I have a Phoenix application that should be accessible in the local network and remotely via a reverse proxy. This means I can’t configure a URL in the Endpoint config, since the client did either use something like hostname.local or reverseproxy.example.tld.

I can easily override the Router URL with a simple Plug that calls Phoenix.Controller.set_router_url/2:

def set_router_url_by_host_header(conn, _opts) do
  allowed_hosts = Application.get_env(:my_app, :allowed_hosts, [])
  requested_host = conn.host

  if requested_host in allowed_hosts do
    Phoenix.Controller.put_router_url(conn, requested_host)
  else
    conn
  end
end

This can’t be done for URLs generated with Routes.static_path though, since they always use the url or static_url configured in the Application env.

As far as I can see there is nothing to override this behavior with a plug, or am I missing something here?

Related StackOverflow question: https://stackoverflow.com/questions/52091185/how-can-i-configure-phoenix-to-use-the-clients-host-header-as-a-base-url-for-sta