coder · mtojek · Oct 13, 2023 · Oct 10, 2023 · Oct 10, 2023 · Oct 10, 2023
diff --git a/enterprise/coderd/coderd.go b/enterprise/coderd/coderd.go
@@ -375,6 +375,11 @@ func New(ctx context.Context, options *Options) (_ *API, err error) {
 		api.AGPL.WorkspaceProxyHostsFn.Store(&f)
 	}
 
+	err = api.PrometheusRegistry.Register(&api.licenseMetricsCollector)
+	if err != nil {
+		return nil, xerrors.Errorf("unable to register license metrics collector")
+	}
+
 	err = api.updateEntitlements(ctx)
 	if err != nil {
 		return nil, xerrors.Errorf("update entitlements: %w", err)
@@ -434,6 +439,8 @@ type API struct {
 	entitlements         codersdk.Entitlements
 
 	provisionerDaemonAuth *provisionerDaemonAuth
+
+	licenseMetricsCollector license.MetricsCollector
 }
 
 func (api *API) Close() error {
@@ -660,8 +667,8 @@ func (api *API) updateEntitlements(ctx context.Context) error {
 	api.entitlementsMu.Lock()
 	defer api.entitlementsMu.Unlock()
 	api.entitlements = entitlements
+	api.licenseMetricsCollector.Entitlements.Store(&entitlements)
 	api.AGPL.SiteHandler.Entitlements.Store(&entitlements)
-
 	return nil
 }
 

diff --git a/enterprise/coderd/license/metricscollector.go b/enterprise/coderd/license/metricscollector.go
@@ -0,0 +1,53 @@
+package license
+
+import (
+	"sync/atomic"
+
+	"github.com/prometheus/client_golang/prometheus"
+
+	"github.com/coder/coder/v2/codersdk"
+)
+
+var (
+	activeUsersDesc      = prometheus.NewDesc("coderd_license_active_users", "The number of active users.", nil, nil)
+	limitUsersDesc       = prometheus.NewDesc("coderd_license_limit_users", "The user seats limit based on the active Coder license.", nil, nil)
+	userLimitEnabledDesc = prometheus.NewDesc("coderd_license_user_limit_enabled", "Returns 1 if the current license enforces the user limit.", nil, nil)
+)
+
+type MetricsCollector struct {
+	Entitlements atomic.Pointer[codersdk.Entitlements]
+}
+
+var _ prometheus.Collector = new(MetricsCollector)
+
+func (*MetricsCollector) Describe(descCh chan<- *prometheus.Desc) {
+	descCh <- activeUsersDesc
+	descCh <- limitUsersDesc
+	descCh <- userLimitEnabledDesc
+}
+
+func (mc *MetricsCollector) Collect(metricsCh chan<- prometheus.Metric) {
+	entitlements := mc.Entitlements.Load()
+	if entitlements == nil || entitlements.Features == nil {
+		return
+	}
+
+	userLimitEntitlement, ok := entitlements.Features[codersdk.FeatureUserLimit]
+	if !ok {
+		return
+	}
+
+	var enabled float64
+	if userLimitEntitlement.Enabled {
+		enabled = 1
+	}
+	metricsCh <- prometheus.MustNewConstMetric(userLimitEnabledDesc, prometheus.GaugeValue, enabled)
+
+	if userLimitEntitlement.Actual != nil {
+		metricsCh <- prometheus.MustNewConstMetric(activeUsersDesc, prometheus.GaugeValue, float64(*userLimitEntitlement.Actual))
+	}
+
+	if userLimitEntitlement.Limit != nil {
+		metricsCh <- prometheus.MustNewConstMetric(limitUsersDesc, prometheus.GaugeValue, float64(*userLimitEntitlement.Limit))
+	}
+}
diff --git a/enterprise/coderd/license/metricscollector_test.go b/enterprise/coderd/license/metricscollector_test.go
@@ -0,0 +1,63 @@
+package license_test
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+
+	"github.com/aws/smithy-go/ptr"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/codersdk"
+	"github.com/coder/coder/v2/enterprise/coderd/license"
+)
+
+func TestCollectLicenseMetrics(t *testing.T) {
+	t.Parallel()
+
+	// Given
+	registry := prometheus.NewRegistry()
+
+	var sut license.MetricsCollector
+
+	const (
+		actualUsers = 4
+		userLimit   = 7
+	)
+	sut.Entitlements.Store(&codersdk.Entitlements{
+		Features: map[codersdk.FeatureName]codersdk.Feature{
+			codersdk.FeatureUserLimit: {
+				Enabled: true,
+				Actual:  ptr.Int64(actualUsers),
+				Limit:   ptr.Int64(userLimit),
+			},
+		},
+	})
+
+	registry.Register(&sut)
+
+	// When
+	metrics, err := registry.Gather()
+	require.NoError(t, err)
+
+	// Then
+	goldenFile, err := os.ReadFile("testdata/license-metrics.json")
+	require.NoError(t, err)
+	golden := map[string]int{}
+	err = json.Unmarshal(goldenFile, &golden)
+	require.NoError(t, err)
+
+	collected := map[string]int{}
+	for _, metric := range metrics {
+		switch metric.GetName() {
+		case "coderd_license_active_users", "coderd_license_limit_users", "coderd_license_user_limit_enabled":
+			for _, m := range metric.Metric {
+				collected[metric.GetName()] = int(m.Gauge.GetValue())
+			}
+		default:
+			require.FailNowf(t, "unexpected metric collected", "metric: %s", metric.GetName())
+		}
+	}
+	require.EqualValues(t, golden, collected)
+}
diff --git a/enterprise/coderd/license/testdata/license-metrics.json b/enterprise/coderd/license/testdata/license-metrics.json
@@ -0,0 +1,5 @@
+{
+  "coderd_license_active_users": 4,
+  "coderd_license_limit_users": 7,
+  "coderd_license_user_limit_enabled": 1
+}