Typed Runtime configuration for Elixir/Erlang

Distillery's REPLACE_OS_VARS is cool, but it can provide only binary values. This tiny script will cast your runtime, ENV-based configuration to proper values (atoms, integers, booleans).

Have you ever wanted to set the logger level in runtime?

# config/prod.exs
config :logger, level: "${LOG_LEVEL}"

# LOG_LEVEL=warn
iex(hello@127.0.0.1)3> Logger.warn "hello"
** (FunctionClauseError) no function clause matching in Logger.level_to_number/1

    The following arguments were given to Logger.level_to_number/1:

        # 1
        "warn"

Now you can!

# config/prod.exs
config :logger, level: {:atom, "${LOG_LEVEL}"}

# LOG_LEVEL=warn
iex(hello@127.0.0.1)3> Logger.warn "hello"
13:22:25.461 [warn]  hello

Installation

All you need to do is copy a single file, add one line to release config and adjust the prod configuration.

1. Wrap config values in {type, value} tuples

# config/prod.exs
use Mix.Config

config :hello,
  str_var: "${STR_VAR}",
  int_var: {:integer, "${INT_VAR}"},
  bool_var: {:boolean, "${BOOL_VAR}"}

2. Copy typonf.sh into rel/hooks/typonf.sh

# this code snippet is here so you don't miss it
mkdir -p rel/hooks
vim rel/hooks/typonf.sh

3. Set post_configure_hook in rel/config.exs

# rel/config.exs
environment :prod do
  # ...
  set post_configure_hook: "rel/hooks/typonf.sh"
end

4. PROFIT

# build release
mix release

# see it working
STR_VAR=hi INT_VAR=123 BOOL_VAR=true REPLACE_OS_VARS=true _build/prod/rel/hello/bin/hello console
iex(hello@127.0.0.1)1> Application.get_env(:hello, :str_var)
"hi"
iex(hello@127.0.0.1)2> Application.get_env(:hello, :int_var)
123
iex(hello@127.0.0.1)3> Application.get_env(:hello, :bool_var)
true