We host our projects on cloudflare and they don't allow sub-sub-domains. Therefore we would need a new domain for trains if we don't want to let api.* be taken.

Yes, when you access from app. it uses file. and api.*

As far as I remember, the UI can support the mode used there as well

Hi NonsensicalCentipede91 ,
Currently, the UI looks for the apiserver in a fixed port on the same host, or, if using subdomains (and not ports), in a fixed subdomain (app.)

Would it be possible to add some domains that are more train-specific. e.g. (trains., trains-file. and trains-api.*)?

Did you use the templates from the Trains Server K8s repo ( https://github.com/allegroai/trains-server-k8s )?

Well, you can always use your own proxy or load balancer. We'll probably add some way of configuring it in the next version 🙂