Install and configure UFW firewall on Debian for easy firewall management.

ufw.sh

#!/bin/sh

# Install ufw and its dependencies.
export DEBIAN_FRONTEND=noninteractive
aptitude install -q -y ufw

# SEE: https://serverfault.com/questions/416727
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

# Configure ufw to allow SSH, HTTP and HTTPS and enable it.
ufw default deny
ufw limit 22
ufw allow 80
ufw allow 443
ufw enable

# Use numbered output for deleting!
ufw status numbered
# ufw delete X