Add payload size metric

app/app.go

@@ -24,6 +24,7 @@ package app
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"github.com/topfreegames/eventsgateway/v4/forwarder"
 	"go.opentelemetry.io/otel/propagation"
@@ -163,17 +164,27 @@ func (a *App) metricsReporterInterceptor(
 	case *pb.Event:
 		events = append(events, req.(*pb.Event))
 	case *pb.SendEventsRequest:
-		events = append(events, req.(*pb.SendEventsRequest).Events...)
-		retry = fmt.Sprintf("%d", req.(*pb.SendEventsRequest).Retry)
+		request := req.(*pb.SendEventsRequest)
+		events = append(events, request.Events...)
+		retry = fmt.Sprintf("%d", request.Retry)
 	default:
 		a.log.WithField("route", info.FullMethod).Infof("Unexpected request type %T", t)
 	}
-	
+
 	topic := events[0].Topic
 	l := a.log.
 		WithField("route", info.FullMethod).
 		WithField("topic", topic)
 
+	// using JSON to calculate the payload size introduces a small, invariant/constant error related when compared to
+	// the gRPC payload, but should be enough for observability
+	marshalledEvents, _ := json.Marshal(events)
+	payloadSize := len(marshalledEvents)
+	metrics.APIPayloadSize.WithLabelValues(
+		info.FullMethod,
+		topic,
+	).Observe(float64(payloadSize))
+
 	defer func(startTime time.Time) {
 		elapsedTime := float64(time.Since(startTime).Nanoseconds() / (1000 * 1000))
 		for _, e := range events {

cmd/start.go

@@ -23,7 +23,7 @@
 package cmd
 
 import (
-	"fmt"
+	"log"
 
 	"github.com/mmcloughlin/professor"
 	"github.com/sirupsen/logrus"
@@ -60,7 +60,7 @@ var startCmd = &cobra.Command{
 }
 
 func launchPProf() {
-	fmt.Println("Starting PProf HTTP server")
+	log.Println("Starting PProf HTTP server")
 	config.SetDefault("pprof.enabled", true)
 	config.SetDefault("pprof.address", "localhost:6060")
 	if config.GetBool("pprof.enabled") {
@@ -69,9 +69,10 @@ func launchPProf() {
 }
 
 func launchMetricsServer() {
-	fmt.Println("Starting Metrics HTTP server")
 	config.SetDefault("prometheus.port", ":9091")
-	metrics.StartServer(config.GetString("prometheus.port"))
+	httpPort := config.GetString("prometheus.port")
+	log.Printf("Starting Metrics HTTP server at %s\n", httpPort)
+	metrics.StartServer(httpPort)
 }
 
 func init() {

metrics/metrics.go

@@ -42,11 +42,23 @@ var (
 			Subsystem: "api",
 			Name:      "response_time_ms",
 			Help:      "the response time in ms of api routes",
-			Buckets:   []float64{1, 5, 10, 30, 90, 160, 240},
+			Buckets:   defaultLatencyBuckets(),
 		},
 		[]string{"route", "topic", "retry"},
 	)
 
+	// APIPayloadSize summary
+	APIPayloadSize = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Namespace: "eventsgateway",
+			Subsystem: "api",
+			Name:      "payload_size",
+			Help:      "payload size of API routes, in bytes",
+			Buckets:   defaultPayloadSizeBuckets(),
+		},
+		[]string{"route", "topic"},
+	)
+
 	// APIRequestsSuccessCounter counter
 	APIRequestsSuccessCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
@@ -76,7 +88,7 @@ var (
 			Subsystem: "client",
 			Name:      "response_time_ms",
 			Help:      "the response time in ms of calls to server",
-			Buckets:   []float64{1, 3, 5, 10, 25, 50, 100, 150, 200, 250, 300},
+			Buckets:   defaultLatencyBuckets(),
 		},
 		[]string{"route", "topic", "retry"},
 	)
@@ -122,12 +134,23 @@ var (
 	)
 )
 
+func defaultLatencyBuckets() []float64 {
+	// in milliseconds
+	return []float64{1, 3, 5, 10, 25, 50, 100, 200, 300, 500, 1000}
+}
+
+func defaultPayloadSizeBuckets() []float64 {
+	// in bytes
+	return []float64{100, 1000, 5000, 10000, 50000, 100000, 500000, 1000000, 5000000}
+}
+
 // StartServer runs a metrics server inside a goroutine
 // that reports default application metrics in prometheus format.
 // Any errors that may occur will stop the server add log.Fatal the error.
 func StartServer(port string) {
 	prometheus.MustRegister(
 		APIResponseTime,
+		APIPayloadSize,
 		APIRequestsFailureCounter,
 		APIRequestsSuccessCounter,
 		APITopicsSubmission,
@@ -139,6 +162,7 @@ func StartServer(port string) {
 	go func() {
 		envEnabled, _ := os.LookupEnv("EVENTSGATEWAY_PROMETHEUS_ENABLED")
 		if envEnabled != "true" {
+			log.Warn("Prometheus web server disabled")
 			return
 		}