Casconf

Casconf allows you to setup cascading configuration loading.

Basic usage

Consider this example matrix:

config value	default	environment variable	file
endpoint port	4000	HTTP_PORT	N/A
access password	nil	BASIC_AUTH_PASSWORD	/var/local/my_app/basic_auth

In Casconf, you could express it like this in your config.exs:

config :app, Server,
  port: {:casconf, :integer, default: 4000, env: "HTTP_PORT"},
  basic_auth: {:casconf, default: nil, env: "BASIC_AUTH_PASSWORD", file: "/var/local/my_app/basic_auth"}

additionally, the order in which to load the sources can be configured like this:

config :casconf, Casconf.Loader,
  sources: [
    file: Casconf.Loader.File,
    env: Casconf.Loader.Env,
    default: Casconf.Loader.Default
  ]

Now Casconf will try to load the configuration values from the configured sources in the order that was defined in the Casconf.Loader config.

That means that if a file source is given and the file exists, it will be used over an environment variable, which in turn will be tried before falling back on the default.

In your application, load the configuration with either Casconf.get_env or Casconf.Loader.load_in, depending on the way certain modules are configured.

When a library offers an init callback which already took the configuration from Application.get_env (like how Ecto and Phoenix do it), you can implement the init callbacks in this fashion:

defmodule App.Repo do
  use Ecto.Repo, otp_app: :app

  def init(_type, config) do
    config = Casconf.Loader.load_in(config)
    # maybe update some other settings here
    {:ok, config}
  end
end

Otherwise, use Casconf.get_env:

server_config = Casconf.get_env(:app, Server)

Features

• Cascading

  Config sources will be tried in a configurable order

• Type casting

  All types using the Ecto.Type behaviour are supported, as well as the builtin ecto types

• Extensible

  Casconf.Loader is a behaviour you can implement when you need a different configuration source, for example a YAML file, or a database table.

  As Ecto.Type is used for casting the read values into the correct data types, custom types can also be used.

Installation

If available in Hex, the package can be installed by adding casconf to your list of dependencies in mix.exs:

def deps do
  [
    {:casconf, "~> 0.1.0"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/casconf.