common-nighthawk/this_feature

Feature Flag wrapper gem

ThisFeature

A common interface to interact with many feature flag providers.

ThisFeature can be used to more easily migrate from one feature flag service to another

If your code uses ThisFeature, then you can just swap out the vendor adapter without needing to do a bunch of find-and-replace in your codebase from one vendor's class/method signature to the another's.

Installation

Add ThisFeature to your Gemfile:

# Gemfile
gem 'this_feature'

Then from your Rails app's root directory:

bundle install

Configuration

# config/initializers/this_feature.rb
require 'this_feature'
require 'this_feature/adapters/memory'

ThisFeature.configure do |config|
  adapter = ThisFeature::Adapters::Memory.new
  config.adapters = [adapter]
  config.default_adapter = adapter
end

NOTE: When searching for the presence of a flag, adapters are queried in order. The default adapter is the fallback adapter used when a flag isn't present in any of the adapters.

Usage

Flags

ThisFeature.flag('flag_name').on?      # is the flag is turned on?
ThisFeature.flag('flag_name').off?     # is the flag is turned off?
ThisFeature.flag('flag_name').control? # is the adapter using the control?
ThisFeature.default_adapter            # access the default adapter directly if needed

Context

You can also pass a context to the flag, many feature flagging systems support this.

ThisFeature.flag('flag_name', context: current_user).on?

Data

In case context is not sufficient, you can also pass a data hash.

ThisFeature.flag('flag_name', context: context, data: { org_id: 1 }).on?

Avoid Pitfalls

1. If your flag has context-specific rules (e.g. on for some orgs, off for others), make sure that the code does a context-specific check. ThisFeature.flag("flag_name").on? may return true, while ThisFeature.flag("flag_name", context: Org.first).on? would return false.
2. Related to the previous bullet point, if you are checking whether a flag is "globally enabled" (and thus may be removed from the codebase), do not just use ThisFeature.flag("flag_name").on?, it won't tell you the whole story. Go to the vendor console and check whether there are context-specific rules enabled.

Available Adapters

These adapters do behave slightly differently, so make sure to read the following docs:

• Flipper adapter
• Split.io adapter
• Memory adapter - designed for use in tests

Needed Adapters

We'd like to add more adapters for more vendors. If you're using a different backend and write your own adapter, please submit a pull request to upstream that adaptor into this repo.

• Launch Darkly
• YAML files
• ...

Development

The tests are a good reflection of the current development state. You can run the tests with these commands in your Terminal:

bundle install && bundle exec rspec

To write a new adapter, check the Guide.

License

ThisFeature is released under the MIT License.