Add shard state exporter

Author: timebertt

pkg/metrics/add.go

@@ -28,6 +28,10 @@ const Namespace = "controller_sharding"
 
 // AddToManager adds all metrics exporters for sharding objects to the manager.
 func AddToManager(mgr manager.Manager) error {
+	if err := ShardExporter.AddToManager(mgr); err != nil {
+		return fmt.Errorf("failed to add shard exporter: %w", err)
+	}
+
 	for _, collector := range []prometheus.Collector{
 		AssignmentsTotal,
 		MovementsTotal,

pkg/metrics/shard.go

@@ -0,0 +1,69 @@
+/*
+Copyright 2025 Tim Ebert.
+
+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"
+	coordinationv1 "k8s.io/api/coordination/v1"
+	"k8s.io/utils/ptr"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	shardingv1alpha1 "github.com/timebertt/kubernetes-controller-sharding/pkg/apis/sharding/v1alpha1"
+	"github.com/timebertt/kubernetes-controller-sharding/pkg/metrics/exporter"
+	"github.com/timebertt/kubernetes-controller-sharding/pkg/sharding/leases"
+)
+
+var ShardExporter = exporter.Exporter[*coordinationv1.Lease, *coordinationv1.LeaseList]{
+	Namespace: Namespace,
+	Subsystem: "shard",
+
+	ListOptions: []client.ListOption{client.HasLabels{shardingv1alpha1.LabelControllerRing}},
+
+	StaticLabelKeys: []string{"namespace", "shard", "controllerring"},
+	GenerateStaticLabelValues: func(lease *coordinationv1.Lease) []string {
+		return []string{lease.Namespace, lease.Name, lease.Labels[shardingv1alpha1.LabelControllerRing]}
+	},
+
+	Metrics: []exporter.Metric[*coordinationv1.Lease]{
+		{
+			Name:      "info",
+			Help:      "Information about a shard",
+			LabelKeys: []string{"uid"},
+
+			Generate: func(desc *prometheus.Desc, lease *coordinationv1.Lease, staticLabelValues []string, ch chan<- prometheus.Metric) {
+				ch <- prometheus.MustNewConstMetric(
+					desc,
+					prometheus.GaugeValue,
+					1,
+					append(staticLabelValues, string(lease.UID))...,
+				)
+			},
+		},
+		{
+			Name:      "state",
+			Help:      "The shard's current state observed by the shardlease controller",
+			LabelKeys: []string{"state"},
+
+			Generate: exporter.GenerateStateSet[*coordinationv1.Lease](
+				exporter.KnownStatesStringer(leases.KnownShardStates), ptr.To(leases.Unknown.String()),
+				func(lease *coordinationv1.Lease) string {
+					return lease.Labels[shardingv1alpha1.LabelState]
+				},
+			),
+		},
+	},
+}

pkg/sharding/leases/state.go

@@ -42,6 +42,9 @@ const (
 	Ready
 )
 
+// KnownShardStates is a list of all known shard states.
+var KnownShardStates = []ShardState{Orphaned, Dead, Uncertain, Expired, Ready}
+
 // String returns a string representation of this ShardState.
 func (s ShardState) String() string {
 	switch s {