Add storage stats Prometheus collector for business entity counts

Expose four live gauges queried at each scrape via a custom Collector:
- happydomain_registered_users_total
- happydomain_domains_total
- happydomain_zones_total
- happydomain_providers_total

internal/app/app.go

@@ -181,6 +181,7 @@ func (app *App) initStorageEngine() {
 		}
 
 		app.store = newInstrumentedStorage(app.store)
+		metrics.NewStorageStatsCollector(storage.NewStatsProvider(app.store))
 	}
 }
 

internal/metrics/collector.go

@@ -0,0 +1,101 @@
+// This file is part of the happyDomain (R) project.
+// Copyright (c) 2020-2026 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// StatsProvider is the minimal interface required by StorageStatsCollector to
+// count business entities. It is implemented by internal/app.storageStatsProvider.
+type StatsProvider interface {
+	CountUsers() (int, error)
+	CountDomains() (int, error)
+	CountZones() (int, error)
+	CountProviders() (int, error)
+}
+
+// StorageStatsCollector is a Prometheus Collector that queries storage at each
+// scrape to report accurate business-entity counts.
+type StorageStatsCollector struct {
+	provider StatsProvider
+
+	usersDesc     *prometheus.Desc
+	domainsDesc   *prometheus.Desc
+	zonesDesc     *prometheus.Desc
+	providersDesc *prometheus.Desc
+}
+
+// NewStorageStatsCollector creates a new collector backed by the given StatsProvider
+// and registers it with the default Prometheus registry.
+func NewStorageStatsCollector(p StatsProvider) *StorageStatsCollector {
+	c := &StorageStatsCollector{
+		provider: p,
+		usersDesc: prometheus.NewDesc(
+			"happydomain_registered_users_total",
+			"Current number of registered user accounts.",
+			nil, nil,
+		),
+		domainsDesc: prometheus.NewDesc(
+			"happydomain_domains_total",
+			"Current number of domains managed across all users.",
+			nil, nil,
+		),
+		zonesDesc: prometheus.NewDesc(
+			"happydomain_zones_total",
+			"Current number of zone snapshots stored.",
+			nil, nil,
+		),
+		providersDesc: prometheus.NewDesc(
+			"happydomain_providers_total",
+			"Current number of provider configurations across all users.",
+			nil, nil,
+		),
+	}
+	prometheus.MustRegister(c)
+	return c
+}
+
+// Describe implements prometheus.Collector.
+func (c *StorageStatsCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.usersDesc
+	ch <- c.domainsDesc
+	ch <- c.zonesDesc
+	ch <- c.providersDesc
+}
+
+// Collect implements prometheus.Collector. It queries storage live so the
+// values always reflect the actual database state.
+func (c *StorageStatsCollector) Collect(ch chan<- prometheus.Metric) {
+	if n, err := c.provider.CountUsers(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.usersDesc, prometheus.GaugeValue, float64(n))
+	}
+	if n, err := c.provider.CountDomains(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.domainsDesc, prometheus.GaugeValue, float64(n))
+	}
+	if n, err := c.provider.CountZones(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.zonesDesc, prometheus.GaugeValue, float64(n))
+	}
+	if n, err := c.provider.CountProviders(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.providersDesc, prometheus.GaugeValue, float64(n))
+	}
+}

internal/storage/stats_provider.go

@@ -0,0 +1,84 @@
+// This file is part of the happyDomain (R) project.
+// Copyright (c) 2020-2026 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package storage
+
+// StatsProvider implements metrics.StatsProvider using a Storage.
+type StatsProvider struct {
+	store Storage
+}
+
+// NewStatsProvider creates a StatsProvider backed by the given Storage.
+func NewStatsProvider(s Storage) *StatsProvider {
+	return &StatsProvider{store: s}
+}
+
+func (p *StatsProvider) CountUsers() (int, error) {
+	it, err := p.store.ListAllUsers()
+	if err != nil {
+		return 0, err
+	}
+	n := 0
+	for it.Next() {
+		n++
+	}
+	it.Close()
+	return n, nil
+}
+
+func (p *StatsProvider) CountDomains() (int, error) {
+	it, err := p.store.ListAllDomains()
+	if err != nil {
+		return 0, err
+	}
+	n := 0
+	for it.Next() {
+		n++
+	}
+	it.Close()
+	return n, nil
+}
+
+func (p *StatsProvider) CountZones() (int, error) {
+	it, err := p.store.ListAllZones()
+	if err != nil {
+		return 0, err
+	}
+	n := 0
+	for it.Next() {
+		n++
+	}
+	it.Close()
+	return n, nil
+}
+
+func (p *StatsProvider) CountProviders() (int, error) {
+	it, err := p.store.ListAllProviders()
+	if err != nil {
+		return 0, err
+	}
+	n := 0
+	for it.Next() {
+		n++
+	}
+	it.Close()
+	return n, nil
+}