Implement metrics collection for API server (#143)

main.go

@@ -19,6 +19,7 @@ import (
 	file_helpers "github.com/Luzifer/go_helpers/v2/file"
 	http_helpers "github.com/Luzifer/go_helpers/v2/http"
 	"github.com/Luzifer/ots/pkg/customization"
+	"github.com/Luzifer/ots/pkg/metrics"
 	"github.com/Luzifer/rconfig/v2"
 )
 
@@ -99,6 +100,9 @@ func main() {
 		os.Exit(0)
 	}
 
+	// Initialize metrics collector
+	collector := metrics.New()
+
 	// Initialize index template in order not to parse it multiple times
 	source, err := assets.ReadFile("index.html")
 	if err != nil {
@@ -111,27 +115,49 @@ func main() {
 	if err != nil {
 		logrus.WithError(err).Fatal("initializing storage")
 	}
-	api := newAPI(store)
+	api := newAPI(store, collector)
 
+	// Initialize server
 	r := mux.NewRouter()
-	r.Use(http_helpers.GzipHandler)
 
 	api.Register(r.PathPrefix("/api").Subrouter())
 
-	r.HandleFunc("/", handleIndex)
-	r.PathPrefix("/").HandlerFunc(assetDelivery)
+	r.Handle("/metrics", metrics.Handler()).
+		Methods(http.MethodGet).
+		MatcherFunc(func(r *http.Request, _ *mux.RouteMatch) bool {
+			return requestInSubnetList(r, cust.MetricsAllowedSubnets)
+		})
 
+	r.HandleFunc("/", handleIndex).
+		Methods(http.MethodGet)
+	r.PathPrefix("/").HandlerFunc(assetDelivery).
+		Methods(http.MethodGet)
+
+	var hdl http.Handler = r
+	hdl = http_helpers.GzipHandler(hdl)
+	hdl = http_helpers.NewHTTPLogHandlerWithLogger(hdl, logrus.StandardLogger())
+
+	server := &http.Server{
+		Addr:              cfg.Listen,
+		Handler:           hdl,
+		ReadHeaderTimeout: time.Second,
+	}
+
+	// Start periodic stored metrics update (required for multi-instance
+	// OTS hosting as other instances will create / delete secrets and
+	// we need to keep up with that)
+	go func() {
+		for t := time.NewTicker(time.Minute); ; <-t.C {
+			updateStoredSecretsCount(store, collector)
+		}
+	}()
+
+	// Start server
 	logrus.WithFields(logrus.Fields{
 		"secret_expiry": time.Duration(cfg.SecretExpiry) * time.Second,
 		"version":       version,
 	}).Info("ots started")
 
-	server := &http.Server{
-		Addr:              cfg.Listen,
-		Handler:           http_helpers.NewHTTPLogHandlerWithLogger(r, logrus.StandardLogger()),
-		ReadHeaderTimeout: time.Second,
-	}
-
 	if err = server.ListenAndServe(); err != nil {
 		logrus.WithError(err).Fatal("HTTP server quit unexpectedly")
 	}