5.6 KiB
Developing with feature flags
In general, it's better to have a group- or user-based gate, and you should prefer
it over the use of percentage gates. This would make debugging easier, as you
filter for example logs and errors based on actors too. Furthermore, this allows
for enabling for the gitlab-org
or gitlab-com
group first, while the rest of
the users aren't impacted.
# Good
Feature.enabled?(:feature_flag, project)
# Avoid, if possible
Feature.enabled?(:feature_flag)
To use feature gates based on actors, the model needs to respond to
flipper_id
. For example, to enable for the Foo model:
class Foo < ActiveRecord::Base
include FeatureGate
end
Features that are developed and are intended to be merged behind a feature flag should not include a changelog entry. The entry should either be added in the merge request removing the feature flag or the merge request where the default value of the feature flag is set to true. If the feature contains any DB migration it should include a changelog entry for DB changes.
In the rare case that you need the feature flag to be on automatically, use
default_enabled: true
when checking:
Feature.enabled?(:feature_flag, project, default_enabled: true)
The Project#feature_available?
,
Namespace#feature_available?
(EE), and
License.feature_available?
(EE) methods all implicitly check for
a by default enabled feature flag with the same name as the provided argument.
For example if a feature is license-gated, there's no need to add an additional
explicit feature flag check since the flag will be checked as part of the
License.feature_available?
call. Similarly, there's no need to "clean up" a
feature flag once the feature has reached general availability.
You'd still want to use an explicit Feature.enabled?
check if your new feature
isn't gated by a License or Plan.
An important side-effect of the implicit feature flags mentioned above is that
unless the feature is explicitly disabled or limited to a percentage of users,
the feature flag check will default to true
.
This is relevant when developing the feature using several smaller merge requests, or when the feature is considered to be an alpha or beta, and should not be available by default.
As an example, if you were to ship the frontend half of a feature without the
backend, you'd want to disable the feature entirely until the backend half is
also ready to be shipped. To make sure this feature is disabled for both
GitLab.com and self-managed instances, you should use the
Namespace#alpha_feature_available?
or
Namespace#beta_feature_available?
method, according to our definitions. This ensures the feature is disabled unless the feature flag is
explicitly enabled.
Feature groups
Starting from GitLab 9.4 we support feature groups via Flipper groups.
Feature groups must be defined statically in lib/feature.rb
(in the
.register_feature_groups
method), but their implementation can obviously be
dynamic (querying the DB etc.).
Once defined in lib/feature.rb
, you will be able to activate a
feature for a given feature group via the feature_group
parameter of the features API
Frontend
For frontend code you can use the method push_frontend_feature_flag
, which is
available to all controllers that inherit from ApplicationController
. Using
this method you can expose the state of a feature flag as follows:
before_action do
push_frontend_feature_flag(:vim_bindings)
end
def index
# ...
end
def edit
# ...
end
You can then check for the state of the feature flag in JavaScript as follows:
if ( gon.features.vimBindings ) {
// ...
}
The name of the feature flag in JavaScript will always be camelCased, meaning
that checking for gon.features.vim_bindings
would not work.
See the Vue guide for details about how to access feature flags in a Vue component.
Specs
In the test environment Feature.enabled?
is stubbed to always respond to true
,
so we make sure behavior under feature flag doesn't go untested in some non-specific
contexts.
Whenever a feature flag is present, make sure to test both states of the feature flag.
See the testing guide for information and examples on how to stub feature flags in tests.
Enabling a feature flag (in development)
In the rails console (rails c
), enter the following command to enable your feature flag
Feature.enable(:feature_flag_name)
Similarly, the following command will disable a feature flag:
Feature.disable(:feature_flag_name)