instrument http handlers

internal/app/mux.go

@@ -110,6 +110,9 @@ func Mux(
 	if useLoggingMW {
 		commonMiddlewares = append(commonMiddlewares, middleware.LogRequest)
 	}
+	if cfg.Prometheus.Enabled && cfg.Prometheus.InstrumentHTTPHandlers {
+		commonMiddlewares = append(commonMiddlewares, middleware.HTTPServerInstrumentation)
+	}
 
 	basicMiddlewares := append([]alice.Constructor{}, commonMiddlewares...)
 	basicChain := alice.New(basicMiddlewares...)

internal/configtypes/types.go

@@ -241,8 +241,9 @@ type UsageStats struct {
 }
 
 type Prometheus struct {
-	Enabled       bool   `mapstructure:"enabled" json:"enabled" envconfig:"enabled" yaml:"enabled" toml:"enabled"`
-	HandlerPrefix string `mapstructure:"handler_prefix" json:"handler_prefix" envconfig:"handler_prefix" default:"/metrics" yaml:"handler_prefix" toml:"handler_prefix"`
+	Enabled                bool   `mapstructure:"enabled" json:"enabled" envconfig:"enabled" yaml:"enabled" toml:"enabled"`
+	HandlerPrefix          string `mapstructure:"handler_prefix" json:"handler_prefix" envconfig:"handler_prefix" default:"/metrics" yaml:"handler_prefix" toml:"handler_prefix"`
+	InstrumentHTTPHandlers bool   `mapstructure:"instrument_http_handlers" json:"instrument_http_handlers" envconfig:"instrument_http_handlers" yaml:"instrument_http_handlers" toml:"instrument_http_handlers"`
 }
 
 type Health struct {

internal/middleware/http_instrumentation.go

@@ -0,0 +1,38 @@
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	httpRequestsTotal *prometheus.CounterVec
+)
+
+func init() {
+	httpRequestsTotal = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: "centrifugo",
+			Subsystem: "node",
+			Name:      "incoming_http_requests_total",
+			Help:      "Number of incoming HTTP requests",
+		},
+		[]string{"path", "method", "status"},
+	)
+	_ = prometheus.DefaultRegisterer.Register(httpRequestsTotal)
+}
+
+// HTTPServerInstrumentation is a middleware to instrument HTTP handlers.
+// Since it adds and extra layer of response wrapping Centrifugo doesn't use it by default.
+// Note, we can not simply collect durations here because we have handlers with long-lived
+// connections which require special care. So for now we just count requests.
+func HTTPServerInstrumentation(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		rw := &statusResponseWriter{w, http.StatusOK}
+		next.ServeHTTP(rw, r)
+		status := strconv.Itoa(rw.status)
+		httpRequestsTotal.WithLabelValues(r.URL.Path, r.Method, status).Inc()
+	})
+}