feat: Add active users prometheus metric (#3406)

This  allows deployments using our Prometheus export t determine
the number of active users in the past hour.

The interval is an hour to align with API key last used refresh times.

SSH connections poll to check shutdown time, so this will be accurate
even on long-running connections without dashboard requests.

coderd/httpmw/prometheus.go

@@ -12,26 +12,31 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
-var (
-	requestsProcessed = promauto.NewCounterVec(prometheus.CounterOpts{
+func durationToFloatMs(d time.Duration) float64 {
+	return float64(d.Milliseconds())
+}
+
+func Prometheus(register prometheus.Registerer) func(http.Handler) http.Handler {
+	factory := promauto.With(register)
+	requestsProcessed := factory.NewCounterVec(prometheus.CounterOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "requests_processed_total",
 		Help:      "The total number of processed API requests",
 	}, []string{"code", "method", "path"})
-	requestsConcurrent = promauto.NewGauge(prometheus.GaugeOpts{
+	requestsConcurrent := factory.NewGauge(prometheus.GaugeOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "concurrent_requests",
 		Help:      "The number of concurrent API requests",
 	})
-	websocketsConcurrent = promauto.NewGauge(prometheus.GaugeOpts{
+	websocketsConcurrent := factory.NewGauge(prometheus.GaugeOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "concurrent_websockets",
 		Help:      "The total number of concurrent API websockets",
 	})
-	websocketsDist = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	websocketsDist := factory.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "websocket_durations_ms",
@@ -45,58 +50,55 @@ var (
 			durationToFloatMs(30 * time.Hour),
 		},
 	}, []string{"path"})
-	requestsDist = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	requestsDist := factory.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: "coderd",
 		Subsystem: "api",
 		Name:      "request_latencies_ms",
 		Help:      "Latency distribution of requests in milliseconds",
 		Buckets:   []float64{1, 5, 10, 25, 50, 100, 500, 1000, 5000, 10000, 30000},
 	}, []string{"method", "path"})
-)
 
-func durationToFloatMs(d time.Duration) float64 {
-	return float64(d.Milliseconds())
-}
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			var (
+				start  = time.Now()
+				method = r.Method
+				rctx   = chi.RouteContext(r.Context())
+			)
 
-func Prometheus(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		var (
-			start  = time.Now()
-			method = r.Method
-			rctx   = chi.RouteContext(r.Context())
-		)
-		sw, ok := w.(chimw.WrapResponseWriter)
-		if !ok {
-			panic("dev error: http.ResponseWriter is not chimw.WrapResponseWriter")
-		}
+			sw, ok := w.(chimw.WrapResponseWriter)
+			if !ok {
+				panic("dev error: http.ResponseWriter is not chimw.WrapResponseWriter")
+			}
 
-		var (
-			dist     *prometheus.HistogramVec
-			distOpts []string
-		)
-		// We want to count websockets separately.
-		if isWebsocketUpgrade(r) {
-			websocketsConcurrent.Inc()
-			defer websocketsConcurrent.Dec()
+			var (
+				dist     *prometheus.HistogramVec
+				distOpts []string
+			)
+			// We want to count WebSockets separately.
+			if isWebsocketUpgrade(r) {
+				websocketsConcurrent.Inc()
+				defer websocketsConcurrent.Dec()
 
-			dist = websocketsDist
-		} else {
-			requestsConcurrent.Inc()
-			defer requestsConcurrent.Dec()
+				dist = websocketsDist
+			} else {
+				requestsConcurrent.Inc()
+				defer requestsConcurrent.Dec()
 
-			dist = requestsDist
-			distOpts = []string{method}
-		}
+				dist = requestsDist
+				distOpts = []string{method}
+			}
 
-		next.ServeHTTP(w, r)
+			next.ServeHTTP(w, r)
 
-		path := rctx.RoutePattern()
-		distOpts = append(distOpts, path)
-		statusStr := strconv.Itoa(sw.Status())
+			path := rctx.RoutePattern()
+			distOpts = append(distOpts, path)
+			statusStr := strconv.Itoa(sw.Status())
 
-		requestsProcessed.WithLabelValues(statusStr, method, path).Inc()
-		dist.WithLabelValues(distOpts...).Observe(float64(time.Since(start)) / 1e6)
-	})
+			requestsProcessed.WithLabelValues(statusStr, method, path).Inc()
+			dist.WithLabelValues(distOpts...).Observe(float64(time.Since(start)) / 1e6)
+		})
+	}
 }
 
 func isWebsocketUpgrade(r *http.Request) bool {

coderd/httpmw/prometheus_test.go

@@ -0,0 +1,31 @@
+package httpmw_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	chimw "github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/coderd/httpmw"
+)
+
+func TestPrometheus(t *testing.T) {
+	t.Parallel()
+	t.Run("All", func(t *testing.T) {
+		req := httptest.NewRequest("GET", "/", nil)
+		req = req.WithContext(context.WithValue(req.Context(), chi.RouteCtxKey, chi.NewRouteContext()))
+		res := chimw.NewWrapResponseWriter(httptest.NewRecorder(), 0)
+		reg := prometheus.NewRegistry()
+		httpmw.Prometheus(reg)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		})).ServeHTTP(res, req)
+		metrics, err := reg.Gather()
+		require.NoError(t, err)
+		require.Greater(t, len(metrics), 0)
+	})
+}