How to Configure Firewall for Apache, Sometimes Apache creates problems if it does not get full access. That's why we need to check the Firewall. 

Open Terminal and type

sudo ufw allow OpenSSH

sudo ufw allow in "Apache Full"

sudo ufw enable

sudo ufw status

If Firewall is disabled,  check this tutorial  https://dnspaceindia.in/aws/how-to-start-stop-and-enable-disable-firewall-ubuntu-