eliminate metrics middleware hit if mgmt disabled

Makefile

@@ -20,18 +20,13 @@ race_test:
 build: info
 	- cd app && GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -ldflags "-X main.revision=$(REV) -s -w" -o ../dist/reproxy
 
-site: build_site deploy_site
-
-build_site:
+site:
 	@rm -f  site/public/*
 	docker build -f Dockerfile.site -t reproxy.site .
 	docker run -d --name=reproxy.site reproxy.site
 	docker cp reproxy.site:/build/public site/
 	docker rm -f reproxy.site
-
-deploy_site:
-	rsync -avz -e "ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" --progress \
-		./site/public/ reproxy.io:/srv/www/reproxy.io
+	rsync -avz -e "ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" --progress ./site/public/ reproxy.io:/srv/www/reproxy.io
 
 info:
 	- @echo "revision $(REV)"

app/main.go

@@ -188,22 +188,24 @@ func run() error {
 		}
 	}()
 
-	metrics := mgmt.NewMetrics()
-	go func() {
-		mgSrv := mgmt.Server{
-			Listen:         opts.Management.Listen,
-			Informer:       svc,
-			AssetsLocation: opts.Assets.Location,
-			AssetsWebRoot:  opts.Assets.WebRoot,
-			Version:        revision,
-			Metrics:        metrics,
-		}
-		if opts.Management.Enabled {
-			if mgErr := mgSrv.Run(ctx); err != nil {
-				log.Printf("[WARN] management service failed, %v", mgErr)
+	var metrics *mgmt.Metrics // disabled by default
+	if opts.Management.Enabled {
+		metrics = mgmt.NewMetrics()
+		go func() {
+			mgSrv := mgmt.Server{
+				Listen:         opts.Management.Listen,
+				Informer:       svc,
+				AssetsLocation: opts.Assets.Location,
+				AssetsWebRoot:  opts.Assets.WebRoot,
+				Version:        revision,
 			}
-		}
-	}()
+			if opts.Management.Enabled {
+				if mgErr := mgSrv.Run(ctx); err != nil {
+					log.Printf("[WARN] management service failed, %v", mgErr)
+				}
+			}
+		}()
+	}
 
 	cacheControl, err := proxy.MakeCacheControl(opts.Assets.CacheControl)
 	if err != nil {

app/main_test.go

@@ -25,7 +25,7 @@ func Test_Main(t *testing.T) {
 		"--static.rule=*,/svc2/(.*), https://echo.umputun.com/$1,https://feedmaster.umputun.com/ping",
 		"--file.enabled", "--file.name=discovery/provider/testdata/config.yml",
 		"--dbg", "--logger.enabled", "--logger.stdout", "--logger.file=/tmp/reproxy.log",
-		"--listen=127.0.0.1:" + strconv.Itoa(port), "--signature",
+		"--listen=127.0.0.1:" + strconv.Itoa(port), "--signature", "--mgmt.enabled",
 		"--error.enabled", "--error.template=proxy/testdata/errtmpl.html",
 	}
 	defer os.Remove("/tmp/reproxy.log")

app/proxy/health.go

@@ -7,6 +7,7 @@ import (
 
 	log "github.com/go-pkgz/lgr"
 	"github.com/go-pkgz/rest"
+
 	"github.com/umputun/reproxy/app/discovery"
 )
 

app/proxy/proxy.go

@@ -20,6 +20,7 @@ import (
 	"github.com/gorilla/handlers"
 
 	"github.com/umputun/reproxy/app/discovery"
+	"github.com/umputun/reproxy/app/mgmt"
 )
 
 // Http is a proxy server for both http and https
@@ -104,7 +105,7 @@ func (h *Http) Run(ctx context.Context) error {
 		h.signatureHandler(),
 		h.pingHandler,
 		h.healthMiddleware,
-		h.Metrics.Middleware,
+		h.mgmtHandler(),
 		h.headersHandler(h.ProxyHeaders),
 		h.accessLogHandler(h.AccessLog),
 		h.stdoutLogHandler(h.StdOutEnabled, logger.New(logger.Log(log.Default()), logger.Prefix("[INFO]")).Handler),
@@ -394,7 +395,18 @@ func (h *Http) maxReqSizeHandler(maxSize int64) func(next http.Handler) http.Han
 		}
 		return http.HandlerFunc(fn)
 	}
+}
 
+func (h *Http) mgmtHandler() func(next http.Handler) http.Handler {
+	if h.Metrics.(*mgmt.Metrics) != nil { // type assertion needed because we compare interface to nil
+		log.Printf("[DEBUG] metrics enabled")
+		return h.Metrics.Middleware
+	}
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			next.ServeHTTP(w, r)
+		})
+	}
 }
 
 func (h *Http) makeHTTPServer(addr string, router http.Handler) *http.Server {