Feature toggles allow modifying system behavior without changing code. They can be used to hide unfinished features, limit access to features, gracefully degrade systems under high load, and perform A/B testing. Feature toggles are categorized based on how long they live and how dynamic the toggling decision is. They include release toggles for incomplete code, experiment toggles for A/B testing, ops toggles for performance, and permissioning toggles for access control. Feature toggle libraries like Rollout make it easy to activate, deactivate, and manage feature toggles for different users, groups, or percentages of users.

1. Feature Toggles
BinLi
@holysoros

2. A feature takes longer than
a release cycle?

3. Feature Branch

4. A successful Git branching model

5. But,
• merging long-lived branch is pain;
• continuous integration, if you have…

6. 3 days before deadline,
1395 conflicts found after you execute
‘git merge dev master’

7. Feature Toggles
Allowing to modify system behavior without changing code
• Unfinished feature hide from public;
• Features only be access to VIP users;
• Elegant degrade;

8. Imagine,
you are responsible for developing a new ship
cost algorithm
meanwhile teammates work on same codebase
A Story

9. def evaluateShipCost
if featureEnabled?(‘use-new-ship-cost-algorithm’, current_user)
return newShipCostEvaluator(order)
else
return oldShipCostEvaluator(order)
end
end
The Birth of Feature Toggle

10. Manual exploratory testing
•Internal testing
Canary release
•select 1% users, track business metrics;
A/B Testing
•PM is quite excited to learn about this approach
Other Benefits

11. Categories of toggles
Feature toggles can be categorized across two
major dimensions:
- how long the feature toggle will live
- how dynamic the toggling decision must be

12. Release Toggle
Continuous Delivery principle of "separating [feature] release from [code] deployment.”
Release toggles allow incomplete and un-tested codepaths to be shipped to production

13. Release Toggle
Release!!

14. Experiment Toggles
Experiment Toggles are used to perform A/B testing.
- highly dynamic, must take current user into account; and same collection of users;
- time depends on traffic pattern;

15. Ops Toggles
Be used to control operational aspects of our system's behavior
- rolling out a new feature which has unclear performance implications;
- elegant degrade when system is suffering high load;

16. Permissioning Toggles
- premium features only for VIP;
- beta features only for beta users;

17. Our Examples
• Use Qiniu as paperclip filestore;
• Rollout new products search architecture and
property filters feature;
• New web design;
• New payment method for VIP customers;

18. Implementation

19. Rollout
Feature flippers.
require 'redis'
$redis = Redis.new
$rollout = Rollout.new($redis)
# Check whether a feature is active for a particular user:
$rollout.active?(:chat, User.first)
# Check whether a feature is active globally:
$rollout.active?(:chat)

20. Rollout cont.
# activate globally
$rollout.activate(:chat)
# rollout ship a default group :all, you can define custom groups
# activate specific group
$rollout.activate_group(:chat, :all)
# activate specific users
$rollout.activate_user(:chat, @user)
# activate user percentages
$rollout.activate_percentage(:chat, 20)

21. Thin Abstract
module FeatureDecision
def self.active?(*args)
(!feature_toggle_enabled?) || $rollout.active?(*args) rescue true
end
def self.feature_toggle_enabled?
Rails.env.production? || Rails.env.staging?
end
end
# Use like this
if FeatureDecision.active?(‘new-ship-cost-algorithm’)

22. Where to Place Toggle Point
• Toggles at the edge
• Any place support conditional statement: views,
initializers, model validation etc.

23. Manage Feature Toggles
• Feature Toggles have a tendency to multiply
rapidly, particularly when first introduced.
• A team must be proactive in removing feature
toggles that are no longer needed.
Rule: remove the feature toggle in the next sprint
after release the feature;

24. Branch Strategy
• We have only master branch in origin;
• But, feature toggles may cooperate with branch;

25. Related Components
• rollout_dashboard is a beautiful interactive user
interface for rollout gem.
• degrade keep track of service error rates and
degrade functionality if they're too high.

26. Problems
• Feature toggles for SPA and iOS/Android app?

27. References
• http://martinfowler.com/articles/feature-toggles.html
• http://martinfowler.com/bliki/FeatureToggle.html
• https://github.com/fetlife/rollout
• https://www.infoq.com/news/2016/02/featuretoggles
• https://www.infoq.com/presentations/Facebook-Release-
Process
• https://secure.phabricator.com/book/phabflavor/article/
recommendations_on_branching/