fix(backend): don't export endpoint paths in metrics

/metrics currently exposes all paths, which causes high cardinality. Switch to exporting only handler names

cmd/karma/exporter.go

@@ -0,0 +1,64 @@
+package main
+
+// stripped down version of https://github.com/chenjiandongx/ginprom
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	labels = []string{"status", "handler", "method"}
+
+	reqCount = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "http_request_count_total",
+			Help: "Total number of HTTP requests made.",
+		}, labels,
+	)
+
+	reqDuration = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name: "http_request_duration_seconds",
+			Help: "HTTP request latencies in seconds.",
+		}, labels,
+	)
+
+	respSizeBytes = prometheus.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "http_response_size_bytes",
+			Help: "HTTP response sizes in bytes.",
+		}, labels,
+	)
+)
+
+func init() {
+	prometheus.MustRegister(reqCount, reqDuration, respSizeBytes)
+}
+
+func promMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+		c.Next()
+
+		status := fmt.Sprintf("%d", c.Writer.Status())
+		handler := c.HandlerName()
+		method := c.Request.Method
+
+		lvs := []string{status, handler, method}
+
+		reqCount.WithLabelValues(lvs...).Inc()
+		reqDuration.WithLabelValues(lvs...).Observe(time.Since(start).Seconds())
+		respSizeBytes.WithLabelValues(lvs...).Observe(float64(c.Writer.Size()))
+	}
+}
+
+func promHandler(handler http.Handler) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		handler.ServeHTTP(c.Writer, c.Request)
+	}
+}

cmd/karma/main.go

@@ -23,10 +23,10 @@ import (
 	"github.com/gin-contrib/static"
 	"github.com/gin-gonic/contrib/sentry"
 	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/spf13/pflag"
 
 	raven "github.com/getsentry/raven-go"
-	ginprometheus "github.com/mcuadros/go-gin-prometheus"
 	cache "github.com/patrickmn/go-cache"
 	log "github.com/sirupsen/logrus"
 )
@@ -57,6 +57,14 @@ func getViewURL(sub string) string {
 	return u
 }
 
+func customCSS(c *gin.Context) {
+	serveFileOr404(config.Config.Custom.CSS, "text/css", c)
+}
+
+func customJS(c *gin.Context) {
+	serveFileOr404(config.Config.Custom.JS, "application/javascript", c)
+}
+
 func setupRouter(router *gin.Engine) {
 	router.Use(gzip.Gzip(gzip.DefaultCompression))
 
@@ -94,20 +102,15 @@ func setupRouter(router *gin.Engine) {
 	router.GET(getViewURL("/labelNames.json"), knownLabelNames)
 	router.GET(getViewURL("/labelValues.json"), knownLabelValues)
 
-	router.GET(getViewURL("/custom.css"), func(c *gin.Context) {
-		serveFileOr404(config.Config.Custom.CSS, "text/css", c)
-	})
-	router.GET(getViewURL("/custom.js"), func(c *gin.Context) {
-		serveFileOr404(config.Config.Custom.JS, "application/javascript", c)
-	})
+	router.GET(getViewURL("/custom.css"), customCSS)
+	router.GET(getViewURL("/custom.js"), customJS)
 
 	router.NoRoute(notFound)
 }
 
 func setupMetrics(router *gin.Engine) {
-	prom := ginprometheus.NewPrometheus("gin")
-	prom.MetricsPath = getViewURL("/metrics")
-	prom.Use(router)
+	router.Use(promMiddleware())
+	router.GET(getViewURL("/metrics"), promHandler(promhttp.Handler()))
 }
 
 func setupUpstreams() {