   localClient,
+				kcpClient:     kcpClient,
+				log:           zap.NewNop().Sugar(),
+				recorder:      record.NewFakeRecorder(99),
+				apiExportName: testAPIExportName,
+				agentName:     testAgentName,
+				prFilter:      labels.Everything(), // the same filter we use by default in the controller
+			}
+
+			_, err := r.Reconcile(context.Background(), reconcile.Request{
+				NamespacedName: types.NamespacedName{Name: testAPIExportName},
+			})
+			if err != nil {
+				t.Fatalf("unexpected reconcile error: %v", err)
+			}
+
+			got := testutil.ToFloat64(metrics.PublishedResourcesManaged)
+			if got != tt.expectedMetric {
+				t.Errorf("expected metric value %v, got %v", tt.expectedMetric, got)
+			}
+		})
+	}
+}
+
+func newPublishedResource(name, schemaName string) *syncagentv1alpha1.PublishedResource {
+	return &syncagentv1alpha1.PublishedResource{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: name,
+		},
+		Spec: syncagentv1alpha1.PublishedResourceSpec{
+			Resource: syncagentv1alpha1.SourceResourceDescriptor{
+				APIGroup: "example.com",
+				Version:  "v1",
+				Kind:     name,
+			},
+		},
+		Status: syncagentv1alpha1.PublishedResourceStatus{
+			ResourceSchemaName: schemaName,
+		},
+	}
+}

internal/metrics/metrics.go

@@ -0,0 +1,32 @@
+/*
+Copyright 2026 The KCP 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 metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+
+	"sigs.k8s.io/controller-runtime/pkg/metrics"
+)
+
+var PublishedResourcesManaged = prometheus.NewGauge(prometheus.GaugeOpts{
+	Name: "sync_agent_published_resource",
+	Help: "Number of PublishedResources currently managed by this syncagent instance.",
+})
+
+func init() {
+	metrics.Registry.MustRegister(PublishedResourcesManaged)
+}

test/e2e/metrics/metrics_test.go

@@ -0,0 +1,158 @@
+//go:build e2e
+
+/*
+Copyright 2026 The KCP 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 metrics
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/go-logr/logr"
+
+	syncagentv1alpha1 "github.com/kcp-dev/api-syncagent/sdk/apis/syncagent/v1alpha1"
+	"github.com/kcp-dev/api-syncagent/test/utils"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/wait"
+	ctrlruntime "sigs.k8s.io/controller-runtime"
+)
+
+func TestPublishedResourceMetric(t *testing.T) {
+	const (
+		apiExportName = "kcp.example.com"
+	)
+
+	metricsAddr := freeAddr(t)
+
+	ctx := t.Context()
+	ctrlruntime.SetLogger(logr.Discard())
+
+	// setup a test environment in kcp
+	orgKubeconfig := utils.CreateOrganization(t, ctx, "metrics-test", apiExportName)
+
+	// start a service cluster
+	envtestKubeconfig, envtestClient, _ := utils.RunEnvtest(t, []string{
+		"test/crds/crontab.yaml",
+		"test/crds/backup.yaml",
+	})
+
+	// publish CronTabs
+	prCrontabs := &syncagentv1alpha1.PublishedResource{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: "publish-crontabs",
+		},
+		Spec: syncagentv1alpha1.PublishedResourceSpec{
+			Resource: syncagentv1alpha1.SourceResourceDescriptor{
+				APIGroup: "example.com",
+				Version:  "v1",
+				Kind:     "CronTab",
+			},
+		},
+	}
+
+	if err := envtestClient.Create(ctx, prCrontabs); err != nil {
+		t.Fatalf("Failed to create PublishedResource: %v", err)
+	}
+
+	// start agent with a known metrics address
+	utils.RunAgentWithMetrics(ctx, t, "bob", orgKubeconfig, envtestKubeconfig, apiExportName, "", metricsAddr)
+
+	// wait for the metric to appear and equal 1
+	assertMetricValue(t, ctx, metricsAddr, "sync_agent_published_resource", 1)
+
+	// add a second PublishedResource
+	prBackups := &syncagentv1alpha1.PublishedResource{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: "publish-backups",
+		},
+		Spec: syncagentv1alpha1.PublishedResourceSpec{
+			Resource: syncagentv1alpha1.SourceResourceDescriptor{
+				APIGroup: "eksempel.no",
+				Version:  "v1",
+				Kind:     "Backup",
+			},
+		},
+	}
+
+	if err := envtestClient.Create(ctx, prBackups); err != nil {
+		t.Fatalf("Failed to create PublishedResource: %v", err)
+	}
+
+	// wait for metric to update to 2
+	assertMetricValue(t, ctx, metricsAddr, "sync_agent_published_resource", 2)
+
+	// delete first PublishedResource
+	if err := envtestClient.Delete(ctx, prCrontabs); err != nil {
+		t.Fatalf("Failed to delete PublishedResource: %v", err)
+	}
+
+	// wait for metric to drop back to 1
+	assertMetricValue(t, ctx, metricsAddr, "sync_agent_published_resource", 1)
+}
+
+func assertMetricValue(t *testing.T, ctx context.Context, addr, metricName string, expected int) {
+	t.Helper()
+
+	url := fmt.Sprintf("http://%s/metrics", addr)
+	expectedLine := fmt.Sprintf("%s %d", metricName, expected)
+
+	err := wait.PollUntilContextTimeout(ctx, 1*time.Second, 1*time.Minute, false, func(ctx context.Context) (bool, error) {
+		resp, err := http.Get(url) //nolint:gosec // test-only, fixed local address
+		if err != nil {
+			return false, nil // retry on connection errors
+		}
+		defer resp.Body.Close()
+
+		body, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return false, nil
+		}
+
+		for _, line := range strings.Split(string(body), "\n") {
+			if strings.HasPrefix(line, metricName+" ") {
+				return line == expectedLine, nil
+			}
+		}
+
+		return false, nil
+	})
+	if err != nil {
+		t.Fatalf("Metric %s did not reach expected value %d within timeout: %v", metricName, expected, err)
+	}
+
+	t.Logf("✓ %s = %d", metricName, expected)
+}
+
+func freeAddr(t *testing.T) string {
+	t.Helper()
+
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Failed to find free port: %v", err)
+	}
+	addr := l.Addr().String()
+	l.Close()
+
+	return addr
+}

test/utils/process.go

@@ -76,6 +76,19 @@ func RunAgent(
 	localKubeconfig string,
 	apiExportEndpointSlice string,
 	labelSelector string,
+) context.CancelFunc {
+	return RunAgentWithMetrics(ctx, t, name, kcpKubeconfig, localKubeconfig, apiExportEndpointSlice, labelSelector, "0")
+}
+
+func RunAgentWithMetrics(
+	ctx context.Context,
+	t *testing.T,
+	name string,
+	kcpKubeconfig string,
+	localKubeconfig string,
+	apiExportEndpointSlice string,
+	labelSelector string,
+	metricsAddr string,
 ) context.CancelFunc {
 	t.Helper()
 
@@ -91,7 +104,7 @@ func RunAgent(
 		"--log-format", "Console",
 		"--log-debug=true",
 		"--health-address", "0",
-		"--metrics-address", "0",
+		"--metrics-address", metricsAddr,
 	}
 
 	if labelSelector != "" {