Waffle is a Django app that allows developers to include all new features in the master branch while hiding them from users until they are ready. Feature switches allow features to be developed alongside other work in master, with separate deploy and release steps. This prevents features from impacting users until ready and avoids the need for many branching which can be painful and confusing. Switches can be used in templates, JavaScript, views, models and more to selectively show or hide code for a given feature. Care must be taken to ensure all code paths are tested when using feature switches.

1. Waffle
Toby Champion
github.com/tobych
Feature switches for Django

4. Feature branches are nasty
• Must deploy a branch to try things out
• Unlikely to run full tests on a branch
• Many branches: painful and confusing
• Branching inhibits refactoring

5. Feature Switches
Allow you to include all new features on your
master branch, hiding them from users so you
can deploy all your code to production.

6. Now you can hide features!
• Features are developed in master
alongside others
• You have separate deploy and release steps
• Your work need not impact users until ready
• Leave branching just for spikes
• Tests on master run on all features
• Code is more often ready to deploy

7. Let’s use feature switches!

8. Let’s use feature switches!

12. Use your switches everywhere
• Templates
• JavaScript
• Views
• Models
• Jinja2 templates (via Jingo)
• Mustache/Handlebars templates
• Management commands
• Celery tasks

13. {% load waffle_tags %}
{% switch switch_name %}
Switch is active!
{% else %}
Switch is inactive!
{% endswitch %}
Django template

14. Views

15. Wrap an entire view

16. JavaScript

17. Examples

18. Switches
show_replace_button
Show icon for incomplete feature
show_custom_fields
Show custom fields on the edit dialog (delete this switch!)
no_fancy_tag_defaults
Disable broken JavaScript code until we fix it
debug_live
Write extra live update debugging info to JavaScript console
use_reftag_kalman_filtering
Use kalman filtering for reference tag barometer smoothing

19. Flags

20. Flags know about users and groups

21. Examples

22. Flags
show_manage_rules
Show navigation item for new rule manager feature
use_selections
Use new fancy check-box selection instead of drag’n’drop
no_xmpp
Don’t try to contact XMPP (BOSH) server at page load
no_maps
Don’t try to load map tiles at page load

23. Query string
http://example.com/?dwft_my_flag=0 – Off
http://example.com/?dwft_my_flag=1 – On
Persisted for the session using cookies.

24. Also use Waffle for
• A/B testing (Waffle chooses randomly)
• Canary releasing (roll out to % of users)

25. Be careful!
• Even inactive code can break your product
• Unit tests must cover both cases
• Integration tests should cover combinations
• Remove unused switches!
• Harder to follow code wrapped in switches

26. Pain

31. Persistence
• memcached
• Redis

32. Waffle
• http://coffeeonthekeyboard.com/introducing-waffle-for-django-541/
• https://github.com/jsocol/django-waffle
• http://waffle.readthedocs.org/
Feature Switches/Flags/Bits/Toggles
• http://martinfowler.com/bliki/FeatureToggle.html
• http://www.pgrs.net/2011/08/29/why-i-dont-like-feature-branches/
• http://blog.disqus.com/post/789540337/partial-deployment-with-feature-switches
• http://arialdomartini.wordpress.com/2011/11/02/help-me-because-i-think-martin-fowler-has-a-merge-paranoia/
• http://www.youtube.com/watch?v=xzstASOvqNc
• http://codeascraft.com/2011/02/04/how-does-etsy-manage-development-and-operations/
• http://www.infoq.com/presentations/Feature-Bits

33. Toby Champion
@tobych
linkedin.com/in/tobychampion
github.com/tobych/
toby@tobychampion.com

35. Seattle Python Day 2013
• Seattle Python Interest Group (SeaPIG)
• Late September?
• One day (Saturday)
• Free or at least very cheap
• Sprints on the Sunday?