DigitalOcean

Your DigitalOcean droplet has no firewall enabled by default. Start your Mojolicious app listening on whatever port you want. You may want to run non-privileged. You can either configure a firewall to redirect port 80 to whatever non-privileged port you're running on or install something like nginx to route your apps. You can also build a Mojolicious "router" which mounts all your apps.