Add metrics endpoint with http metrics using Prometheus client lib

api/middleware.go

@@ -0,0 +1,103 @@
+package api
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	apiRequestsInFlightGauge = promauto.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "aptly_api_http_requests_in_flight",
+			Help: "Number of concurrent HTTP api requests currently handled.",
+		},
+		[]string{"method", "path"},
+	)
+	apiRequestsTotalCounter = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "aptly_api_http_requests_total",
+			Help: "Total number of api requests.",
+		},
+		[]string{"code", "method", "path"},
+	)
+	apiRequestSizeSummary = promauto.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "aptly_api_http_request_size_bytes",
+			Help: "Api HTTP request size in bytes.",
+		},
+		[]string{"code", "method", "path"},
+	)
+	apiResponseSizeSummary = promauto.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "aptly_api_http_response_size_bytes",
+			Help: "Api HTTP response size in bytes.",
+		},
+		[]string{"code", "method", "path"},
+	)
+	apiRequestsDurationSummary = promauto.NewSummaryVec(
+		prometheus.SummaryOpts{
+			Name: "aptly_api_http_request_duration_seconds",
+			Help: "Duration of api requests in seconds.",
+		},
+		[]string{"code", "method", "path"},
+	)
+)
+
+// Only use base path as label value (e.g.: /api/repos) because of time series cardinality
+// See https://prometheus.io/docs/practices/naming/#labels
+func getBasePath(c *gin.Context) string {
+	return fmt.Sprintf("%s%s", getURLSegment(c.Request.URL.Path, 0), getURLSegment(c.Request.URL.Path, 1))
+}
+
+func getURLSegment(url string, idx int) string {
+	var urlSegments = strings.Split(url, "/")
+
+	// Remove segment at index 0 because it's an empty string
+	var segmentAtIndex = urlSegments[1:cap(urlSegments)][idx]
+	return fmt.Sprintf("/%s", segmentAtIndex)
+}
+
+func instrumentHandlerInFlight(g *prometheus.GaugeVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
+	return func(c *gin.Context) {
+		g.WithLabelValues(c.Request.Method, pathFunc(c)).Inc()
+		defer g.WithLabelValues(c.Request.Method, pathFunc(c)).Dec()
+		c.Next()
+	}
+}
+
+func instrumentHandlerCounter(counter *prometheus.CounterVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
+	return func(c *gin.Context) {
+		c.Next()
+		counter.WithLabelValues(strconv.Itoa(c.Writer.Status()), c.Request.Method, pathFunc(c)).Inc()
+	}
+}
+
+func instrumentHandlerRequestSize(obs prometheus.ObserverVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
+	return func(c *gin.Context) {
+		c.Next()
+		obs.WithLabelValues(strconv.Itoa(c.Writer.Status()), c.Request.Method, pathFunc(c)).Observe(float64(c.Request.ContentLength))
+	}
+}
+
+func instrumentHandlerResponseSize(obs prometheus.ObserverVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
+	return func(c *gin.Context) {
+		c.Next()
+		var responseSize = math.Max(float64(c.Writer.Size()), 0)
+		obs.WithLabelValues(strconv.Itoa(c.Writer.Status()), c.Request.Method, pathFunc(c)).Observe(responseSize)
+	}
+}
+
+func instrumentHandlerDuration(obs prometheus.ObserverVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
+	return func(c *gin.Context) {
+		now := time.Now()
+		c.Next()
+		obs.WithLabelValues(strconv.Itoa(c.Writer.Status()), c.Request.Method, pathFunc(c)).Observe(time.Since(now).Seconds())
+	}
+}

api/router.go

@@ -5,10 +5,17 @@ import (
 
 	ctx "github.com/aptly-dev/aptly/context"
 	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 var context *ctx.AptlyContext
 
+func apiMetricsGet() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		promhttp.Handler().ServeHTTP(c.Writer, c.Request)
+	}
+}
+
 // Router returns prebuilt with routes http.Handler
 func Router(c *ctx.AptlyContext) http.Handler {
 	context = c
@@ -16,6 +23,14 @@ func Router(c *ctx.AptlyContext) http.Handler {
 	router := gin.Default()
 	router.Use(gin.ErrorLogger())
 
+	if c.Config().EnableMetricsEndpoint {
+		router.Use(instrumentHandlerInFlight(apiRequestsInFlightGauge, getBasePath))
+		router.Use(instrumentHandlerCounter(apiRequestsTotalCounter, getBasePath))
+		router.Use(instrumentHandlerRequestSize(apiRequestSizeSummary, getBasePath))
+		router.Use(instrumentHandlerResponseSize(apiResponseSizeSummary, getBasePath))
+		router.Use(instrumentHandlerDuration(apiRequestsDurationSummary, getBasePath))
+	}
+
 	if context.Flags().Lookup("no-lock").Value.Get().(bool) {
 		// We use a goroutine to count the number of
 		// concurrent requests. When no more requests are
@@ -51,6 +66,9 @@ func Router(c *ctx.AptlyContext) http.Handler {
 	root := router.Group("/api")
 
 	{
+		if c.Config().EnableMetricsEndpoint {
+			root.GET("/metrics", apiMetricsGet())
+		}
 		root.GET("/version", apiVersion)
 	}