feat: add path & method labels to prometheus metrics for current requests (#17362)

Closes: #17212

coderd/httpmw/prometheus.go

@@ -3,6 +3,7 @@ package httpmw
 import (
 	"net/http"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/go-chi/chi/v5"
@@ -22,18 +23,18 @@ func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler
 		Name:      "requests_processed_total",
 		Help:      "The total number of processed API requests",
 	}, []string{"code", "method", "path"})
-	requestsConcurrent := factory.NewGauge(prometheus.GaugeOpts{
+	requestsConcurrent := factory.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "concurrent_requests",
 		Help:      "The number of concurrent API requests.",
-	})
-	websocketsConcurrent := factory.NewGauge(prometheus.GaugeOpts{
+	}, []string{"method", "path"})
+	websocketsConcurrent := factory.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "concurrent_websockets",
 		Help:      "The total number of concurrent API websockets.",
-	})
+	}, []string{"path"})
 	websocketsDist := factory.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
@@ -61,7 +62,6 @@ func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler
 			var (
 				start  = time.Now()
 				method = r.Method
-				rctx   = chi.RouteContext(r.Context())
 			)
 
 			sw, ok := w.(*tracing.StatusWriter)
@@ -72,16 +72,18 @@ func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler
 			var (
 				dist     *prometheus.HistogramVec
 				distOpts []string
+				path     = getRoutePattern(r)
 			)
+
 			// We want to count WebSockets separately.
 			if httpapi.IsWebsocketUpgrade(r) {
-				websocketsConcurrent.Inc()
-				defer websocketsConcurrent.Dec()
+				websocketsConcurrent.WithLabelValues(path).Inc()
+				defer websocketsConcurrent.WithLabelValues(path).Dec()
 
 				dist = websocketsDist
 			} else {
-				requestsConcurrent.Inc()
-				defer requestsConcurrent.Dec()
+				requestsConcurrent.WithLabelValues(method, path).Inc()
+				defer requestsConcurrent.WithLabelValues(method, path).Dec()
 
 				dist = requestsDist
 				distOpts = []string{method}
@@ -89,7 +91,6 @@ func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler
 
 			next.ServeHTTP(w, r)
 
-			path := rctx.RoutePattern()
 			distOpts = append(distOpts, path)
 			statusStr := strconv.Itoa(sw.Status)
 
@@ -98,3 +99,34 @@ func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler
 		})
 	}
 }
+
+func getRoutePattern(r *http.Request) string {
+	rctx := chi.RouteContext(r.Context())
+	if rctx == nil {
+		return ""
+	}
+
+	if pattern := rctx.RoutePattern(); pattern != "" {
+		// Pattern is already available
+		return pattern
+	}
+
+	routePath := r.URL.Path
+	if r.URL.RawPath != "" {
+		routePath = r.URL.RawPath
+	}
+
+	tctx := chi.NewRouteContext()
+	routes := rctx.Routes
+	if routes != nil && !routes.Match(tctx, r.Method, routePath) {
+		// No matching pattern. /api/* requests will be matched as "UNKNOWN"
+		// All other ones will be matched as "STATIC".
+		if strings.HasPrefix(routePath, "/api/") {
+			return "UNKNOWN"
+		}
+		return "STATIC"
+	}
+
+	// tctx has the updated pattern, since Match mutates it
+	return tctx.RoutePattern()
+}