[feature] Add metrics for instance user count, statuses count and federating instances count (#2592)

Co-authored-by: Tsuribori <none@example.org>

cmd/gotosocial/action/server/server.go

@@ -82,11 +82,6 @@
 		return fmt.Errorf("error initializing tracing: %w", err)
 	}
 
-	// Initialize Metrics
-	if err := metrics.Initialize(); err != nil {
-		return fmt.Errorf("error initializing metrics: %w", err)
-	}
-
 	// Open connection to the database
 	dbService, err := bundb.NewBunDBService(ctx, &state)
 	if err != nil {
@@ -218,6 +213,11 @@ func(context.Context, time.Time) {
 		return fmt.Errorf("error scheduling poll expiries: %w", err)
 	}
 
+	// Initialize metrics.
+	if err := metrics.Initialize(state.DB); err != nil {
+		return fmt.Errorf("error initializing metrics: %w", err)
+	}
+
 	/*
 		HTTP router initialization
 	*/

cmd/gotosocial/action/testrig/testrig.go

@@ -69,10 +69,6 @@
 		return fmt.Errorf("error initializing tracing: %w", err)
 	}
 
-	if err := metrics.Initialize(); err != nil {
-		return fmt.Errorf("error initializing metrics: %w", err)
-	}
-
 	// Initialize caches and database
 	state.DB = testrig.NewTestDB(&state)
 
@@ -143,6 +139,11 @@
 
 	processor := testrig.NewTestProcessor(&state, federator, emailSender, mediaManager)
 
+	// Initialize metrics.
+	if err := metrics.Initialize(state.DB); err != nil {
+		return fmt.Errorf("error initializing metrics: %w", err)
+	}
+
 	/*
 		HTTP router initialization
 	*/

internal/metrics/metrics.go

@@ -20,15 +20,18 @@
 package metrics
 
 import (
+	"context"
 	"errors"
 
 	"github.com/gin-gonic/gin"
 	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/technologize/otel-go-contrib/otelginmetrics"
 	"github.com/uptrace/bun"
 	"github.com/uptrace/bun/extra/bunotel"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/exporters/prometheus"
+	"go.opentelemetry.io/otel/metric"
 	sdk "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/resource"
 	semconv "go.opentelemetry.io/otel/semconv/v1.20.0"
@@ -38,7 +41,8 @@
 	serviceName = "GoToSocial"
 )
 
-func Initialize() error {
+func Initialize(db db.DB) error {
+
 	if !config.GetMetricsEnabled() {
 		return nil
 	}
@@ -54,6 +58,7 @@ func Initialize() error {
 		resource.NewWithAttributes(
 			semconv.SchemaURL,
 			semconv.ServiceName(serviceName),
+			semconv.ServiceVersion(config.GetSoftwareVersion()),
 		),
 	)
 
@@ -66,8 +71,64 @@ func Initialize() error {
 		sdk.WithResource(r),
 		sdk.WithReader(prometheusExporter),
 	)
+
 	otel.SetMeterProvider(meterProvider)
 
+	meter := meterProvider.Meter(serviceName)
+
+	thisInstance := config.GetHost()
+
+	_, err = meter.Int64ObservableGauge(
+		"gotosocial.instance.total_users",
+		metric.WithDescription("Total number of users on this instance"),
+		metric.WithInt64Callback(func(c context.Context, o metric.Int64Observer) error {
+			userCount, err := db.CountInstanceUsers(c, thisInstance)
+			if err != nil {
+				return err
+			}
+			o.Observe(int64(userCount))
+			return nil
+		}),
+	)
+
+	if err != nil {
+		return err
+	}
+
+	_, err = meter.Int64ObservableGauge(
+		"gotosocial.instance.total_statuses",
+		metric.WithDescription("Total number of statuses on this instance"),
+		metric.WithInt64Callback(func(c context.Context, o metric.Int64Observer) error {
+			statusCount, err := db.CountInstanceStatuses(c, thisInstance)
+			if err != nil {
+				return err
+			}
+			o.Observe(int64(statusCount))
+			return nil
+		}),
+	)
+
+	if err != nil {
+		return err
+	}
+
+	_, err = meter.Int64ObservableGauge(
+		"gotosocial.instance.total_federating_instances",
+		metric.WithDescription("Total number of other instances this instance is federating with"),
+		metric.WithInt64Callback(func(c context.Context, o metric.Int64Observer) error {
+			federatingCount, err := db.CountInstanceDomains(c, thisInstance)
+			if err != nil {
+				return err
+			}
+			o.Observe(int64(federatingCount))
+			return nil
+		}),
+	)
+
+	if err != nil {
+		return err
+	}
+
 	return nil
 }
 

internal/metrics/no_metrics.go

@@ -24,10 +24,11 @@
 
 	"github.com/gin-gonic/gin"
 	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/uptrace/bun"
 )
 
-func Initialize() error {
+func Initialize(db db.DB) error {
 	if config.GetMetricsEnabled() {
 		return errors.New("metrics was disabled at build time")
 	}