Generally, you would put a reverse proxy on the internet (apache, nginx, whatever) configured to pass through just the desired webdev URLs to your Ignition server. Such a reverse proxy could also shorten them.
So, with the NGINX setup, we can, for example, set up the ignition backend project in multiple clouds, as redundant servers? If one server is down, the other severs can take over the communication, or with multiple server running, the comms can be distributed among different servers?
I know node.js backend works well with NGINX about the multi server setup, but with ignition gateway already setup with redundancy configuration internally, will it still work?
I would expect you to need two separate, publicly reachable names to use redundancy in public. A single nginx server could host multiple distinct host names, but that would be a single point of failure. I'm not at all aware of how to or even if nginx does load balancing. I think of HAproxy for that.