README

SimpleFeatureFlags provides a simple way to enable or disable features, per-environment, using application configuration.

Installation

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

def deps do
  [
    {:simple_feature_flags, "~> 0.1"}
  ]
end

The docs can be found at https://hexdocs.pm/simple_feature_flags.

Code Example

Configuration

Determine the name of the deployment environment you are running in, and list the environments in which your feature is enabled.

In this example, the name of the deployment environment is loaded from an environment variable, and the new_algorithm feature is enabled in localhost and staging:

config/runtime.exs

current_deployment_environment =
  System.get_env("DEPLOYMENT_ENVIRONMENT")
  |> case do
    nil -> raise "DEPLOYMENT_ENVIRONMENT is not defined"
    env -> String.to_atom(env)
  end


config :simple_feature_flags, :flags, %{
  current_deployment_environment: current_deployment_environment,
  features: %{
    new_algorithm: %{enabled_in: [:localhost, :staging]},
    new_ui: %{enabled_in: [:staging]}
  }
}

Using Feature Flag in Your Code

Wrap your feature logic in SimpleFeatureFlags.enabled?/1:

def compute_pi() do
  if SimpleFeatureFlags.enabled?(:new_algorithm) do
    # Use the new, better algorithm.
    compute_pi_new_algorithm()
  else
    # Use the old, boring algorithm.
    3.14
  end
end

Optional: Log Configuration on Startup

lib/myapp/application.ex

defmodule MyApp.Application do

  require Logger
  use Application

  @impl true
  def start(_type, _args) do
    Logger.info(SimpleFeatureFlags.current_configuration_to_string())
    ...

Here is an example of the output:

  Current Deployment Environment: :localhost
  Features:
  - new_algorithm is ON. Enabled in [:localhost, :staging]
  - new_ui is OFF. Enabled in [:staging]