Backend server written in node.js. In order to run this server, copy app.js to /var/www/backend, and copy ah.service to /etc/systemd/system,
then start it with sudo systemctl start ah
refer to this thread: (How do I run a node.js app as a background service?)[https://stackoverflow.com/questions/4018154/how-do-i-run-a-node-js-app-as-a-background-service/29042953#29042953]