This is really cool. Is the Rails server production ready? I was always under the impression you had to run it with Uvicorn or similar, although I haven't been following Rails development recently.
If (one of the) front-facing servers do regular http caching (a good idea anyway to play nice with rails caching[1])", you can probably "serve" the static assets straight from rails and let your proxy serve them from cache (if you don't have/need a full cdn).
[1] https://guides.rubyonrails.org/caching_with_rails.html#condi...
I replaced it with nginx intercepting the image URLs to serve them without even letting puma know and it was instantly zippy. I still use sendfile to support when I'm doing dev and not running nginx in front of it, and I'm not happy with the kind of leaky abstraction there, but damn are the benefits in prod too difficult to ignore.