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Feature Flags

Feature flags are a mechanism to customize or hide behavior until enabled explicitly.
The FeatureFlag system is built on the environment Config system and adds features such as
  1. 1.
    Cleaner less error-prone code.
  2. 2.
    Manual overrides in non prod environments.
  3. 3.
    Ability to write browser tests.
Currently we only have boolean flags/support but others could be added as necessary.

Uses

Feature flags can be used to control features that will always be configuration controled such as if Global Admins are also Program Admins. The code, tests and configuration will always be present in CiviForm.
Feature flags can also be used as launch gating controls for features that can't be done in a single PR. This allows you to safely do incremental development while your code is being shipped weekly in releases. And then to "launch" it when all is done.

Using

The FeatureFlags class provides readable accessors for environment variables and when a Request object is provided it allows for manual overrides.
Adding a new flag involves
  1. 1.
    Add the Config value to all relevant .conf files.
  2. 2.
    Added accessors in FeatureFlags.
  3. 3.
    Inject FeatureFlags into client classes.
  4. 4.
    Use accessors to vary behavior.

Manual overrides

Overrides are meant for evaluation and development purposes and not production usage.
They and are done through the browser and apply to the current user session only.

Enable

To enable the ability to override all the following must be true:
  1. 1.
    Enable feature_flag_overrides_enabled in the environment configuration.
  2. 2.
    Use a dev or staging server.
  3. 3.
    Are a Global or Program admin.

Access

Boolean flags can be enabled or disabled via url and persist for the browser session.
  • /dev/feature/feature_flag_name/enable
  • /dev/feature/feature_flag_name/disable
For example: /dev/feature/application_status_tracking_enabled/enable enables the status tracking feature for the current user.
The current state of Overrides can be viewed at /dev/feature

Testing

Junit

There are two ways to test Feature Flag conditioned code.
Mock
Create a Mock of FeatureFlags and create a new instance of the class under test passing your mock to it. You can then mock the accessor return values as needed. They're boolean=false by default.
Note this will require manually injecting all its other dependencies via instanceOf().
Creating providers (for DateTime things) is different and looks like Providers.of(LocalDateTime.now(ZoneId.systemDefault())
Request config
Use the override functionality of FeatureFlags and set the session data of your fake requests.
Helpers.fakeRequest().session(FeatureFlags.APPLICATION_STATUS_TRACKING_ENABLED, "false")

Browser

Browser tests use the url override mechanism, which means the feature implementation must also use the http Request for any paths that you test.
This can be done by using the enableFeatureFlag(page, flagName) method in index.ts in your tests.

Probers

Browser tests are overloaded in their usage and are also used as deployment "probers" in various environments including CiviForm ran Staging servers as well Civic Entity ones, this means the default state of feature flags and flagged code in browser tests can not be assumed and must be explicitly set and managed.
For instance CiviForm staging might enable the feature while Seattle Staging does not. When you add the flagged java code you may then get different results in the existing tests until you also update them.

Best Practices

  1. 1.
    Always guard DB write code, even if a path can't be reached unless upstream guarded code was enabled.
  2. 2.
    Consider what will happen if your flag is enabled for some time then disabled. Should data views still be accessible? etc.
  3. 3.
    Always test code with your feature off and on, or other variations. Our dev environments make it easy to only see the bleeding-edge of features, but real users will be seeing the stable released version of your code.