FeatureFlipper

FeatureFlipper is a simple library that allows you to restrict certain blocks of code to certain environments. This is mainly useful in projects where you deploy your application from HEAD and don't use branches.

Install

FeatureFlipper is packaged as a gem:

$ gem install feature_flipper

In your project you have to configure the path to the app specific configuration file after requiring FeatureFlipper:

require 'feature_flipper'
FeatureFlipper::Config.path_to_file = "#{RAILS_ROOT}/config/features.rb"

Configuration

You need to create a configuration file which defines the two entities FeatureFlipper cares about:

states
features

You first define multiple 'states' which normally depend on an environment (for example: the state 'dev' is only active on development boxes). After that you add 'features' which correspond to logical chunks of work in your project. These features then move through the different states as they get developed.

Defining features

A feature needs to have a name and you can add additional information like a more detailed description, a ticket number, a date when it was started, etc. Features are always defined in a state, you cannot define a feature which doesn't belong to a state.

in_status :dev do
  feature :rating_game, :description => 'play a game to get recommendations'
end

Defining states

A state is just a name and a boolean check. The check needs to evaluate to ´true´ when it is active. For a Rails app you can just use environments:

:dev      => ['development', 'test'].include?(Rails.env),

Usage

In your code you then use the show_feature? method to branch depending on wether the feature is active or not:

if show_feature?(:rating_game)
  # new code
else
  # old code
end

The show_feature? method is defined on Object, so you can use it everywhere.

Example config file

FeatureFlipper.features do
  in_status :dev do
    feature :rating_game, :description => 'play a game to get recommendations'
  end

  in_status :live do
    feature :city_feed, :description => 'stream of content for each city'
  end
end

FeatureFlipper::Config.states = {
  :dev      => ['development', 'test'].include?(Rails.env),
  :live     => true
}

This is your complete features.rb config file. In the example there are two states: :dev is active on development boxes and :live is always active (this is the last state a feature is in).

The feature :rating_game is still in development and not shown on the production site. The feature :city_feed is done and already enabled everywhere. You transition features between states by just moving the line to the new state block.

You can take a look at this example in detail in the 'examples' folder.

Cleaning up

The drawback of this approach is that your code can get quite ugly with all these if/else branches. So you have to be strict about removing (we call it de-featurizing) features after they have gone live.

Author

Florian Munz, Qype GmbH - [email protected]