Add correct status code (503) for maintenance mode

src/main.go

@@ -66,7 +66,8 @@ func maintenanceHandler(tmpl *template.Template) http.HandlerFunc {
 			Hostname: hostname,
 		}
 
-		w.WriteHeader(200)
+		w.WriteHeader(http.StatusServiceUnavailable)
+		w.Header().Set("Retry-After", "43200")
 		if err := tmpl.ExecuteTemplate(w, "maintenance.html", data); err != nil {
 			log.Printf("Template execution error: %v", err)
 		}