261 lines
10 KiB
Markdown
261 lines
10 KiB
Markdown
---
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stage: Release
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group: Progressive Delivery
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
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---
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# Feature Flags **(PREMIUM)**
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/7433) in GitLab 11.4.
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With Feature Flags, you can deploy your application's new features to production in smaller batches.
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You can toggle a feature on and off to subsets of users, helping you achieve Continuous Delivery.
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Feature flags help reduce risk, allowing you to do controlled testing, and separate feature
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delivery from customer launch.
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<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
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For an example of feature flags in action, see [GitLab for Deploys, Feature Flags, and Error Tracking](https://www.youtube.com/embed/5tw2p6lwXxo).
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## How it works
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GitLab uses [Unleash](https://github.com/Unleash/unleash), a feature
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toggle service.
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By enabling or disabling a flag in GitLab, your application
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can determine which features to enable or disable.
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You can create feature flags in GitLab and use the API from your application
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to get the list of feature flags and their statuses. The application must be configured to communicate
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with GitLab, so it's up to developers to use a compatible client library and
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[integrate the feature flags in your app](#integrate-feature-flags-with-your-application).
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## Create a feature flag
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To create and enable a feature flag:
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1. Navigate to your project's **Operations > Feature Flags**.
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1. Click the **New feature flag** button.
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1. Enter a name that starts with a letter and contains only lowercase letters, digits, underscores (`_`)
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and dashes (`-`), and does not end with a dash (`-`) or underscore (`_`).
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1. Enter a description (optional, 255 characters max).
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1. Enter details about how the flag should be applied:
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- In GitLab 13.0 and earlier: Enter an environment spec,
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enable or disable the flag in this environment, and select a rollout strategy.
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- In GitLab 13.1 and later (when [this feature flag](#feature-flag-behavior-change-in-130) is enabled): Select a strategy and then
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the environments to apply the strategy to.
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1. Click **Create feature flag**.
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The feature flag is displayed in the list. It is enabled by default.
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## Disable a feature flag for a specific environment
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In [GitLab 13.0 and earlier](https://gitlab.com/gitlab-org/gitlab/-/issues/8621),
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to disable a feature flag for a specific environment:
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1. Navigate to your project's **Operations > Feature Flags**.
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1. For the feature flag you want to disable, click the Pencil icon.
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1. To disable the flag:
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- In GitLab 13.0 and earlier: Slide the Status toggle for the environment. Or, to delete the
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environment spec, on the right, click the **Remove (X)** icon.
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- In GitLab 13.1 and later (when [this feature flag](#feature-flag-behavior-change-in-130) is
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enabled): For each strategy it applies to, under **Environments**, delete the environment.
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1. Click **Save changes**.
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## Disable a feature flag for all environments
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To disable a feature flag for all environments:
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1. Navigate to your project's **Operations > Feature Flags**.
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1. For the feature flag you want to disable, slide the Status toggle to **Disabled**.
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The feature flag is displayed on the **Disabled** tab.
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## Feature flag behavior change in 13.0
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/35555) in GitLab 13.0.
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Starting in GitLab 13.0, you can apply a feature flag strategy across multiple environments,
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without defining the strategy multiple times.
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This feature is under development and not ready for production use. It is
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deployed behind a feature flag that is **disabled by default**.
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[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
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can enable it for your instance.
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To enable it:
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```ruby
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Feature.enable(:feature_flags_new_version)
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```
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To disable it:
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```ruby
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Feature.disable(:feature_flags_new_version)
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```
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## Feature flag strategies
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GitLab Feature Flag uses [Unleash](https://unleash.github.io)
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as the feature flag engine. In Unleash, there is a concept of rulesets for granular feature flag controls,
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called [strategies](https://unleash.github.io/docs/activation_strategy).
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Supported strategies for GitLab Feature Flags are described below.
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### Rollout strategy
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/8240) in GitLab 12.2.
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The selected rollout strategy affects which users will experience the feature as enabled.
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The status of an environment spec ultimately determines whether or not a feature is enabled at all.
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For instance, a feature will always be disabled for every user if the matching environment spec has a disabled status, regardless of the chosen rollout strategy.
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However, a feature will be enabled for 50% of logged-in users if the matching environment spec has an enabled status along with a **Percent rollout (logged in users)** strategy set to 50%.
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#### All users
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Enables the feature for all users. It is implemented using the Unleash
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[`default`](https://unleash.github.io/docs/activation_strategy#default)
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activation strategy.
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#### Percent rollout (logged in users)
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Enables the feature for a percentage of authenticated users. It is
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implemented using the Unleash
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[`gradualRolloutUserId`](https://unleash.github.io/docs/activation_strategy#gradualrolloutuserid)
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activation strategy.
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Set a value of 15%, for example, to enable the feature for 15% of authenticated users.
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A rollout percentage may be between 0% and 100%.
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CAUTION: **Caution:**
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If this strategy is selected, then the Unleash client **must** be given a user
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ID for the feature to be enabled. See the [Ruby example](#ruby-application-example) below.
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#### User IDs
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> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/8240) in GitLab 12.2. [Updated](https://gitlab.com/gitlab-org/gitlab/-/issues/34363) to be defined per environment in GitLab 12.6.
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A feature flag may be enabled for a list of target users. It is implemented
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using the Unleash [`userWithId`](https://unleash.github.io/docs/activation_strategy#userwithid)
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activation strategy.
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User IDs should be a comma-separated list of values. For example, `user@example.com, user2@example.com`, or `username1,username2,username3`, etc.
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CAUTION: **Caution:**
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The Unleash client **must** be given a user ID for the feature to be enabled for
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target users. See the [Ruby example](#ruby-application-example) below.
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## Integrate feature flags with your application
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To use feature flags with your application, get access credentials from GitLab.
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Then prepare your application with a client library.
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### Get access credentials
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To get the access credentials that your application needs to communicate with GitLab:
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1. Navigate to your project's **Operations > Feature Flags**.
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1. Click the **Configure** button to view the following:
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- **API URL**: URL where the client (application) connects to get a list of feature flags.
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- **Instance ID**: Unique token that authorizes the retrieval of the feature flags.
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- **Application name**: The name of the running environment. For instance,
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if the application runs for a production server, the application name would be
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`production` or similar. This value is used for the environment spec evaluation.
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NOTE: **Note:**
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The meaning of these fields might change over time. For example, we are not sure
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if **Instance ID** will be single token or multiple tokens, assigned to the
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**Environment**. Also, **Application name** could describe the version of
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application instead of the running environment.
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### Choose a client library
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GitLab implements a single backend that is compatible with Unleash clients.
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With the Unleash client, developers can define, in the application code, the default values for flags.
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Each feature flag evaluation can express the desired outcome if the flag isn't present in the
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provided configuration file.
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Unleash currently [offers many SDKs for various languages and frameworks](https://github.com/Unleash/unleash#client-implementations).
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### Feature flags API information
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For API content, see:
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- [Feature Flags API](../../../api/feature_flags.md)
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- [Feature Flag Specs API](../../../api/feature_flag_specs.md) (Deprecated and [scheduled for removal in GitLab 14.0](https://gitlab.com/gitlab-org/gitlab/-/issues/213369).)
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- [Feature Flag User Lists API](../../../api/feature_flag_user_lists.md)
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- [Legacy Feature Flags API](../../../api/feature_flags_legacy.md)
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### Golang application example
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Here's an example of how to integrate feature flags in a Golang application:
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```golang
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package main
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import (
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"io"
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"log"
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"net/http"
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"github.com/Unleash/unleash-client-go"
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)
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type metricsInterface struct {
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}
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func init() {
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unleash.Initialize(
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unleash.WithUrl("https://gitlab.com/api/v4/feature_flags/unleash/42"),
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unleash.WithInstanceId("29QmjsW6KngPR5JNPMWx"),
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unleash.WithAppName("production"),
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unleash.WithListener(&metricsInterface{}),
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)
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}
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func helloServer(w http.ResponseWriter, req *http.Request) {
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if unleash.IsEnabled("my_feature_name") {
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io.WriteString(w, "Feature enabled\n")
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} else {
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io.WriteString(w, "hello, world!\n")
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}
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}
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func main() {
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http.HandleFunc("/", helloServer)
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log.Fatal(http.ListenAndServe(":8080", nil))
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}
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```
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### Ruby application example
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Here's an example of how to integrate feature flags in a Ruby application.
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The Unleash client is given a user ID for use with a **Percent rollout (logged in users)** rollout strategy or a list of **Target Users**.
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```ruby
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#!/usr/bin/env ruby
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require 'unleash'
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require 'unleash/context'
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unleash = Unleash::Client.new({
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url: 'http://gitlab.com/api/v4/feature_flags/unleash/42',
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app_name: 'production',
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instance_id: '29QmjsW6KngPR5JNPMWx'
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})
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unleash_context = Unleash::Context.new
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# Replace "123" with the id of an authenticated user.
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# Note that the context's user id must be a string:
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# https://unleash.github.io/docs/unleash_context
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unleash_context.user_id = "123"
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if unleash.is_enabled?("my_feature_name", unleash_context)
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puts "Feature enabled"
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else
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puts "hello, world!"
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end
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```
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