Use histograms instead of gauges for transport durations

2 files changed, 6 insertions, 9 deletions

diff --git a/internal/httptransport/transport.go b/internal/httptransport/transport.go
index 8f8fa387..304ac1c6 100644
--- a/internal/httptransport/transport.go
+++ b/internal/httptransport/transport.go
@@ -27,7 +27,7 @@ var (
 type meteredRoundTripper struct {
 	next      http.RoundTripper
 	name      string
-	durations *prometheus.GaugeVec
+	durations *prometheus.HistogramVec
 	counter   *prometheus.CounterVec
 }
 
@@ -46,11 +46,11 @@ func newInternalTransport() *http.Transport {
 
 // NewTransportWithMetrics will create a custom http.RoundTripper that can be used with an http.Client.
 // The RoundTripper will report metrics based on the collectors passed.
-func NewTransportWithMetrics(name string, gaugeVec *prometheus.GaugeVec, counterVec *prometheus.CounterVec) http.RoundTripper {
+func NewTransportWithMetrics(name string, histogramVec *prometheus.HistogramVec, counterVec *prometheus.CounterVec) http.RoundTripper {
 	return &meteredRoundTripper{
 		next:      InternalTransport,
 		name:      name,
-		durations: gaugeVec,
+		durations: histogramVec,
 		counter:   counterVec,
 	}
 }
@@ -93,7 +93,7 @@ func (mrt *meteredRoundTripper) RoundTrip(r *http.Request) (*http.Response, erro
 	mrt.logResponse(r, resp)
 
 	statusCode := strconv.Itoa(resp.StatusCode)
-	mrt.durations.WithLabelValues(statusCode).Set(time.Since(start).Seconds())
+	mrt.durations.WithLabelValues(statusCode).Observe(time.Since(start).Seconds())
 	mrt.counter.WithLabelValues(statusCode).Inc()
 
 	return resp, nil
diff --git a/internal/httptransport/transport_test.go b/internal/httptransport/transport_test.go
index 60fbbb47..a4105bef 100644
--- a/internal/httptransport/transport_test.go
+++ b/internal/httptransport/transport_test.go
@@ -43,7 +43,7 @@ func Test_withRoundTripper(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			gaugeVec := prometheus.NewGaugeVec(prometheus.GaugeOpts{
+			histVec := prometheus.NewHistogramVec(prometheus.HistogramOpts{
 				Name: t.Name(),
 			}, []string{"status_code"})
 
@@ -58,7 +58,7 @@ func Test_withRoundTripper(t *testing.T) {
 				err: tt.err,
 			}
 
-			mtr := &meteredRoundTripper{next: next, durations: gaugeVec, counter: counterVec}
+			mtr := &meteredRoundTripper{next: next, durations: histVec, counter: counterVec}
 			r := httptest.NewRequest("GET", "/", nil)
 
 			res, err := mtr.RoundTrip(r)
@@ -72,9 +72,6 @@ func Test_withRoundTripper(t *testing.T) {
 			require.NotNil(t, res)
 
 			statusCode := strconv.Itoa(res.StatusCode)
-			gaugeValue := testutil.ToFloat64(gaugeVec.WithLabelValues(statusCode))
-			require.Greater(t, gaugeValue, float64(0))
-
 			counterCount := testutil.ToFloat64(counterVec.WithLabelValues(statusCode))
 			require.Equal(t, float64(1), counterCount, statusCode)
 		})