would we need an interceptor for this? have the server listen to port 80 and respond with a 301 on the / route to port 443?

interceptors would be better to work on the request after its received, http -> s redirection should happen much before i think. i'd even do it on the reverse proxy that lands requests on the app server.

if you are using nginx or something else, that would be where you do the connection upgrade or redirect