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    Ruby SDK reference

    Read time: 2 minutes
    Last edited: May 04, 2023
    Version 7 of the Ruby SDK replaces users with contexts

    A context is a generalized way of referring to the people, services, machines, or other resources that encounter feature flags in your product. Contexts replace another data object in LaunchDarkly: "users."

    Code samples on this page are from the two most recent SDK versions where they differ. To learn more about upgrading, read Ruby SDK 6.x to 7.0 migration guide.


    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 applicationsRuby
    Rails with bootstrapping
    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.

    SDK version compatibility

    The LaunchDarkly Ruby SDK, version 7.0 and higher, is compatible with Ruby 2.7 and higher.

    Prior to version 7.0, the LaunchDarkly Ruby SDK also supported Ruby 2.5 and 2.6.

    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("sdk-key-123abc")
    LDClient must be a singleton

    It's important to make LDClient a singleton for each LaunchDarkly project. 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.

    If you have multiple LaunchDarkly projects, you can create one LDClient for each. In this situation, the clients operate independently. For example, they do not share a single connection to LaunchDarkly.

    You can use client to check which variation a particular context will receive for a given feature flag. To learn more, read Evaluating flags and Flag evaluation reasons. For more information about how contexts are specified, read User and context configuration.

    Here's how:

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

    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("sdk-key-123abc")

    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-123abc')

    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-123abc')

    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-123abc')

    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-123abc')

    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: