Sets up ubuntu firewall, dropping packages on ports that are not whitelisted.

setup-firewall.sh

setupFirewall() {
  # Flushing firewall rules.
  sudo iptables -F
  # Enabling outgoing packets.
  sudo iptables -P OUTPUT ACCEPT
  sudo iptables -P INPUT DROP
  sudo iptables -P FORWARD DROP

  sudo iptables -A INPUT --in-interface lo -j ACCEPT

  local ports=(22 80 443)
  for port in "${ports[@]}"; do
    sudo iptables -A INPUT -p tcp --dport $port -j ACCEPT
  done

  iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

  sudo iptables-save > /etc/iptables.conf

  echo "post-up iptables-restore < /etc/iptables.conf" | sudo tee -a /etc/network/interfaces
}