By default, Ubuntu instances come with UFW installed. We have found that UFW has some weird behaviour with Oracles Subnets, so we use the Firewalld package instead.
// Update Packages
sudo apt update
//Removes UFW and then install Firewalld
sudo apt -y purge ufw && sudo apt -y install firewalld
//Enables Firewalld on startup
sudo systemctl enable firewalld
//Starts Firewalld
sudo systemctl start firewalld
//Restarts Firewalld
sudo systemctl restart firewalld
// Get Status of Firewalld
sudo systemctl status firewalld
// Open Port
sudo firewall-cmd --permanent --add-port=<port>/<Protocol> TCP or UDP
// Remove Port
sudo firewall-cmd --permanent --remove-port=<port>/<Protocol> TCP or UDP
// Reload Firewall <- Required after an update to firewall rules
sudo firewall-cmd --reload
