abstract_feature_branch is a Ruby gem that provides a variation on the Branch by Abstraction Pattern by Paul Hammant and the Feature Toggles Pattern by Martin Fowler (aka Feature Flags) to enable Continuous Integration and Trunk-Based Development.
MIT License
abstract_feature_branch
is a Ruby gem that provides a unique variation on the Branch by Abstraction Pattern by Paul Hammant and the Feature Toggles Pattern by Martin Fowler to enhance team productivity and improve software fault tolerance.
It provides the ability to wrap blocks of code with an abstract feature branch name, and then specify in a configuration file which features to be switched on or off.
The goal is to build out upcoming features in the same source code repository branch (i.e. Continuous Integration and Trunk-Based Development), regardless of whether all are completed by the next release date or not, thus increasing team productivity by preventing integration delays. Developers then disable in-progress features until they are ready to be switched on in production, yet enable them locally and in staging environments for in-progress testing.
This gives developers the added benefit of being able to switch a feature off after release should big problems arise for a high risk feature.
abstract_feature_branch
additionally supports Domain Driven Design's pattern of
Bounded Contexts by allowing developers to configure
context-specific feature files if needed.
abstract_feature_branch
is one of the simplest and most minimalistic "Feature Flags" Ruby gems out there as it enables you to get started very quickly by simply leveraging YAML files without having to set up a data store if you do not need it (albeit, you also have the option to use Redis as a very fast in-memory data store).
~> 3.3.0
and ~> 1.9.1
)~> 7.0
and ~> 2.0
)~> 7.0
and ~> 2.0
)~> 5.0
and ~> 3.0
)rails
between ~> 7.0
and ~> 2.0
: Add the following to Gemfile gem 'abstract_feature_branch', '~> 1.6.0'
rails
~> 2.0
only: Add the following to config/environment.rb config.gem 'abstract_feature_branch', :version => '1.6.0'
~> 7.0
and ~> 3.0
): On the Mac, you can install simply via Homebrew with brew install redis
redis
client gem (between ~> 5.0
and ~> 3.0
): Add the following to Gemfile above abstract_feature_branch
gem 'redis', '~> 5.0.5'
config/features.yml contains the main configuration for the application features.
config/features.local.yml contains local overrides for the configuration, ignored by git, thus useful for temporary local feature switching for development/testing/troubleshooting purposes.
Optional context specific config/features/[context_path].yml contain feature configuration for specific application contexts. For example: admin, public, or even internal/wiki. Useful for better organization especially once config/features.yml grows too big (e.g. 20+ features)
Optional context specific config/features/[context_path].local.yml contain local overrides for context-specific feature configuration. These files are rarely necessary as any feature (even a context feature) can be overridden in config/features.local.yml, so these additional *.local.yml files are only recommended to be utilized once config/features.local.yml grows too big (e.g. 20+ features).
Here are the contents of the generated sample config/features.yml, which you can modify with your own features, each enabled (true) or disabled (false) per environment (e.g. production).
defaults: &defaults feature1: true feature2: true feature3: false feature4: scoped development: <<: *defaults test: <<: *defaults staging: <<: *defaults feature2: false production: <<: *defaults feature1: false feature2: false
Notice in the sample file how the feature "feature1" was configured as true (enabled) by default, but overridden as false (disabled) in production. This is a recommended practice.
multi-line logic:
feature_branch :feature1 do # perform logic end
single-line logic:
feature_branch(:feature1) { # perform logic }
Note that feature_branch returns nil
and does not execute the block if the feature is disabled or non-existent.
feature_branch
supports multi-threaded code (i.e. usage from multiple parallel threads, as possible in JRuby).
if feature_enabled?(:feature1) # perform logic else # perform alternate logic end
Note that feature_enabled? returns false
if the feature is disabled and nil
if the feature is non-existent (practically the same effect, but nil can sometimes be useful to detect if a feature is referenced).
feature_enabled?
supports multi-threaded code (i.e. usage from multiple parallel threads, as possible in JRuby).
AbstractFeatureBranch.environment_features('development') # => {"feature1"=>true, "feature2"=>false, "feature3"=>false, "feature4"=>true}
It is possible to restrict enablement of features per specific users (or per entities of any kind) by setting a feature value to scoped, and then toggling features for specific users (or other entities).
scope = current_user.email AbstractFeatureBranch.toggle_features_for_scope(scope, :feature1 => true, :feature2 => false, :feature3 => true, :feature5 => true)
Use alternate version of feature_branch and feature_enabled? passing extra scope argument
Examples:
feature_branch :feature1, current_user.email do # THIS WILL EXECUTE end
if feature_enabled?(:feature2, current_user.email) # THIS ONE WILL NOT EXECUTE else # THIS ONE WILL EXECUTE end
feature_branch :feature1, another_user.email do # THIS WILL NOT EXECUTE end
if feature_enabled?(:feature2, another_user.email) # THIS ONE WILL EXECUTE (assuming feature2 is enabled in features.yml) else # THIS ONE WILL NOT EXECUTE end
Note:
If a feature is enabled as true or disabled as false in features.yml (or one of the overrides like features.local.yml or environment variable overrides), then it overrides toggled scoped feature restrictions, becoming enabled or disabled globally.
AbstractFeatureBranch.toggle_features_for_scope(scope, feature1: true, feature2: false, ...)
: API method that toggles features (Strings or Symbols) for a scope
AbstractFeatureBranch.toggled_features_for_scope(scope)
: API method that returns toggled features for a scope (String)
AbstractFeatureBranch.scopes_for_feature(feature)
: API method that returns scopes for a (scoped) feature (String or Symbol)
feature_branch :add_business_project do resources :projects end
<% feature_branch :add_business_project do %> <h2>Submit a Business</h2> <p> Please submit a business idea for review. </p> <ul> <% current_user.projects.each do |p| %> <li><%= link_to p.business_campaign_name, project_path(p) %></li> <% end %> </ul> <h4> <%= link_to('Start', new_project_path, :id => "business_background_invitation", :class => 'button') %> </h4> <% end %>
params.require(:project).permit( feature_branch(:project_gallery) {:exclude_display}, :name, :description, :website )
<% feature_branch :project_gallery do %> .exclude_display { margin-left: auto; margin-right: auto; label { font-size: 1em; text-align: center; } height: 47px; } <% end %> label { font-size: 1.5em; margin-bottom: -15px; margin-top: 3px; display: inline; }
Once a feature has been released and switched on in production, and it has worked well for a while (e.g. for two consecutive releases), it is strongly recommended that its feature branching code is plucked out of the codebase to simplify and improve future maintainability given that it is no longer needed at that point.
Once config/features.yml grows too big (e.g. 20+ features), it is strongly recommended to split it into multiple context-specific feature files by utilizing the context generator mentioned above: rails g abstract_feature_branch:context context_path
When working on a new feature locally that the developer does not want others on the team to see yet, the feature can be enabled in config/features.local.yml only as it is git ignored while the feature is disabled in config/features.yml
When troubleshooting a deployed feature by simulating a non-development environment (e.g. staging or production) locally, the developer can disable it temporarily in config/features.local.yml (git ignored) under the non-development environment, perform tests on the feature, and then remove the local configuration once done.
You can override feature configuration with environment variables by setting an environment variable with a name matching this convention (case-insensitive): ABSTRACT_FEATURE_BRANCH_[feature_name] and giving it the case-insensitive value "TRUE" or "FALSE"
Example:
export ABSTRACT_FEATURE_BRANCH_FEATURE1=TRUE rails s
The first command adds an environment variable override for feature1 that enables it regardless of any feature configuration, and the second command starts the rails server with feature1 enabled.
To remove an environment variable override, you may run:
unset ABSTRACT_FEATURE_BRANCH_FEATURE1 rails s
The benefits can be achieved more easily via config/features.local.yml mentioned above. However, environment variable overrides are implemented to support overriding feature configuration for a Heroku deployed application more easily.
Prerequisites: Redis server and client (redis
gem) and Redis configuration of AbstractFeatureBranch.feature_store
in config/initializers/abstract_feature_branch.rb
(Redis
ConnectionPool
instance is recommended for Production environments)
To be able to override feature configuration in a production environment, you can utilize Redis Overrides.
Alternatively, you may use Redis Overrides as your main source of feature configuration if you prefer that instead of relying on YAML files.
Keep in mind that by default, Redis Overrides are fetched on app/server start to pre-cache for better performance.
To enable live fetching of Redis Overrides, set AbstractFeatureBranch#feature_store_live_fetching
to true
(e.g. in config/initializers/abstract_feature_branch.rb
), but keep in mind the trade-off with more latency due to making calls to Redis Server over the network.
You can override feature configuration with Redis hash values by calling AbstractFeatureBranch#set_store_feature
in rails console
(or irb
after requiring redis
and abstract_feature_branch
):
AbstractFeatureBranch.set_store_feature('feature1', true)
Behind the scenes, that is the equivalent of the following Redis client invocation, which stores a hash value in a 'abstract_feature_branch'
key:
AbstractFeatureBranch.configuration.feature_store.hset('abstract_feature_branch', 'feature1', 'true')
To remove a Redis override, you can run the following in rails console
(or irb
):
AbstractFeatureBranch.delete_store_feature('feature1')
To get a Redis override value, you can run the following in rails console
(or irb
):
AbstractFeatureBranch.get_store_feature('feature1')
To get an array of all Redis Override features, you can run the following in rails console
(or irb
):
AbstractFeatureBranch.get_store_features
Environment variable overrides can be extremely helpful on Heroku as they allow developers to enable/disable features at runtime without a redeploy.
Enabling a new feature without a redeploy:
Disabling a buggy recently deployed feature without a redeploy:
Removing an environment variable override:
It is recommended that you use environment variable overrides on Heroku only as an emergency or temporary measure. Afterward, make the change official in config/features.yml, deploy, and remove the environment variable override for the long term.
If you've used abstract feature branching in CSS or JS files via ERB, setting environment variable overrides won't affect them as you need asset recompilation in addition to it, which can only be triggered by changing a CSS or JS file and redeploying on Heroku (even if it's just a minor change to force it). In any case, environment variable overrides have been recommended above as an emergency or temporary measure. If there is a need to rely on environment variable overrides to alter the style or JavaScript behavior of a page back and forth without a redeploy, one solution is to do additional abstract feature branching in HTML templates (e.g. ERB or HAML to link to different stylesheets and JS files, use different CSS classes, or invoke different JavaScript methods per branch of HTML for example.)
For better knowledge and clarity, here is the order in which feature configuration is loaded, with the latter sources overriding the former if overlap in features occurs:
Here is the content of the generated initializer [with redis
client gem added] (config/initializers/abstract_feature_branch.rb), which contains instructions on how to customize via dependency injection:
# Storage system for features (other than YAML/Env-Vars). Right now, only Redis and ConnectionPool are supported. # AbstractFeatureBranch.feature_store = Redis.new # Storage can be a Redis ConnectionPool instance # AbstractFeatureBranch.feature_store = ConnectionPool.new { Redis.new } # The following example line works with Heroku Redis To Go while still operating on local Redis for local development # AbstractFeatureBranch.feature_store = Redis.new(:url => ENV['REDISTOGO_URL']) # Enable live fetching of feature configuration from storage system, to update features without app/server restart. # false by default to only load features on app/server start for faster performance (requires restart on change) AbstractFeatureBranch.feature_store_live_fetching = false # Application root where config/features.yml or config/features/ is found AbstractFeatureBranch.application_root = Rails.root # Application environment (e.g. "development", "staging" or "production") AbstractFeatureBranch.application_environment = Rails.env.to_s # Abstract Feature Branch logger AbstractFeatureBranch.logger = Rails.logger # Cache feature files once read or re-read them at runtime on every use (helps development). # Defaults to true if environment not specified, except for development, which defaults to false. AbstractFeatureBranch.cacheable = { :development => false, :test => true, :staging => true, :production => true } # Pre-load application features to improve performance of first web-page hit AbstractFeatureBranch.load_application_features unless Rails.env.development?
Abstract Feature Branch comes with a rake task to beautify feature files that have grown unorganized by sorting features by name and getting rid of extra empty lines. It does so per section, without affecting the order of the sections themselves.
For example, here is content before and after beautification.
Before:
defaults: &defaults gallery: true carousel: true third_party_integration: false caching: true development: <<: *defaults test: <<: *defaults caching: false staging: <<: *defaults third_party_integration: true caching: true production: <<: *defaults third_party_integration: false caching: false
After:
defaults: &defaults caching: true carousel: true gallery: true third_party_integration: false development: <<: *defaults test: <<: *defaults caching: false staging: <<: *defaults caching: true third_party_integration: true production: <<: *defaults caching: false third_party_integration: false
This is very useful in bigger applications that have scores of features since it allows a developer to quickly scan for alphabetical sorted feature names. Although file find is an alternative solution, having tidy organized feature names can help increase overall team productivity in the long term.
For Rails application use, the rake task is generated under lib/tasks/abstract_feature_branch.rake.
For Ruby application general use, here is the content of the rake task:
require 'abstract_feature_branch' namespace :abstract_feature_branch do desc "Beautify YAML of specified feature file via file_path argument or all feature files when no argument specified (config/features.yml, config/features.local.yml, and config/features/**/*.yml) by sorting features by name and eliminating extra empty lines" task :beautify_files, :file_path do |_, args| AbstractFeatureBranch::FileBeautifier.process(args[:file_path]) end end
The rake task may be invoked in a number of ways:
Note that the beautifier ignores comments at the top, but deletes entire line comments in the middle of a YAML file, so after invoking the rake task, verify that your feature file contents are to your satisfaction before committing the task changes.
Although feature branches and branching by abstraction are similar, there are different situations that recommend each approach.
Feature branching leverages your version control software (VCS) to create a branch that is independent of your main branch. Once you write your feature, you integrate it with the rest of your code base. Feature branching is ideal for developing features that can be completed within the one or two iterations. But it can become cumbersome with larger features due to the fact your code is isolated and quickly falls out of sync with your main branch. You will have to regularly rebase with your main branch or devote substantial time to resolving merge conflicts.
Branching by abstraction, on the other hand, is ideal for substantial features, i.e. ones which take many iterations to complete. This approach to branching takes place outside of your VCS. Instead, you build your feature, but wrap the code inside configurable flags. These configuration flags will allow for different behavior, depending on the runtime environment. For example, a feature would be set to "on" when your app runs in development mode, but "off" when running in "production" mode. This approach avoids the pain of constantly rebasing or resolving a myriad of merge conflicts when you do attempt to integrate your feature into the larger app.
Copyright (c) 2012-2023 Andy Maleh. See LICENSE.txt for further details.