instacart/flip

Flip lets you declare and manage feature flags, backed by cookies (private testing) and database (site-wide).

Flip — flip your features

Flip provides a declarative, layered way of enabling and disabling application functionality at run-time.

This gem optimizes for:

• developer ease-of-use,
• visibility and control for other stakeholders (like marketing); and
• run-time performance

There are three layers of strategies per feature:

• default
• database, to flip features site-wide for all users
• cookie, to flip features just for you (or someone else)

There is also a configurable system-wide default - !Rails.env.production?` works nicely.

Flip has a dashboard UI that's easy to understand and use.

Install

Rails 3.0, 3.1 and 3.2+

# Gemfile
gem "flip"

# Generate the model and migration
> rails g flip:install

# Run the migration
> rake db:migrate

# Include the Feature model, e.g. config/initializers/feature.rb:
require 'feature'

Declaring Features

# This is the model class generated by rails g flip:install
class Feature < ActiveRecord::Base
  extend Flip::Declarable

  # The recommended Flip strategy stack.
  strategy Flip::CookieStrategy
  strategy Flip::DatabaseStrategy
  strategy Flip::DefaultStrategy
  default false

  # A basic feature declaration.
  feature :shiny_things

  # Override the system-wide default.
  feature :world_domination, default: true

  # Enabled half the time..? Sure, we can do that.
  feature :flakey,
    default: proc { rand(2).zero? }

  # Provide a description, normally derived from the feature name.
  feature :something,
    default: true,
    description: "Ability to purchase enrollments in courses"

end

Checking Features

Flip.on? or the dynamic predicate methods are used to check feature state:

Flip.on? :world_domination   # true
Flip.world_domination?       # true

Flip.on? :shiny_things       # false
Flip.shiny_things?           # false

Views and controllers use the feature?(key) method:

<div>
  <% if feature? :world_domination %>
    <%= link_to "Dominate World", world_dominations_path %>
  <% end %>
</div>

Feature Flipping Controllers

The Flip::ControllerFilters module is mixed into the base ApplicationController class. The following controller will respond with 404 Page Not Found to all but the index action unless the :something feature is enabled:

class SampleController < ApplicationController

  require_feature :something, :except => :index

  def show
  end

  def index
  end

end

Dashboard

The dashboard provides visibility and control over the features.

The gem includes some basic styles:

= content_for :stylesheets_head do
  = stylesheet_link_tag "flip"

You probably don't want the dashboard to be public. Here's one way of implementing access control.

app/controllers/admin/features_controller.rb:

class Admin::FeaturesController < Flip::FeaturesController
  before_action :assert_authenticated_as_admin
end

app/controllers/admin/strategies_controller.rb:

class Admin::StrategiesController < Flip::StrategiesController
  before_action :assert_authenticated_as_admin
end

routes.rb:

namespace :admin do
  resources :features, only: [ :index ] do
    resources :strategies, only: [ :update, :destroy ]
  end
end

mount Flip::Engine => "/admin/features"

Cacheable

You can optimize your feature to ensure that it doesn't make a ton of feature calls by adding Cacheable to your model.

extend Flip::Cacheable

This will ensure that your features are eager loaded with one call to the database instead of every call to Flip#on? generating a call to the database. This is helpful if you have a larger Rails application and more than a few features defined.

To start or reset the cache, just call #start_feature_cache.

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Created by Paul Annesley Copyright © 2011-2013 Learnable Pty Ltd, MIT Licence.