Elixir configuration provider inspired by Haskell programming experience. Runtime configuration of Haskell programs is a bit different if we compare with other languages like Elixir. Haskell program business logic mainly contains pure functions which can call only pure functions by their nature. This means that in random place of Haskell program something like Elixir function Application.get_env/2
or System.get_env/1
can't be called at all (because these functions are not pure). As a result of this, in Haskell programs all needed runtime configurations are usually fetched, transformed and validated during initial boot process of program, and after this passed to main loop function as arguments (typed values).
- configuration parameters have a schema
- configuration parameters are validated during boot process according schema
- if runtime configuration is incorrect then application will crash on boot (it's much better than runtime errors in random moment of time)
get_env/1
expressions have compile-time guarantees of correctness according given schema- configuration parameters are stored in ETS table, so fetching by key is super fast
Define configuration schema in dedicated module:
- define namespaces with
conf/2
expressions - multiple
conf/2
expressions are supported conf/2
expressions can be nested- define configuration parameters with
env/2
expressions - do-block of
env/2
expression is boolean expression (parameter validation code)
defmodule MyApp.BootEnv do
use BootEnv
conf :my_app do
env ecto_repos, do: is_list(ecto_repos)
env logo_url, do: Regex.match?(~r/^https?\:\/\/.+$/, logo_url)
env backoffice_pagination do
is_integer(backoffice_pagination) and
backoffice_pagination > 0
end
conf MyApp.Repo do
env username, do: String.valid?(username)
env password, do: String.valid?(password)
env database, do: String.valid?(database)
env hostname, do: String.valid?(hostname)
env pool_size, do: is_integer(pool_size) and pool_size > 1
end
end
end
Start configuration provider as first child in supervision tree:
children =
[
# Start BootEnv configuration first
MyApp.BootEnv,
# Start the Ecto repository
MyApp.Repo
# ...
]
Fetch runtime configuration parameter with get_env/1
expression where it's needed:
require MyApp.BootEnv, as: Conf
img_tag(Conf.get_env([:my_app, :logo_url]), class: "image")
#=> <img src="https://foo.bar/img/smile.png" class="image">
The package can be installed by adding boot_env
to your list of dependencies in mix.exs
:
def deps do
[
{:boot_env, "~> 0.1.1"}
]
end
I very recommend to combine this tool with ExEnv.