Feature Flags¶
Feature flags is a way to have features under development live on production and visible only to admins/beta-users.
The idea of Feature Flags came from Flicker. They manage their development on a single branch using feature flags.
http://code.flickr.com/blog/2009/12/02/flipping-out/
Using Feature Flags¶
Feature flags are used in templates and in controller classes.
To make some part of the template visible only if a feature-flag is enabled:
$if "lists" in ctx.features:
<h3>Lists</h3>
$for list in page.get_lists():
...
To enable a url only if a feature flag is enabled:
class home(delegate.page):
path = "/"
def is_enabled(self):
return "home-v2" in web.ctx.features
def GET(self):
return render_template("home")
Setting Feature Flags¶
In Open Library, the feature flags are specified in the openlibrary.yml file as follows:
features:
merge-authors: enabled
lists: admin
lending_v2:
filter: usergroup
usergroup: beta-users
The value of a feature flag is called a filter. A filter can be specified either as its name or as a dict containing its name and parameters. For example, the following 2 example mean the same.
features:
lists: admin
features:
lists:
filter: admin
Available filters are:
enabled
Enabled for all users.
disabled
Disabled for all users.
loggedin
Enabled only for logged-in users.
admin
Enabled for admin users.
usergroup
Enabled for the users part of the specified usergroup.
lending_v2: filter: usergroup usergroup: beta-users
queryparam
Enabled only if the url has a specified query parameter.
debug: filter: queryparam name: debug value: true