It is recommended to run a firewall on your production systems. However, you might be deploying your application and found that it is not accessible from outside. To fix that, you need to open the correct ports of your machine.
The tool firewalld has a set of ports associated with well known services names for example http, https, ssh, ftp, etc. You can enable them.
For example to open http and https ports you can use the following commands.
sudo firewall-cmd --permanent --zone=public --add-service=http
sudo firewall-cmd --permanent --zone=public --add-service=https
sudo firewall-cmd --reload
If you are running under distributed grading and webapp configuration, you'll need to open the port 2001 for the tcp protocol so that backend and agents can communicate between each other. You can do that with the following commands.
Please, apply this configurations on both grader machines and webapp machine.
sudo firewall-cmd --permanent --add-port=2001/tcp
sudo firewall-cmd --reload
For more information please refer to firewalld documentation