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Feature toggle LEGACY

This page documents the deprecated ENV-based feature toggle API. New feature toggles should use the current Feature toggles guide and EasyFeature.enabled?.

Feature toggler is a mechanism that allows you to enable or disable certain features in your application without changing the code. This is useful when you want to disable some feature that is not ready for production.

Our internal guidelines prefer and support delivering small increments into the codebase to avoid huge merge requests. This could possibly come into the conflict with the release of the current state of code including incomplete feature.

Feature toggler should help to avoid this kind of situation.

Easy Feature Toggle

Easy Feature Toggler is a simple feature toggler that allows you to enable or disable features in our application. You can find it as a module EasyFeatureLegacy located in easy_lib/easy_features/easy_feature_legacy.rb and exposed through the deprecated EasyFeature.active? API. It is based on using ENV variables and represents a way to generalize manipulation with these variables in one place.

Principles are very simple. Module contains one public method active?. This method accepts one argument - ENV variable name. This name is verified, that it matches settled naming convention, during the method process. If the name has incorrect form it will raise argument error. If the name fits the convention, method will return true or false based on the value, false when it's not defined.

During the process of the method, it will also record currently active features into the list, that can be used for future debugging.

Usage

Recommended way to use this module is in engine/plugin module definition, like my_engine/lib/my_engine.rb, which should contain a method corresponding to feature name with active? suffix, e.g.: my_feature_active?.

This module can also be used straight in the code, but with long feature names it could be distracting and unpleasant to read. So it is not recommended.

Expected values for each ENV variable are either true or 1 for active state. Empty value or any other string will result in inactive state.

Feature toggler is not adapted for development environment. It is recommended to take care of this case in methods defined within engine/plugin module.

engine module
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module MyEngine
  class << self
    def my_feature_active?
      return true if Rails.env.development?

      EasyFeature.active?("EASY_FEATURE_MY_FEATURE_ACTIVE")
    end
  end

end
usage in code
class MyFeatureController < ApplicationController
  before_action :check_feature

  # ...

  private

  def check_feature
    render_404 unless MyEngine.my_feature_active?

    # possible usage (not recommended)
    # render_404 unless EasyFeature.active?("EASY_FEATURE_MY_FEATURE_ACTIVE")
  end
end

Naming convention

Input for this feature toggler should ALWAYS be String. It should start with EASY_FEATURE_ prefix followed by feature name in uppercase and underscored format. This name should be followed by _ACTIVE suffix.

Example of correct name: EASY_FEATURE_MY_EASY_FEATURE_ACTIVE.

  def check_if_feature_name_valid?(name)
    raise ArgumentError, "Feature name `#{name}` must be String." unless name.is_a?(String)
    raise ArgumentError, "Feature name must start with `EASY_FEATURE_`." unless name.start_with?("EASY_FEATURE_")
    raise ArgumentError, "Feature name must end with `_ACTIVE`." unless name.end_with?("_ACTIVE")

    true
  end