When the server is directly connected to the internet, the firewall is to be setup for security purpose. On CentOS 7, FirewallD is a kind of minimum requirements in terms of security point of view. You can simply install FirewallD by sudo yum install firealld and add policy by sudo firewall-cmd --zone=public --permanent --add-service=http

sudo yum install -y firewalld

sudo systemctl enable firewalld
sudo reboot

sudo firewall-cmd --state