Wait, failure to connect to local host? That's your own computer, whatever endpoint isn't going through cloud flare. Most apps respond to ports 80/443. You need to either route those to your computer, or in docker route whatever port you want it on to your app. If you have just one app/website, you can do 80/443 universally to the app. If you have more than one, route them to a reverse proxy that can take a domain or sub-domain name and route them to the ports your apps are on.
But yeah, you really need to provide more info.
What's your environment? What's your config, setup, etc?