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---
stage: none
group: unassigned
info: "See the Technical Writers assigned to Development Guidelines: https://handbook.gitlab.com/handbook/product/ux/technical-writing/#assignments-to-development-guidelines"
---
# Feature flags in the development of GitLab
NOTE:
This document explains how to contribute to the development and operations of the GitLab product.
If you want to use feature flags to show and hide functionality in your own applications,
view [this feature flags information](../../operations/feature_flags.md) instead.
WARNING:
All newly-introduced feature flags should be [disabled by default](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#feature-flags-in-gitlab-development).
WARNING:
All newly-introduced feature flags should be [used with an actor](controls.md#percentage-based-actor-selection).
Blueprints:
- (Latest) [Feature Flags usage in GitLab development and operations](../../architecture/blueprints/feature_flags_usage_in_dev_and_ops/index.md)
- [Development Feature Flags Architecture](../../architecture/blueprints/feature_flags_development/index.md)
This document is the subject of continued work as part of an epic to [improve internal usage of feature flags](https://gitlab.com/groups/gitlab-org/-/epics/3551). Raise any suggestions as new issues and attach them to the epic.
For an [overview of the feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#feature-flag-lifecycle), or if you need help deciding [if you should use a feature flag](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags) or not, see the [feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/) handbook page.
## When to use feature flags
Moved to the ["When to use feature flags"](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags) section in the handbook.
## Feature flags in GitLab development
The following highlights should be considered when deciding if feature flags
should be leveraged:
- The feature flag must be **disabled by default**.
- Feature flags should remain in the codebase for as short period as possible
to reduce the need for feature flag accounting.
- The person operating the feature flag is responsible for clearly communicating
the status of a feature behind the feature flag in the documentation and with other stakeholders. The
issue description should be updated with the feature flag name and whether it is
defaulted on or off as soon it is evident that a feature flag is needed.
- Merge requests that introduce a feature flag, update its state, or remove the
existing feature flag because a feature is deemed stable must have the
~"feature flag" label assigned.
When the feature implementation is delivered over multiple merge requests:
1. [Create a new feature flag](#create-a-new-feature-flag)
which is **disabled** by default, in the first merge request which uses the flag.
Flags [should not be added separately](#risk-of-a-broken-default-branch).
1. Submit incremental changes via one or more merge requests, ensuring that any
new code added can only be reached if the feature flag is **enabled**.
You can keep the feature flag enabled on your local GDK during development.
1. When the feature is ready to be tested by other team members, [create the initial documentation](../documentation/feature_flags.md#when-to-document-features-behind-a-feature-flag).
Include details about the status of the [feature flag](../documentation/feature_flags.md#how-to-add-feature-flag-documentation).
1. Enable the feature flag for a specific group/project/user and ensure that there are no issues
with the implementation. Do not enable the feature flag for a public project
like `gitlab-org/gitlab` if there is no documentation. Team members and contributors might search for
documentation on how to use the feature if they see it enabled in a public project.
1. When the feature is ready for production use, open a merge request to:
- Update the documentation to describe the latest flag status.
- Add a [changelog entry](#changelog).
- Remove the feature flag to enable the new behavior, or flip the feature flag to be **enabled by default** (only for `ops` and `beta` feature flags).
One might be tempted to think that feature flags will delay the release of a
feature by at least one month (= one release). This is not the case. A feature
flag does not have to stick around for a specific amount of time
(for example, at least one release), instead they should stick around until the feature
is deemed stable. **Stable means it works on GitLab.com without causing any
problems, such as outages.**
## Risk of a broken default branch
Feature flags must be used in the MR that introduces them. Not doing so causes a
[broken default branch](https://about.gitlab.com/handbook/engineering/workflow/#broken-master) scenario due
to the `rspec:feature-flags` job that only runs on the default branch.
## Types of feature flags
Choose a feature flag type that matches the expected usage.
### `gitlab_com_derisk` type
`gitlab_com_derisk` feature flags are short-lived feature flags,
used to de-risk GitLab.com deployments. Most feature flags used at
GitLab are of the `gitlab_com_derisk` type.
#### Constraints
- `default_enabled`: **Must not** be set to true. This kind of feature flag is meant to lower the risk on GitLab.com, thus there's no need to keep the flag in the codebase after it's been enabled on GitLab.com. `default_enabled: true` will not have any effect for this type of feature flag.
- Maximum Lifespan: 2 months after it's merged into the default branch
- Documentation: This type of feature flag don't need to be documented in the
[All feature flags in GitLab](../../user/feature_flags.md) page given they're short-lived and deployment-related
- Rollout issue: **Must** have a rollout issue created from the
[Feature flag Roll Out template](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20Flag%20Roll%20Out.md)
#### Usage
The format for `gitlab_com_derisk` feature flags is `Feature.<state>(:<dev_flag_name>)`.
To enable and disable them, run on the GitLab Rails console:
```ruby
# To enable it for the instance:
Feature.enable(:<dev_flag_name>, type: :gitlab_com_derisk)
# To disable it for the instance:
Feature.disable(:<dev_flag_name>, type: :gitlab_com_derisk)
# To enable for a specific project:
Feature.enable(:<dev_flag_name>, Project.find(<project id>), type: :gitlab_com_derisk)
# To disable for a specific project:
Feature.disable(:<dev_flag_name>, Project.find(<project id>), type: :gitlab_com_derisk)
```
To check a `gitlab_com_derisk` feature flag's state:
```ruby
# Check if the feature flag is enabled
Feature.enabled?(:dev_flag_name, type: :gitlab_com_derisk)
# Check if the feature flag is disabled
Feature.disabled?(:dev_flag_name, type: :gitlab_com_derisk)
```
### `wip` type
Some features are complex and need to be implemented through several MRs. Until they're fully implemented,
it needs to be hidden from anyone. In that case, the `wip` (for "Work In Progress") feature flag allows
to merge all the changes to the main branch without actually using the feature yet.
Once the feature is complete, the feature flag type can be changed to the `gitlab_com_derisk` or
`beta` type depending on how the feature will be presented/documented to customers.
#### Constraints
- `default_enabled`: **Must not** be set to true. If needed, this type can be changed to beta once the feature is complete.
- Maximum Lifespan: 4 months after it's merged into the default branch
- Documentation: This type of feature flag don't need to be documented in the
[All feature flags in GitLab](../../user/feature_flags.md) page given they're mostly hiding unfinished code
- Rollout issue: Likely no need for a rollout issues, as `wip` feature flags should be transitioned to
another type before being enabled
#### Usage
```ruby
# Check if feature flag is enabled
Feature.enabled?(:my_wip_flag, project, type: :wip)
# Check if feature flag is disabled
Feature.disabled?(:my_wip_flag, project, type: :wip)
# Push feature flag to Frontend
push_frontend_feature_flag(:my_wip_flag, project, type: :wip)
```
### `beta` type
We might
[not be confident we'll be able to scale, support, and maintain a feature](https://about.gitlab.com/handbook/product/gitlab-the-product/#experiment-beta-ga)
in its current form for every designed use case ([example](https://gitlab.com/gitlab-org/gitlab/-/issues/336070#note_1523983444)).
There are also scenarios where a feature is not complete enough to be considered an MVC.
Providing a flag in this case allows engineers and customers to disable the new feature until it's performant enough.
#### Constraints
- `default_enabled`: Can be set to `true` so that a feature can be "released" to everyone in Beta with the
possibility to disable it in the case of scalability issues (ideally it should only be disabled for this
reason on specific on-premise installations)
- Maximum Lifespan: 6 months after it's merged into the default branch
- Documentation: This type of feature flag **must** be documented in the
[All feature flags in GitLab](../../user/feature_flags.md) page
- Rollout issue: **Must** have a rollout issue
created from the
[Feature flag Roll Out template](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20Flag%20Roll%20Out.md)
#### Usage
```ruby
# Check if feature flag is enabled
Feature.enabled?(:my_beta_flag, project, type: :beta)
# Check if feature flag is disabled
Feature.disabled?(:my_beta_flag, project, type: :beta)
# Push feature flag to Frontend
push_frontend_feature_flag(:my_beta_flag, project, type: :beta)
```
### `ops` type
`ops` feature flags are long-lived feature flags that control operational aspects
of GitLab product behavior. For example, feature flags that disable features that might
have a performance impact such as Sidekiq worker behavior.
Remember that using this type should follow a conscious decision not to introduce an
instance/group/project/user setting.
#### Constraints
- `default_enabled`: Can be set to `true` so that a feature can be "released" to everyone in Beta with the
possibility to disable it in the case of scalability issues (ideally it should only be disabled for this
reason on specific on-premise installations)
- Maximum Lifespan: Unlimited
- Documentation: This type of feature flag **must** be documented in the
[All feature flags in GitLab](../../user/feature_flags.md) page
- Rollout issue: Likely no need for a rollout issues, as it is hard to predict when they are enabled or disabled
#### Usage
```ruby
# Check if feature flag is enabled
Feature.enabled?(:my_ops_flag, project, type: :ops)
# Check if feature flag is disabled
Feature.disabled?(:my_ops_flag, project, type: :ops)
# Push feature flag to Frontend
push_frontend_feature_flag(:my_ops_flag, project, type: :ops)
```
### `experiment` type
`experiment` feature flags are used for A/B testing on GitLab.com.
An `experiment` feature flag should conform to the same standards as a `beta` feature flag,
although the interface has some differences. An experiment feature flag should have a rollout issue,
created using the [Experiment Tracking template](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Experiment%20Rollout.md). More information can be found in the [experiment guide](../experiment_guide/index.md).
#### Constraints
- `default_enabled`: **Must not** be set to `true`.
- Maximum Lifespan: 6 months after it's merged into the default branch
### `worker` type
`worker` feature flags are special `ops` flags that allow to control Sidekiq workers behavior, such as deferring Sidekiq jobs.
`worker` feature flags likely do not have any YAML definition as the name could be dynamically generated using
the worker name itself, for example, `run_sidekiq_jobs_AuthorizedProjectsWorker`. Some examples for using `worker` type feature
flags can be found in [deferring Sidekiq jobs](#deferring-sidekiq-jobs).
### [Deprecated]`development` type
The `development` type is deprecated in favor of the `gitlab_com_derisk`, `wip`, and `beta` feature flag types.
## Feature flag definition and validation
> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/229161) in GitLab 13.3.
During development (`RAILS_ENV=development`) or testing (`RAILS_ENV=test`) all feature flag usage is being strictly validated.
This process is meant to ensure consistent feature flag usage in the codebase. All feature flags **must**:
- Be known. Only use feature flags that are explicitly defined.
- Not be defined twice. They have to be defined either in FOSS or EE, but not both.
- Use a valid and consistent `type:` across all invocations.
- Have an owner.
All feature flags known to GitLab are self-documented in YAML files stored in:
- [`config/feature_flags`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/config/feature_flags)
- [`ee/config/feature_flags`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/ee/config/feature_flags)
Each feature flag is defined in a separate YAML file consisting of a number of fields:
| Field | Required | Description |
|---------------------|----------|----------------------------------------------------------------|
| `name` | yes | Name of the feature flag. |
| `type` | yes | Type of feature flag. |
| `default_enabled` | yes | The default state of the feature flag. |
| `introduced_by_url` | yes | The URL to the merge request that introduced the feature flag. |
| `milestone` | yes | Milestone in which the feature flag was created. |
| `group` | yes | The [group](https://about.gitlab.com/handbook/product/categories/#devops-stages) that owns the feature flag. |
| `feature_issue_url` | no | The URL to the original feature issue. |
| `rollout_issue_url` | no | The URL to the Issue covering the feature flag rollout. |
NOTE:
All validations are skipped when running in `RAILS_ENV=production`.
## Create a new feature flag
NOTE:
GitLab Pages uses [a different process](../pages/index.md#feature-flags) for feature flags.
The GitLab codebase provides [`bin/feature-flag`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/bin/feature-flag),
a dedicated tool to create new feature flag definitions.
The tool asks various questions about the new feature flag, then creates
a YAML definition in `config/feature_flags` or `ee/config/feature_flags`.
Only feature flags that have a YAML definition file can be used when running the development or testing environments.
```shell
$ bin/feature-flag my_feature_flag
>> Specify the group introducing the feature flag, like `group::project management`:
?> group::cloud connector
>> URL of the MR introducing the feature flag (enter to skip):
?> https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38602
>> Open this URL and fill in the rest of the details:
https://gitlab.com/gitlab-org/gitlab/-/issues/new?issue%5Btitle%5D=%5BFeature+flag%5D+Rollout+of+%60test-flag%60&issuable_template=Feature+Flag+Roll+Out
>> URL of the rollout issue (enter to skip):
?> https://gitlab.com/gitlab-org/gitlab/-/issues/232533
create config/feature_flags/development/my_feature_flag.yml
---
name: my_feature_flag
introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38602
rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/232533
group: group::cloud connector
type: development
default_enabled: false
```
All newly-introduced feature flags must be [**disabled by default**](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#feature-flags-in-gitlab-development).
Features that are developed and merged behind a feature flag
should not include a changelog entry. The entry should be added either in the merge
request removing the feature flag or the merge request where the default value of
the feature flag is set to enabled. If the feature contains any database migrations, it
*should* include a changelog entry for the database changes.
NOTE:
To create a feature flag that is only used in EE, add the `--ee` flag: `bin/feature-flag --ee`
### Naming new flags
When choosing a name for a new feature flag, consider the following guidelines:
- A long, descriptive name is better than a short but confusing one.
- Write the name in snake case (`my_cool_feature_flag`).
- Avoid using `disable` in the name to avoid having to think (or [document](../documentation/feature_flags.md))
with double negatives. Consider starting the name with `hide_`, `remove_`, or `disallow_`.
In software engineering this problem is known as
["negative names for boolean variables"](https://www.serendipidata.com/posts/naming-guidelines-for-boolean-variables).
But we can't forbid negative words altogether, to be able to introduce flags as
[disabled by default](#feature-flags-in-gitlab-development), use them to remove a feature by moving it behind a flag, or to [selectively disable a flag by actor](controls.md#selectively-disable-by-actor).
### Risk of a broken master (main) branch
WARNING:
Feature flags **must** be used in the MR that introduces them. Not doing so causes a
[broken master](https://about.gitlab.com/handbook/engineering/workflow/#broken-master) scenario due
to the `rspec:feature-flags` job that only runs on the `master` branch.
## List all the feature flags
To [use ChatOps](../../ci/chatops/index.md) to output all the feature flags in an environment to Slack, you can use the `run feature list`
command. For example:
```shell
/chatops run feature list --dev
/chatops run feature list --staging
```
## Toggle a feature flag
See [rolling out changes](controls.md#rolling-out-changes) for more information about toggling
feature flags.
## Delete a feature flag
See [cleaning up feature flags](controls.md#cleaning-up) for more information about
deleting feature flags.
## Develop with a feature flag
There are two main ways of using feature flags in the GitLab codebase:
- [Backend code (Rails)](#backend)
- [Frontend code (VueJS)](#frontend)
### Backend
The feature flag interface is defined in [`lib/feature.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/feature.rb).
This interface provides a set of methods to check if the feature flag is enabled or disabled:
```ruby
if Feature.enabled?(:my_feature_flag, project)
# execute code if feature flag is enabled
else
# execute code if feature flag is disabled
end
if Feature.disabled?(:my_feature_flag, project)
# execute code if feature flag is disabled
end
```
Default behavior for not configured feature flags is controlled
by `default_enabled:` in YAML definition.
If feature flag does not have a YAML definition an error will be raised
in development or test environment, while returning `false` on production.
If not specified, the default feature flag type for `Feature.enabled?` and `Feature.disabled?`
is `type: development`. For all other feature flag types, you must specify the `type:`:
```ruby
if Feature.enabled?(:feature_flag, project, type: :ops)
# execute code if ops feature flag is enabled
else
# execute code if ops feature flag is disabled
end
if Feature.disabled?(:my_feature_flag, project, type: :ops)
# execute code if feature flag is disabled
end
```
WARNING:
Don't use feature flags at application load time. For example, using the `Feature` class in
`config/initializers/*` or at the class level could cause an unexpected error. This error occurs
because a database that a feature flag adapter might depend on doesn't exist at load time
(especially for fresh installations). Checking for the database's existence at the caller isn't
recommended, as some adapters don't require a database at all (for example, the HTTP adapter). The
feature flag setup check must be abstracted in the `Feature` namespace. This approach also requires
application reload when the feature flag changes. You must therefore ask SREs to reload the
Web/API/Sidekiq fleet on production, which takes time to fully rollout/rollback the changes. For
these reasons, use environment variables (for example, `ENV['YOUR_FEATURE_NAME']`) or `gitlab.yml`
instead.
Here's an example of a pattern that you should avoid:
```ruby
class MyClass
if Feature.enabled?(:...)
new_process
else
legacy_process
end
end
```
#### Recursion detection
When there are many feature flags, it is not always obvious where they are
called. Avoid cycles where the evaluation of one feature flag requires the
evaluation of other feature flags. If this causes a cycle, it will be broken
and the default value will be returned.
To enable this recursion detection to work correctly, always access feature values through
`Feature::enabled?`, and avoid the low-level use of `Feature::get`. When this
happens, we track a `Feature::RecursionError` exception to the error tracker.
### Frontend
When using a feature flag for UI elements, make sure to _also_ use a feature
flag for the underlying backend code, if there is any. This ensures there is
absolutely no way to use the feature until it is enabled.
Use the `push_frontend_feature_flag` method which is available to all controllers that inherit from `ApplicationController`. You can use this method to expose the state of a feature flag, for example:
```ruby
before_action do
# Prefer to scope it per project or user, for example
push_frontend_feature_flag(:vim_bindings, project)
end
def index
# ...
end
def edit
# ...
end
```
You can then check the state of the feature flag in JavaScript as follows:
```javascript
if ( gon.features.vimBindings ) {
// ...
}
```
The name of the feature flag in JavaScript is always camelCase,
so checking for `gon.features.vim_bindings` would not work.
See the [Vue guide](../fe_guide/vue.md#accessing-feature-flags) for details about
how to access feature flags in a Vue component.
If not specified, the default feature flag type for `push_frontend_feature_flag`
is `type: development`. For all other feature flag types, you must specify the `type:`:
```ruby
before_action do
push_frontend_feature_flag(:vim_bindings, project, type: :ops)
end
```
### Feature actors
**It is strongly advised to use actors with feature flags.** Actors provide a simple
way to enable a feature flag only for a given project, group or user. This makes debugging
easier, as you can filter logs and errors for example, based on actors. This also makes it possible
to enable the feature on the `gitlab-org` or `gitlab-com` groups first, while the rest of
the users aren't impacted.
Actors also provide an easy way to do a percentage rollout of a feature in a sticky way.
If a 1% rollout enabled a feature for a specific actor, that actor will continue to have the feature enabled at
10%, 50%, and 100%.
GitLab currently supports the following feature flag actors:
- `User` model
- `Project` model
- `Group` model
- Current request
The actor is a second parameter of the `Feature.enabled?` call. The
same actor type must be used consistently for all invocations of `Feature.enabled?`.
```ruby
# Bad
Feature.enabled?(:feature_flag, project)
Feature.enabled?(:feature_flag, group)
Feature.enabled?(:feature_flag, user)
# Good
Feature.enabled?(:feature_flag, group_a)
Feature.enabled?(:feature_flag, group_b)
# Also good - using separate flags for each actor type
Feature.enabled?(:feature_flag_group, group)
Feature.enabled?(:feature_flag_user, user)
```
See [Feature flags in the development of GitLab](controls.md#process) for details on how to use ChatOps
to selectively enable or disable feature flags in GitLab-provided environments, like staging and production.
#### Current request actor
> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/132078) in GitLab 16.5
It is not recommended to use percentage of time rollout, as each call may return
inconsistent results.
Rather it is advised to use the current request as an actor.
```ruby
# Bad
Feature.enable_percentage_of_time(:feature_flag, 40)
Feature.enabled?(:feature_flag)
# Good
Feature.enable_percentage_of_actors(:feature_flag, 40)
Feature.enabled?(:feature_flag, Feature.current_request)
```
When using the current request as the actor, the feature flag should return the
same value within the context of a request.
As the current request actor is implemented using [`SafeRequestStore`](../caching.md#low-level), we should
have consistent feature flag values within:
- a Rack request
- a Sidekiq worker execution
- an ActionCable worker execution
To migrate an existing feature from percentage of time to the current request
actor, it is recommended that you create a new feature flag.
This is because it is difficult to control the timing between existing
`percentage_of_time` values, the deployment of the code change, and switching to
use `percentage_of_actors`.
#### Use actors for verifying in production
WARNING:
Using production as a testing environment is not recommended. Use our testing
environments for testing features that are not production-ready.
While the staging environment provides a way to test features in an environment
that resembles production, it doesn't allow you to compare before-and-after
performance metrics specific to production environment. It can be useful to have a
project in production with your development feature flag enabled, to allow tools
like Sitespeed reports to reveal the metrics of the new code under a feature flag.
This approach is even more useful if you're already tracking the old codebase in
Sitespeed, enabling you to compare performance accurately before and after the
feature flag's rollout.
### Enable additional objects as actors
To use feature gates based on actors, the model needs to respond to
`flipper_id`. For example, to enable for the Foo model:
```ruby
class Foo < ActiveRecord::Base
include FeatureGate
end
```
Only models that `include FeatureGate` or expose `flipper_id` method can be
used as an actor for `Feature.enabled?`.
### Feature flags for licensed features
You can't use a feature flag with the same name as a licensed feature name, because
it would cause a naming collision. This was [widely discussed and removed](https://gitlab.com/gitlab-org/gitlab/-/issues/259611)
because it is confusing.
To check for licensed features, add a dedicated feature flag under a different name
and check it explicitly, for example:
```ruby
Feature.enabled?(:licensed_feature_feature_flag, project) &&
project.feature_available?(:licensed_feature)
```
### Feature groups
Feature groups must be defined statically in `lib/feature.rb` (in the
`.register_feature_groups` method), but their implementation can be
dynamic (querying the DB, for example).
Once defined in `lib/feature.rb`, you can to activate a
feature for a given feature group via the [`feature_group` parameter of the features API](../../api/features.md#set-or-create-a-feature)
The available feature groups are:
| Group name | Scoped to | Description |
| --------------------- | --------- | ----------- |
| `gitlab_team_members` | Users | Enables the feature for users who are members of [`gitlab-com`](https://gitlab.com/gitlab-com) |
Feature groups can be enabled via the group name:
```ruby
Feature.enable(:feature_flag_name, :gitlab_team_members)
```
### Enabling a feature flag locally (in development)
In the rails console (`rails c`), enter the following command to enable a feature flag:
```ruby
Feature.enable(:feature_flag_name)
```
Similarly, the following command disables a feature flag:
```ruby
Feature.disable(:feature_flag_name)
```
You can also enable a feature flag for a given gate:
```ruby
Feature.enable(:feature_flag_name, Project.find_by_full_path("root/my-project"))
```
### Disabling a feature flag locally (in development)
When manually enabling or disabling a feature flag from the Rails console, its default value gets overwritten.
This can cause confusion when changing the flag's `default_enabled` attribute.
To reset the feature flag to the default status, you can disable it in the rails console (`rails c`)
as follows:
```ruby
Feature.remove(:feature_flag_name)
```
## Changelog
We want to avoid introducing a changelog when features are not accessible by an end-user either directly (example: ability to use the feature) or indirectly (examples: ability to take advantage of background jobs, performance improvements, or database migration updates).
- Database migrations are always accessible by an end-user indirectly, as self-managed customers need to be aware of database changes before upgrading. For this reason, they **should** have a changelog entry.
- Any change behind a feature flag **disabled** by default **should not** have a changelog entry.
- Any change behind a feature flag that is **enabled** by default **should** have a changelog entry.
- Changing the feature flag itself (flag removal, default-on setting) **should** have [a changelog entry](../changelog.md).
Use the flowchart to determine the changelog entry type.
```mermaid
graph LR
A[flag: default off] -->|'added' / 'changed' / 'fixed' / '...'| B(flag: default on)
B -->|'other'| C(remove flag, keep new code)
B -->|'removed' / 'changed'| D(remove flag, keep old code)
A -->|'added' / 'changed' / 'fixed' / '...'| C
A -->|no changelog| D
```
- The changelog for a feature flag should describe the feature and not the
flag, unless a default on feature flag is removed keeping the new code (`other` in the flowchart above).
- A feature flag can also be used for rolling out a bug fix or a maintenance work. In this scenario, the changelog
must be related to it, for example; `fixed` or `other`.
## Feature flags in tests
Introducing a feature flag into the codebase creates an additional code path that should be tested.
It is strongly advised to include automated tests for all code affected by a feature flag, both when **enabled** and **disabled**
to ensure the feature works properly. If automated tests are not included for both states, the functionality associated
with the untested code path should be manually tested before deployment to production.
When using the testing environment, all feature flags are enabled by default.
Flags can be disabled by default in the [`spec/spec_helper.rb` file](https://gitlab.com/gitlab-org/gitlab/-/blob/b61fba42eea2cf5bb1ca64e80c067a07ed5d1921/spec/spec_helper.rb#L274).
Add a comment inline to explain why the flag needs to be disabled. You can also attach the issue URL for reference if possible.
WARNING:
This does not apply to end-to-end (QA) tests, which [do not enable feature flags by default](#end-to-end-qa-tests). There is a different [process for using feature flags in end-to-end tests](../testing_guide/end_to_end/feature_flags.md).
To disable a feature flag in a test, use the `stub_feature_flags`
helper. For example, to globally disable the `ci_live_trace` feature
flag in a test:
```ruby
stub_feature_flags(ci_live_trace: false)
Feature.enabled?(:ci_live_trace) # => false
```
A common pattern of testing both paths looks like:
```ruby
it 'ci_live_trace works' do
# tests assuming ci_live_trace is enabled in tests by default
Feature.enabled?(:ci_live_trace) # => true
end
context 'when ci_live_trace is disabled' do
before do
stub_feature_flags(ci_live_trace: false)
end
it 'ci_live_trace does not work' do
Feature.enabled?(:ci_live_trace) # => false
end
end
```
If you wish to set up a test where a feature flag is enabled only
for some actors and not others, you can specify this in options
passed to the helper. For example, to enable the `ci_live_trace`
feature flag for a specific project:
```ruby
project1, project2 = build_list(:project, 2)
# Feature will only be enabled for project1
stub_feature_flags(ci_live_trace: project1)
Feature.enabled?(:ci_live_trace) # => false
Feature.enabled?(:ci_live_trace, project1) # => true
Feature.enabled?(:ci_live_trace, project2) # => false
```
The behavior of FlipperGate is as follows:
1. You can enable an override for a specified actor to be enabled.
1. You can disable (remove) an override for a specified actor,
falling back to the default state.
1. There's no way to model that you explicitly disabled a specified actor.
```ruby
Feature.enable(:my_feature)
Feature.disable(:my_feature, project1)
Feature.enabled?(:my_feature) # => true
Feature.enabled?(:my_feature, project1) # => true
Feature.disable(:my_feature2)
Feature.enable(:my_feature2, project1)
Feature.enabled?(:my_feature2) # => false
Feature.enabled?(:my_feature2, project1) # => true
```
### `have_pushed_frontend_feature_flags`
Use `have_pushed_frontend_feature_flags` to test if [`push_frontend_feature_flag`](#frontend)
has added the feature flag to the HTML.
For example,
```ruby
stub_feature_flags(value_stream_analytics_path_navigation: false)
visit group_analytics_cycle_analytics_path(group)
expect(page).to have_pushed_frontend_feature_flags(valueStreamAnalyticsPathNavigation: false)
```
### `stub_feature_flags` vs `Feature.enable*`
It is preferred to use `stub_feature_flags` to enable feature flags
in the testing environment. This method provides a simple and well described
interface for simple use cases.
However, in some cases more complex behavior needs to be tested,
like percentage rollouts of feature flags. This can be done using
`.enable_percentage_of_time` or `.enable_percentage_of_actors`:
```ruby
# Good: feature needs to be explicitly disabled, as it is enabled by default if not defined
stub_feature_flags(my_feature: false)
stub_feature_flags(my_feature: true)
stub_feature_flags(my_feature: project)
stub_feature_flags(my_feature: [project, project2])
# Bad
Feature.enable(:my_feature_2)
# Good: enable my_feature for 50% of time
Feature.enable_percentage_of_time(:my_feature_3, 50)
# Good: enable my_feature for 50% of actors/gates/things
Feature.enable_percentage_of_actors(:my_feature_4, 50)
```
Each feature flag that has a defined state is persisted
during test execution time:
```ruby
Feature.persisted_names.include?('my_feature') => true
Feature.persisted_names.include?('my_feature_2') => true
Feature.persisted_names.include?('my_feature_3') => true
Feature.persisted_names.include?('my_feature_4') => true
```
### Stubbing actor
When you want to enable a feature flag for a specific actor only,
you can stub its representation. A gate that is passed
as an argument to `Feature.enabled?` and `Feature.disabled?` must be an object
that includes `FeatureGate`.
In specs you can use the `stub_feature_flag_gate` method that allows you to
quickly create a custom actor:
```ruby
gate = stub_feature_flag_gate('CustomActor')
stub_feature_flags(ci_live_trace: gate)
Feature.enabled?(:ci_live_trace) # => false
Feature.enabled?(:ci_live_trace, gate) # => true
```
You can also disable a feature flag for a specific actor:
```ruby
gate = stub_feature_flag_gate('CustomActor')
stub_feature_flags(ci_live_trace: false, thing: gate)
```
### Controlling feature flags engine in tests
Our Flipper engine in the test environment works in a memory mode `Flipper::Adapters::Memory`.
`production` and `development` modes use `Flipper::Adapters::ActiveRecord`.
You can control whether the `Flipper::Adapters::Memory` or `ActiveRecord` mode is being used.
#### `stub_feature_flags: true` (default and preferred)
In this mode Flipper is configured to use `Flipper::Adapters::Memory` and mark all feature
flags to be on-by-default and persisted on a first use.
Make sure behavior under feature flag doesn't go untested in some non-specific contexts.
### `stub_feature_flags: false`
This disables a memory-stubbed flipper, and uses `Flipper::Adapters::ActiveRecord`
a mode that is used by `production` and `development`.
You should use this mode only when you really want to tests aspects of Flipper
with how it interacts with `ActiveRecord`.
### End-to-end (QA) tests
Toggling feature flags works differently in end-to-end (QA) tests. The end-to-end test framework does not have direct access to
Rails or the database, so it can't use Flipper. Instead, it uses [the public API](../../api/features.md#set-or-create-a-feature). Each end-to-end test can [enable or disable a feature flag during the test](../testing_guide/end_to_end/feature_flags.md). Alternatively, you can enable or disable a feature flag before one or more tests when you [run them from your GitLab repository's `qa` directory](https://gitlab.com/gitlab-org/gitlab/-/tree/master/qa#running-tests-with-a-feature-flag-enabled-or-disabled), or if you [run the tests via GitLab QA](https://gitlab.com/gitlab-org/gitlab-qa/-/blob/master/docs/what_tests_can_be_run.md#running-tests-with-a-feature-flag-enabled).
[As noted above, feature flags are not enabled by default in end-to-end tests.](#feature-flags-in-tests)
This means that end-to-end tests will run with feature flags in the default state implemented in the source
code, or with the feature flag in its current state on the GitLab instance under test, unless the
test is written to enable/disable a feature flag explicitly.
When a feature flag is changed on Staging or on GitLab.com, a Slack message will be posted to the `#qa-staging` or `#qa-production` channels to inform
the pipeline triage DRI so that they can more easily determine if any failures are related to a feature flag change. However, if you are working on a change you can
help to avoid unexpected failures by [confirming that the end-to-end tests pass with a feature flag enabled.](../testing_guide/end_to_end/feature_flags.md#confirming-that-end-to-end-tests-pass-with-a-feature-flag-enabled)
## Controlling Sidekiq worker behavior with feature flags
Feature flags with [`worker` type](#worker-type) can be used to control the behavior of a Sidekiq worker.
### Deferring Sidekiq jobs
When disabled, feature flags with the format of `run_sidekiq_jobs_{WorkerName}` delay the execution of the worker
by scheduling the job at a later time. This feature flag is enabled by default for all workers.
Deferring jobs can be useful during an incident where contentious behavior from
worker instances are saturating infrastructure resources (such as database and database connection pool).
The implementation can be found at [SkipJobs Sidekiq server middleware](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/sidekiq_middleware/skip_jobs.rb).
NOTE:
Jobs are deferred indefinitely as long as the feature flag is disabled. It is important to remove the
feature flag after the worker is deemed safe to continue processing.
When set to false, 100% of the jobs are deferred. When you want processing to resume, you can
use a **percentage of time** rollout. For example:
```shell
# not running any jobs, deferring all 100% of the jobs
/chatops run feature set run_sidekiq_jobs_SlowRunningWorker false
# only running 10% of the jobs, deferring 90% of the jobs
/chatops run feature set run_sidekiq_jobs_SlowRunningWorker 10
# running 50% of the jobs, deferring 50% of the jobs
/chatops run feature set run_sidekiq_jobs_SlowRunningWorker 50
# back to running all jobs normally
/chatops run feature delete run_sidekiq_jobs_SlowRunningWorker
```
### Dropping Sidekiq jobs
Instead of [deferring jobs](#deferring-sidekiq-jobs), jobs can be entirely dropped by enabling the feature flag
`drop_sidekiq_jobs_{WorkerName}`. Use this feature flag when you are certain the jobs are safe to be dropped, i.e.
the jobs do not need to be processed in the future.
```shell
# drop all the jobs
/chatops run feature set drop_sidekiq_jobs_SlowRunningWorker true
# process jobs normally
/chatops run feature delete drop_sidekiq_jobs_SlowRunningWorker
```
NOTE:
Dropping feature flag (`drop_sidekiq_jobs_{WorkerName}`) takes precedence over deferring feature flag (`run_sidekiq_jobs_{WorkerName}`),
i.e. when `drop_sidekiq_jobs` is enabled and `run_sidekiq_jobs` is disabled, jobs are entirely dropped.
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