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    Ruby SDK reference

    Read time: 2 minutes
    Last edited: Sep 27, 2022

    This topic documents how to get started with the server-side Ruby SDK, and links to reference information on all of the supported features.

    SDK quick links

    LaunchDarkly's SDKs are open source. In addition to this reference guide, we provide source, API reference documentation, and sample applications:

    SDK API documentationSDK API docs
    GitHub repositoryruby-server-sdk
    Sample applicationshello-ruby (Ruby)
    hello-bootstrap-rails (Rails server-side bootstrapping example)
    Published moduleRubyGems
    RubyGems bug

    Due to a bug in recent versions of RubyGems, RubyGems versions 2.4.x are not compatible with the LaunchDarkly Ruby SDK.

    Getting started

    After you complete the Getting Started process, follow these instructions to start using the LaunchDarkly SDK in your Ruby application.

    First, install the LaunchDarkly SDK as a dependency in your application using your application's dependency manager. Refer to the SDK releases page to identify the latest version if you want to depend on a specific version.

    If you are using Bundler, you can add gem "launchdarkly-server-sdk" to your Gemfile and run bundle install. Otherwise, you can install the gem directly:

    gem install launchdarkly-server-sdk

    Next, import the LaunchDarkly client in your application code. This step may not be necessary if you are using a framework that automatically loads all dependencies, as Rails does.

    Here's how:

    require 'ldclient-rb'

    After you install and import the SDK, create a single, shared instance of LDClient. Specify your SDK key here to authorize your application to connect to a particular environment within LaunchDarkly.

    Here's how:

    client = LaunchDarkly::LDClient.new("YOUR_SDK_KEY")
    LDClient must be a singleton

    It's important to make LDClient a singleton. The client instance maintains internal state that allows LaunchDarkly to serve feature flags without making any remote requests. Do not instantiate a new client with every request.

    You can use client to check which variation a particular user will receive for a given feature flag.

    Here's how:

    show_feature = client.variation("your.flag.key", {key: "user@test.com"}, false)
    if show_feature
    # application code to show the feature
    # the code to run if the feature is off

    Lastly, when your application is about to terminate, shut down client. To learn more, read Shutting down.

    Initializing LDClient in a Rails Application

    To use LaunchDarkly in a Rails application, initialize the client in config/initializers/launchdarkly.rb:

    Rails.configuration.client = LaunchDarkly::LDClient.new("your_sdk_key")

    To use LaunchDarkly with the Rails application preloader Spring, we recommend using an after_fork callback in the config/spring.rb file:

    Spring.after_fork do
    Rails.configuration.client = LaunchDarkly::LDClient.new('SDK KEY')

    Similarly, with Unicorn, you'll need to specify an after_fork hook in your unicorn.rb config file:

    after_fork do |server,worker|
    Rails.configuration.client = LaunchDarkly::LDClient.new('SDK KEY')

    If you use the Puma web server, we recommend initializing the client in on_worker_boot, as well as initializing in the Rails app:

    on_worker_boot do
    Rails.configuration.client = LaunchDarkly::LDClient.new('SDK KEY')

    If you use the Passenger web server, we recommend initializing the client in config.ru, or from any code called while loading config.ru:

    if defined?(PhusionPassenger)
    PhusionPassenger.on_event(:starting_worker_process) do |forked|
    Rails.configuration.client = LaunchDarkly::LDClient.new('SDK KEY')

    Lastly, shut down the client when your application terminates. This frees the resources the worker threads were using and provides an explicit signal for the Ruby SDK to send the remaining event data back to LaunchDarkly. To learn more, read Shutting down.

    Supported features

    This SDK supports the following features: