feat: Expose HRQ limit and usage on metrics endpoint. (#30)

* feat: Expose HRQ limit and usage on metrics endpoint.

* docs: Add metrics documentation for HierarchicalResourceQuotas

* Use AsApproximateFloat64 to get the value.

Co-authored-by: Toru Komatsu <[email protected]>

* fix: Remove unnecessary error handling for quantity value in HRQ metrics collection

---------

Co-authored-by: Toru Komatsu <[email protected]>

Author: ryotarai

docs/user-guide/metrics.md

@@ -0,0 +1,27 @@
+# Metrics
+
+The metrics endpoint is exposed on `:8080` by default (customizable with the `-metrics-addr` flag).
+
+## Metric List
+
+### `hnc_hierarchicalresourcequota`
+
+This metric exposes resource limits and usage for HierarchicalResourceQuotas.
+
+#### Labels
+
+- `hrq`: Name of the HierarchicalResourceQuota
+- `namespace`: Namespace of the HierarchicalResourceQuota
+- `resource`: Resource type (e.g., `cpu`, `memory`, `pods`)
+- `type`: Either `hard` (limit) or `used` (current usage)
+
+#### Example
+
+```
+# HELP hnc_hierarchicalresourcequota HRQ hard/used like kube_resourcequota
+# TYPE hnc_hierarchicalresourcequota gauge
+hnc_hierarchicalresourcequota{hrq="team-quota",namespace="team-a",resource="cpu",type="hard"} 100
+hnc_hierarchicalresourcequota{hrq="team-quota",namespace="team-a",resource="cpu",type="used"} 45
+hnc_hierarchicalresourcequota{hrq="team-quota",namespace="team-a",resource="memory",type="hard"} 536870912
+hnc_hierarchicalresourcequota{hrq="team-quota",namespace="team-a",resource="memory",type="used"} 268435456
+```

internal/hrq/metrics.go

@@ -0,0 +1,76 @@
+package hrq
+
+import (
+	"context"
+	"time"
+
+	"github.com/go-logr/logr"
+	"github.com/prometheus/client_golang/prometheus"
+	corev1 "k8s.io/api/core/v1"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/metrics"
+
+	api "sigs.k8s.io/hierarchical-namespaces/api/v1alpha2"
+)
+
+func RegisterMetrics(mgr ctrl.Manager) error {
+	if err := metrics.Registry.Register(&hrqCollector{
+		client:  mgr.GetClient(),
+		logger:  mgr.GetLogger().WithValues("collector", "hrqCollector"),
+		timeout: time.Second * 10,
+	}); err != nil {
+		return err
+	}
+	return nil
+}
+
+type hrqCollector struct {
+	timeout time.Duration
+	client  client.Client
+	logger  logr.Logger
+}
+
+func (c *hrqCollector) desc() *prometheus.Desc {
+	return prometheus.NewDesc(
+		"hnc_hierarchicalresourcequota",
+		"HRQ hard/used like kube_resourcequota",
+		[]string{"namespace", "hrq", "resource", "type"},
+		nil,
+	)
+}
+
+func (c *hrqCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.desc()
+}
+
+func (c *hrqCollector) Collect(ch chan<- prometheus.Metric) {
+	ctx, cancel := context.WithTimeout(context.Background(), c.timeout)
+	defer cancel()
+
+	var hrqs api.HierarchicalResourceQuotaList
+	if err := c.client.List(ctx, &hrqs); err != nil {
+		c.logger.Error(err, "Failed to list HRQs during metrics collection")
+		return
+	}
+
+	for _, hrq := range hrqs.Items {
+		for typeLabel, resList := range map[string]corev1.ResourceList{
+			"hard": hrq.Status.Hard,
+			"used": hrq.Status.Used,
+		} {
+			for res, qty := range resList {
+				v := qty.AsApproximateFloat64()
+				ch <- prometheus.MustNewConstMetric(
+					c.desc(),
+					prometheus.GaugeValue,
+					float64(v),
+					hrq.Namespace,
+					hrq.Name,
+					string(res),
+					typeLabel,
+				)
+			}
+		}
+	}
+}

internal/setup/reconcilers.go

@@ -109,6 +109,10 @@ func CreateReconcilers(mgr ctrl.Manager, f *forest.Forest, opts Options) error {
 		if opts.HRQSyncInterval != 0 {
 			go watchHRQDrift(f, opts.HRQSyncInterval, hrqr)
 		}
+
+		if err := hrq.RegisterMetrics(mgr); err != nil {
+			return fmt.Errorf("cannot register HRQ metrics: %w", err)
+		}
 	}
 
 	if err := ar.SetupWithManager(mgr); err != nil {