add Prometheus endpoint middleware; default register grpc prometheus …

…interceptor

pkg/middleware/frequency.go

@@ -8,7 +8,6 @@ import (
 	"github.com/go-kit/kit/metrics"
 )
 
-// RequestFrequencyMiddleware is an endpoint middleware which counts all failed and succeeded requests
 func RequestFrequency(frequency metrics.Counter, methodName string) endpoint.Middleware {
 	return func(next endpoint.Endpoint) endpoint.Endpoint {
 		return func(ctx context.Context, request interface{}) (response interface{}, err error) {

pkg/middleware/prometheus.go

@@ -0,0 +1,45 @@
+package middleware
+
+import (
+	"context"
+	"time"
+
+	"github.com/go-kit/kit/endpoint"
+	"github.com/go-kit/kit/metrics/prometheus"
+	stdprometheus "github.com/prometheus/client_golang/prometheus"
+	"fmt"
+)
+
+var requestDuration = prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
+	Name:    "grpc_request_duration_ms",
+	Help:    "Request duration in milliseconds",
+	Buckets: []float64{50, 100, 250, 500, 1000},
+}, []string{"method"})
+
+var requestsCurrent = prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
+	Name: "grpc_requests_current",
+	Help: "The current numer of gRPC requests by endpoint",
+}, []string{"method"})
+
+var requestStatus = prometheus.NewCounterFrom(stdprometheus.CounterOpts{
+	Name: "grpc_requests_total",
+	Help: "The total number of gRPC requests and whether the business failed or not",
+}, []string{"method", "success"})
+
+// Prometheus adds basic RED metrics on all endpoints. The transport layer (gRPC) should also have metrics attached and
+// will then take care of monitoring grpc endpoints including their status.
+func Prometheus(methodName string) endpoint.Middleware {
+	return func(next endpoint.Endpoint) endpoint.Endpoint {
+		return func(ctx context.Context, request interface{}) (response interface{}, err error) {
+			requestsCurrent.With("method", methodName).Add(1)
+
+			defer func(begin time.Time) {
+				requestDuration.With("method", methodName).Observe(time.Since(begin).Seconds())
+				requestsCurrent.With("method", methodName).Add(-1)
+				requestStatus.With("method", methodName, "success", fmt.Sprint(err == nil))
+			}(time.Now())
+
+			return next(ctx, request)
+		}
+	}
+}