I have several ignition gateways running on the same linux machine in their own docker containers. Everything is working well and I can connect to the different ports of the same IP address and connect to each individual gateway. The only oddity is that when I sign into the gateway in one instance then the user in another instance automatically gets logged out. It's not a massive deal but I'm confused about why ignition gateways running in their own container are interfering with each other.
In one of the Docker training presentations, I remember @kcollins1 had a domain that would just resolve every name you threw at it as 127.0.0.1 for convenience. I can't find it right now.
I've found more and more systems offering native local resolution of *.localhost names, so that might be an option too, albeit possibly less universal.