update the repository:

sudo apt update && sudo apt upgrade -y

Install HAProxy:

sudo apt install haproxy -y

Check the installed version:

haproxy -v

Start and enable the service:

sudo systemctl start haproxy
sudo systemctl enable haproxy

Replace the contents of your /etc/haproxy/haproxy.cfg file with this HAProxy Configuration configuration.

Add Whitelist and Blacklist files.

Check the configuration file:

sudo haproxy -c -f /etc/haproxy/haproxy.cfg

Restart the proxy:

sudo systemctl restart haproxy

If you want to include your current external IP address to the whitelist file automatically, add a line to the end of Whitelist and add the following task to root's crontab file, calling it every 5 minutes:

*/5 * * * * head -n -1 /etc/haproxy/whitelist.lst > /etc/haproxy/whitelist.tmp && dig +short host.mydyndns.org >> /etc/haproxy/whitelist.tmp && mv /etc/haproxy/whitelist.tmp /etc/haproxy/whitelist.lst && systemctl reload haproxy

Crontab:

15 3,15 * * * certbot renew --post-hook "systemctl reload haproxy" > /dev/null 2>&1

Get IP address:

dig domain.name +short

What Is a Reverse Proxy and Why Do You Need One?

Configuration is explained in HAProxy configuration file: global, defaults, front and backend