Flags are the most robust, flexible method of rolling out a feature with Waffle. Flags can be used to enable a feature for specific users, groups, users meeting certain criteria (such as being authenticated, or superusers) or a certain percentage of visitors.
How Flags Work¶
Flags compare the current request to their criteria to decide whether they are active. Consider this simple example:
if flag_is_active(request, 'foo'): pass
The flag_is_active function takes two arguments, the
request, and the name of a flag. Assuming this flag (
foo) is defined
in the database, Waffle will make roughly the following decisions:
WAFFLE_OVERRIDEactive and if so does this request specify a value for this flag? If so, use that value.
- If not, is the flag set to globally on or off (the Everyone setting)? If so, use that value.
- If not, is the flag in Testing mode, and does the request specify a value for this flag? If so, use that value and set a testing cookie.
- If not, does the current user meet any of our criteria? If so, the flag is active.
- If not, does the user have an existing cookie set for this flag? If so, use that value.
- If not, randomly assign a value for this user based on the Percentage and set a cookie.
|Name:||The name of the flag. Will be used to identify the flag everywhere.|
|Everyone:||Globally set the Flag, overriding all other criteria. Leave as Unknown to use other critera.|
|Testing:||Can the flag be specified via a querystring parameter? See below <types-flag-testing.|
|Percent:||A percentage of users for whom the flag will be active, if no other criteria applies to them.|
|Superusers:||Is this flag always active for superusers?|
|Staff:||Is this flag always active for staff?|
|Authenticated:||Is this flag always active for authenticated users?|
|Groups:||A list of group IDs for which this flag will always be active.|
|Users:||A list of user IDs for which this flag will always be active.|
|Rollout:||Activate Rollout mode? See below.|
|Note:||Describe where the flag is used.|
A Flag will be active if any of the criteria are true for the current
user or request (i.e. they are combined with
or). For example, if a
Flag is active for superusers, a specific group, and 12% of visitors,
then it will be active if the current user is a superuser or if they
are in the group or if they are in the 12%.
Users are assigned randomly when using Percentages, so in practice the actual proportion of users for whom the Flag is active will probably differ slightly from the Percentage value.
When a Flag is activated by chance, Waffle sets a cookie so the flag will not flip back and forth on subsequent visits. This can present a problem for gradually deploying new features: users can get “stuck” with the Flag turned off, even as the percentage increases.
Rollout mode addresses this by changing the TTL of “off” cookies. When Rollout mode is active, cookies setting the Flag to “off” are session cookies, while those setting the Flag to “on” are still controlled by WAFFLE_MAX_AGE.
Effectively, Rollout mode changes the Percentage from “percentage of visitors” to “percent chance that the Flag will be activated per visit.”