Exconfig

Context

Don't use ENV-settings for compile-time configuration. (Because it is hard to maintain your environment-settings for different deployments.

Imagine you want to build a Docker-image for your Phoenix-application and you use something like

   plug SomePlug, config_value: System.get_env("SOME_KEY")

plug is a macro and therefore, SOME_KEY gets evaluated at compile time. If SOME_KEY is customer-related, this setting get's burned into the image and may surprisingly pop up at the wrong customer's server.

The Exconfig-package will help you not to make this mistake. Just use Exconfig.get instead of all your Application.get_env and System.get_env calls. Because the cache-server of Exconfig will not run at compile-time you'll get a compile-error if you try to use System-envs from your busines-logic.

Usage

The application starts a GenServer and caches configuration at run time.

Loading configuration happens in two steps where each step overwrites eventually existing values from previous steps.

Application.get_env(:app, :key) default
System.get_env(:key) default

Once the value is cached it will be returned from the GenServer state rather than re-reading it from the environment again.

Using Exconfig.clear_cache!/0 will drop the cache and values will be loaded again if being accessed later.

Example:

iex> value = Exconfig.get(:my_app, :foo, "bar" )
"bar"

iex> value = Exconfig.get(:env, :some_secret )
nil

Exconfig.get/3 will first lookup for :myapp/:foo in the Exconfig.Cache (a GenServer) and if not found load from Application, System, or returns the default. The second example will read from env-var SOME_SECRET. Because no default value is given, it will return nil

configuration.log

Exconfig.get/3 is a macro. At compile-time in any environment but :prod, it will capture it's usage in a file. The file can be configured in config.ex and defaults to configuration.log.

The File can be used as a template for a shell-script.

Installation

Available in Hex. The package can be installed by adding Exconfig to your list of dependencies in mix.exs:

def deps do
  [
    {:exconfig, "~> 0.2.0"}
  ]
end