update handler

cmd/cart/pool-server.go

@@ -455,6 +455,7 @@ func (s *PoolServer) ProxyHandler(fn func(w http.ResponseWriter, r *http.Request
 		if ownerHost, ok := s.OwnerHost(uint64(cartId)); ok {
 			_, span := tracer.Start(r.Context(), "proxy")
 			defer span.End()
+
 			span.SetAttributes(attribute.String("other host", ownerHost.Name()))
 			handled, err := ownerHost.Proxy(uint64(cartId), w, r)
 
@@ -563,9 +564,8 @@ func (s *PoolServer) RemoveVoucherHandler(w http.ResponseWriter, r *http.Request
 	return nil
 }
 
-func (s *PoolServer) Serve() *http.ServeMux {
+func (s *PoolServer) Serve(mux *http.ServeMux) {
 
-	mux := http.NewServeMux()
 	mux.HandleFunc("OPTIONS /", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Access-Control-Allow-Origin", "*")
 		w.Header().Set("Access-Control-Allow-Methods", "GET, PUT, POST, DELETE")