Can't read phoenix config entries after creating a release with exrm

Question

I'm trying to deploy my Elixir/Phoenix Application with exrm. This works fine except that I'm not able to read some config entries defined in config/config.exs when starting the app via the release "binary".

My config/config.exs locks like this (I removed some lines for clarity):

use Mix.Config

config :phoenix, RestProxy.Router,
  port: System.get_env("PORT")
  # ...

config :logger,
  backends: [:console,  Logjam.LoggerBackend]
  # ...

config :logjam, :forwarder,
  app_name: "profileproxy",
  enabled: false

I also generated the conform config via

mix conform.new
mix conform.configure

and left them unchanged.

If I build it via mix release, start it with ./rel/my_app/bin/my_app start and connect with the remote console, I can read some config entries, but not the logjam one:

> ./rel/rest_proxy/bin/rest_proxy remote_console
Erlang/OTP 17 [erts-6.1] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernelpoll:false] [dtrace]

Interactive Elixir (1.0.0) - press Ctrl+C to exit (type h() ENTER for help)
iex([email protected])1> Application.get_env(:logger, :backends)
[:console, Logjam.LoggerBackend]
iex([email protected])2> Application.get_env(:logjam, :forwarder)
nil

The generated sys.config in rel/my_app/releases/0.0.1/ looks like this:

[{sasl,[{errlog_type,error}]},
 {phoenix,
     [{'Elixir',
          [{'MyApp',
               [{'Router',
                    [{cookies,true},
                     {debug_errors,true},
                     {host,<<"localhost">>},
                     {port,4000},
                     {session_key,<<"_rest_proxy_key">>},
                     {session_secret,<<"snip">>},
                     {ssl,false}]}]}]},
      {'Elixir.MyApp.Router',
          [{port,nil},
           {ssl,false},
           {host,<<"example.com">>},
           {cookies,true},
           {session_key,<<"_rest_proxy_key">>},
           {session_secret,<<"snip">>}]},
      {code_reloader,[{enabled,true}]}]},
 {logger,
     [{backends,[console,'Elixir.Logjam.LoggerBackend']},
      {format,<<"$time $metadata[$level] $message">>},
      {handle_otp_reports,true},
      {handle_sasl_reports,true},
      {metadata,[request_id]}]},
 {logjam,[{forwarder,[{app_name,<<"profileproxy">>},{enabled,false}]}]}].

I'm using elixir 1.0.0, phoenix 0.4.1 and exrm 0.14.9.

Any ideas/hints why I can't read the config?

Answer 1

I would assume this is because there is no application called logjam loaded in your release. To quote the Erlang docs for :application.get_env:

If the specified application is not loaded, or if the process executing the call does not belong to any application, the function returns []

In your case, you see nil because given an empty keyword list, Application.get_env is unable to find a key by the name of :forwarder, and so returns nil by default.