127 lines
3.9 KiB
Markdown
127 lines
3.9 KiB
Markdown
# Manage feature flags
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Starting from GitLab 9.3 we support feature flags for features in GitLab via
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[Flipper](https://github.com/jnunemaker/flipper/). You should use the `Feature`
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class (defined in `lib/feature.rb`) in your code to get, set and list feature
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flags.
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During runtime you can set the values for the gates via the
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[features API](../api/features.md) (accessible to admins only).
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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` param of the features API](../api/features.md#set-or-create-a-feature)
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For GitLab.com, team members have access to feature flags through chatops. Only
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percentage gates are supported at this time. Setting a feature to be used 50% of
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the time, you should execute `/chatops run feature set my_feature_flag 50`.
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## Feature flags for user applications
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This document only covers feature flags used in the development of GitLab
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itself. Feature flags in deployed user applications can be found at
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[Feature Flags](https://docs.gitlab.com/ee/user/project/operations/feature_flags.html)
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## 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` group first, while the rest of the users
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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 be added in the merge
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request removing the feature flags.
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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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For more information about rolling out changes using feature flags, refer to the
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[Rolling out changes using feature flags](rolling_out_changes_using_feature_flags.md)
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guide.
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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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### 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. You can stub a feature flag as follows:
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```ruby
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stub_feature_flags(my_feature_flag: false)
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```
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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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## Enabling a feature flag (in production)
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Check how to [roll out changes using feature flags](rolling_out_changes_using_feature_flags.md).
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