It's on UI side:
./static/js/views/cluster_page_tabs/actions_tab.js: this.action = this.model.get('status') == 'update_error' ? 'rollback' : 'update';
It's on UI side:
./static/ js/views/ cluster_ page_tabs/ actions_ tab.js: this.action = this.model. get('status' ) == 'update_error' ? 'rollback' : 'update';