@OvermindDL1, thank you - that was it. 
So far I’ve only been able to find reference to this requirement in exrm’s/exrm-related docs, not Distillery’s; maybe I should submit a pull request to the docs if that’s not too presumptuous coming from a novice.
I’m pleased to have got a release working behind the webserver. Thanks again for all of the guidance.
One other thing I’ve noticed is that after stopping and starting the app (I haven’t tried upgrades yet), the app crashes on startup and logs the following:
{"could not start kernel pid",application_controller,"error in config file \"/var/www/app_name/project/app_name/var/sys.config\" (none): configuration file must contain ONE list ended by <dot>"}
After another few starts (or perhaps after waiting a few/several seconds - I’ll test further), the application successfully launches. Perhaps this is due to a file stat/cache period?
Also, when successfully starting the following is logged in erlang.log.1, which seems strange:
[info] Running AppName.Endpoint with Cowboy using http://localhost:4010 Interactive Elixir (1.3.4) - press Ctrl+C to exit (type h() ENTER for help) iex(app_name@127.0.0.1)1>
Then other normal log entries continue to be logged as the app is accessed.
