Feature flags in AMY

What are feature flags?

Feature flags are a way to enable or disable features in a software application. They are used to enable gradual rollouts of new features, A/B testing, and to enable or disable features for specific users.

How are feature flags implemented in AMY?

AMY uses the django-flags package to implement feature flags.

How do I add a new feature flag?

Extend FLAGS setting in config/settings.py with a new flag. For example:

FLAGS = {
    "EMAIL_MODULE": [
        {"condition": "anonymous", "value": False, "required": True},
        {"condition": "parameter", "value": "enable_email_module=true"},
        {"condition": "session", "value": "enable_email_module"},
    ],
}

You can read about the different conditions in the django-flags documentation.

How do I use a feature flag in my code?

1. To enable a function based on a feature flag, use the feature_flag_enabled decorator from workshops.utils.feature_flags module.
2. To enable a template block based on a feature flag, use the flag_enabled template tag from django-flags module ({% load feature_flags %}).

EMAIL_MODULE is a good feature flag example that can be tracked in the code to see how it works.

How to use feature flags view to enable or disable a flag?

This view operates on specific conditions set in FLAGS setting in config/settings.py.

First, a parameter condition must be set with a value xyz=true. This will enable the flag for the user if the user visits a URL with ?xyz=true parameter. For example, https://amy.carpentries.org/?xyz=true. However, by default the URL is not persistent, so if the user changes the page to a one without this parameter, the flag will be disabled again. To circumvent this, a special middleware was created that will save the flag parameter in the session if user's request path passes the parameter condition.

When combined with a session condition, such feature flag will stay enabled until the user logs out or uses the "Disable" link.

Disable link is also handled through the special middleware and it only accepts ?xyz=false format.