141 lines
5.5 KiB
Markdown
141 lines
5.5 KiB
Markdown
# Developing with feature flags
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In general, it's better to have a group- or user-based gate, and you should prefer
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it over the use of percentage gates. This would make debugging easier, as you
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filter for example logs and errors based on actors too. Furthermore, this allows
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for enabling for the `gitlab-org` or `gitlab-com` group first, while the rest of
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the users aren't impacted.
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```ruby
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# Good
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Feature.enabled?(:feature_flag, project)
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# Avoid, if possible
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Feature.enabled?(:feature_flag)
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```
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To use feature gates based on actors, the model needs to respond to
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`flipper_id`. For example, to enable for the Foo model:
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```ruby
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class Foo < ActiveRecord::Base
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include FeatureGate
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end
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```
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Features that are developed and are intended to be merged behind a feature flag
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should not include a changelog entry. The entry should either be added in the merge
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request removing the feature flag or the merge request where the default value of
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the feature flag is set to true. If the feature contains any DB migration it
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should include a changelog entry for DB changes.
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In the rare case that you need the feature flag to be on automatically, use
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`default_enabled: true` when checking:
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```ruby
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Feature.enabled?(:feature_flag, project, default_enabled: true)
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```
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The [`Project#feature_available?`](https://gitlab.com/gitlab-org/gitlab/blob/4cc1c62918aa4c31750cb21dfb1a6c3492d71080/app/models/project_feature.rb#L63-68),
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[`Namespace#feature_available?`](https://gitlab.com/gitlab-org/gitlab/blob/4cc1c62918aa4c31750cb21dfb1a6c3492d71080/ee/app/models/ee/namespace.rb#L71-85) (EE), and
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[`License.feature_available?`](https://gitlab.com/gitlab-org/gitlab/blob/4cc1c62918aa4c31750cb21dfb1a6c3492d71080/ee/app/models/license.rb#L293-300) (EE) methods all implicitly check for
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a by default enabled feature flag with the same name as the provided argument.
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For example if a feature is license-gated, there's no need to add an additional
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explicit feature flag check since the flag will be checked as part of the
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`License.feature_available?` call. Similarly, there's no need to "clean up" a
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feature flag once the feature has reached general availability.
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You'd still want to use an explicit `Feature.enabled?` check if your new feature
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isn't gated by a License or Plan.
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**An important side-effect of the implicit feature flags mentioned above is that
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unless the feature is explicitly disabled or limited to a percentage of users,
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the feature flag check will default to `true`.**
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This is relevant when developing the feature using
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[several smaller merge requests](https://about.gitlab.com/handbook/values/#make-small-merge-requests), or when the feature is considered to be an
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[alpha or beta](https://about.gitlab.com/handbook/product/#alpha-beta-ga), and
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should not be available by default.
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As an example, if you were to ship the frontend half of a feature without the
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backend, you'd want to disable the feature entirely until the backend half is
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also ready to be shipped. To make sure this feature is disabled for both
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GitLab.com and self-managed instances, you should use the
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[`Namespace#alpha_feature_available?`](https://gitlab.com/gitlab-org/gitlab/blob/458749872f4a8f27abe8add930dbb958044cb926/ee/app/models/ee/namespace.rb#L113) or
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[`Namespace#beta_feature_available?`](https://gitlab.com/gitlab-org/gitlab/blob/458749872f4a8f27abe8add930dbb958044cb926/ee/app/models/ee/namespace.rb#L100-112)
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method, according to our [definitions](https://about.gitlab.com/handbook/product/#alpha-beta-ga). This ensures the feature is disabled unless the feature flag is
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_explicitly_ enabled.
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## Feature groups
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Starting from GitLab 9.4 we support feature groups via
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[Flipper groups](https://github.com/jnunemaker/flipper/blob/v0.10.2/docs/Gates.md#2-group).
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Feature groups must be defined statically in `lib/feature.rb` (in the
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`.register_feature_groups` method), but their implementation can obviously be
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dynamic (querying the DB etc.).
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Once defined in `lib/feature.rb`, you will be able to activate a
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feature for a given feature group via the [`feature_group` parameter of the features API](../../api/features.md#set-or-create-a-feature)
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### Frontend
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For frontend code you can use the method `push_frontend_feature_flag`, which is
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available to all controllers that inherit from `ApplicationController`. Using
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this method you can expose the state of a feature flag as follows:
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```ruby
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before_action do
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push_frontend_feature_flag(:vim_bindings)
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end
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def index
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# ...
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end
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def edit
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# ...
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end
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```
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You can then check for the state of the feature flag in JavaScript as follows:
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```javascript
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if ( gon.features.vimBindings ) {
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// ...
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}
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```
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The name of the feature flag in JavaScript will always be camelCased, meaning
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that checking for `gon.features.vim_bindings` would not work.
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See the [Vue guide](../fe_guide/vue.md#accessing-feature-flags) for details about
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how to access feature flags in a Vue component.
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### Specs
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In the test environment `Feature.enabled?` is stubbed to always respond to `true`,
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so we make sure behavior under feature flag doesn't go untested in some non-specific
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contexts.
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Whenever a feature flag is present, make sure to test _both_ states of the
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feature flag.
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See the
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[testing guide](../testing_guide/best_practices.md#feature-flags-in-tests)
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for information and examples on how to stub feature flags in tests.
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### Enabling a feature flag (in development)
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In the rails console (`rails c`), enter the following command to enable your feature flag
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```ruby
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Feature.enable(:feature_flag_name)
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```
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Similarly, the following command will disable a feature flag:
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```ruby
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Feature.disable(:feature_flag_name)
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```
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