Ruby SDK reference

Overview

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

Get started

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

Install the SDK

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:

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require 'ldclient-rb'

Initialize the client

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:

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client = LaunchDarkly::LDClient.new("sdk-key-123abc")

The Ruby SDK relies on multiple background threads to operate correctly. When a process forks, the SDK will not function correctly in the child process until it is reinitialized. Use the postfork() method to reinitialize an existing client after a process fork.

Here’s how:

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client = LaunchDarkly::LDClient.new("sdk-key-123abc")
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# From the child process, reinitialize the client by calling `postfork`.
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client.postfork()

Any configuration that you provide to the SDK must survive the forking process independently. We recommend that you add any listeners or hooks after the postfork() call, unless you are certain they can survive the forking process.

If you are using the Relay Proxy, you must use Relay Proxy v8.11 or later to use postfork().

To learn more about the specific configuration options available in this SDK, read Config. To learn more about the postfork() reinitialization, read postfork.

Initialize the client while using a Rails application

If you are using a Rails application, do not use the above method to initialize the client. Instead, follow the instructions below for your application.

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Rails.configuration.client = LaunchDarkly::LDClient.new("sdk-key-123abc")

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Spring.after_fork do
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  Rails.configuration.client.postfork()
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end

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after_fork do |server,worker|
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  Rails.configuration.client.postfork()
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end

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on_worker_boot do
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  Rails.configuration.client.postfork()
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end

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if defined?(PhusionPassenger)
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  PhusionPassenger.on_event(:starting_worker_process) do |forked|
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    Rails.configuration.client.postfork()
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  end
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end

Initialize the client while using httplog

If you are using the Rails httplog library, you should include launchdarkly.com in the url_blacklist_pattern attribute of httplog’s configuration.

By default, the Rails httplog library buffers the entire response to a request. However, in the LaunchDarkly SDKs, the streaming request remains open. Therefore, the httplog library intercepts the request but never returns the response from LaunchDarkly indicating that initialization is complete. This means the Ruby SDK may not complete initialization and also may not log an error. If your application makes flag evaluations before the SDK initialization is complete, you may receive the message: [LDClient] Client has not finished initializing; feature store unavailable, returning default value.

When you include launchdarkly.com in the url_blacklist_pattern attribute of httplog’s configuration, then httplog will not intercept the response, and SDK initialization will complete. This lets you use flags as expected.

To learn more, read the httplog Configuration documentation.

Evaluate a context

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 Context configuration.

Here’s how:

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context = LaunchDarkly::LDContext.with_key("user-key-123abc")
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show_feature = client.variation("flag-key-123abc", context, false)
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if show_feature
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  # application code to show the feature
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else
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  # the code to run if the feature is off
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end

Shut down the client

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:

• Anonymous contexts and users
• Big segments
• Configuration, including
  • Application metadata configuration
  • Migration configuration
  • Service endpoint configuration
• Context configuration
• Evaluating flags
• Flag evaluation reasons
• Flushing events
• Getting all flags
• Hooks
• Identifying and changing contexts
• Logging configuration
• Migrations
• Monitoring SDK status
• Offline mode
• OpenTelemetry
• Private attributes
• Reading flags from a file
• Relay Proxy configuration
  • Using proxy mode
  • Using daemon mode
• Secure mode
• Sending custom events
• Shutting down
• Storing data
• Subscribing to flag changes
• Test data sources
• Web proxy configuration