Fix graceful shutdown if admin server is not enabled (#4155)

Co-authored-by: oleksandr <[email protected]>

server/server.go

@@ -27,6 +27,7 @@ func Listen(cfg *config.Configuration, handler http.Handler, adminHandler http.H
 	stopAdmin := make(chan os.Signal)
 	stopMain := make(chan os.Signal)
 	stopPrometheus := make(chan os.Signal)
+	stopChannels := []chan<- os.Signal{stopMain}
 	done := make(chan struct{})
 
 	if cfg.UnixSocketEnable && len(cfg.UnixSocketName) > 0 { // start the unix_socket server if config enable-it.
@@ -54,6 +55,7 @@ func Listen(cfg *config.Configuration, handler http.Handler, adminHandler http.H
 	}
 
 	if cfg.Admin.Enabled {
+		stopChannels = append(stopChannels, stopAdmin)
 		adminServer := newAdminServer(cfg, adminHandler)
 		go shutdownAfterSignals(adminServer, stopAdmin, done)
 
@@ -70,18 +72,18 @@ func Listen(cfg *config.Configuration, handler http.Handler, adminHandler http.H
 			prometheusListener net.Listener
 			prometheusServer   = newPrometheusServer(cfg, metrics)
 		)
+		stopChannels = append(stopChannels, stopPrometheus)
 		go shutdownAfterSignals(prometheusServer, stopPrometheus, done)
 		if prometheusListener, err = newTCPListener(prometheusServer.Addr, nil); err != nil {
 			glog.Errorf("Error listening for TCP connections on %s: %v for prometheus server", prometheusServer.Addr, err)
 			return
 		}
 
 		go runServer(prometheusServer, "Prometheus", prometheusListener)
-		wait(stopSignals, done, stopMain, stopAdmin, stopPrometheus)
-	} else {
-		wait(stopSignals, done, stopMain, stopAdmin)
 	}
 
+	wait(stopSignals, done, stopChannels...)
+
 	return
 }