OpenFeature Ruby SDK

OpenFeature is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool or in-house solution.

🚀 Quick start

Requirements

Supported Ruby Version	OS
Ruby 3.4.x	Windows, MacOS, Linux
Ruby 4.0.x	Windows, MacOS, Linux

This project supports all Ruby versions in active maintenance per the Ruby maintenance schedule.

Install

Install the gem and add to the application's Gemfile by executing:

bundle add openfeature-sdk

If bundler is not being used to manage dependencies, install the gem by executing:

gem install openfeature-sdk

Usage

require'open_feature/sdk'# API Initialization and configurationOpenFeature::SDK.configuredo |config|
# your provider of choice, which will be used as the default providerconfig.set_provider(OpenFeature::SDK::Provider::InMemoryProvider.new({"flag1"=>true,"flag2"=>1}))end# Create a clientclient=OpenFeature::SDK.build_client# fetching boolean value feature flagbool_value=client.fetch_boolean_value(flag_key: 'boolean_flag',default_value: false)# a details method is also available for more information about the flag evaluation# see `EvaluationDetails` for more infobool_details=client.fetch_boolean_details(flag_key: 'boolean_flag',default_value: false)# fetching string value feature flagstring_value=client.fetch_string_value(flag_key: 'string_flag',default_value: 'default')# fetching number value feature flagfloat_value=client.fetch_number_value(flag_key: 'number_value',default_value: 1.0)integer_value=client.fetch_number_value(flag_key: 'number_value',default_value: 1)# get an object valueobject=client.fetch_object_value(flag_key: 'object_value',default_value: {name: 'object'})

🌟 Features

Status	Features	Description
✅	Providers	Integrate with a commercial, open source, or in-house feature management tool.
✅	Targeting	Contextually-aware flag evaluation using evaluation context.
✅	Hooks	Add functionality to various stages of the flag evaluation life-cycle.
✅	Logging	Integrate with popular logging packages.
✅	Domains	Logically bind clients with providers.
✅	Eventing	React to state changes in the provider or flag management system.
✅	Shutdown	Gracefully clean up a provider during application shutdown.
✅	Tracking	Associate user actions with feature flag evaluations for experimentation.
✅	Transaction Context Propagation	Set a specific evaluation context for a transaction (e.g. an HTTP request or a thread)
✅	Extending	Extend OpenFeature with custom providers and hooks.

_{Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌}

Providers

Providers are an abstraction between a flag management system and the OpenFeature SDK. Look here for a complete list of available providers.

If the provider you're looking for hasn't been created yet, see the develop a provider section to learn how to build it yourself.

Once you've added a provider as a dependency, it can be registered with OpenFeature like this:

OpenFeature::SDK.configuredo |config|
# your provider of choice, which will be used as the default providerconfig.set_provider(OpenFeature::SDK::Provider::InMemoryProvider.new({"v2_enabled"=>true,}))end

Blocking Provider Registration

If you need to ensure that a provider is fully initialized before continuing, you can use set_provider_and_wait:

# Using the SDK directlybeginOpenFeature::SDK.set_provider_and_wait(my_provider)puts"Provider is ready!"rescueOpenFeature::SDK::ProviderInitializationError=>eputs"Provider failed to initialize: #{e.message}"puts"Error code: #{e.error_code}"# original_error contains the underlying exception that caused the initialization failureputs"Original error: #{e.original_error}"end# With custom timeout (default is 30 seconds)OpenFeature::SDK.set_provider_and_wait(my_provider,timeout: 60)# Domain-specific providerOpenFeature::SDK.set_provider_and_wait(my_provider,domain: "feature-flags")# Via configuration blockOpenFeature::SDK.configuredo |config|
beginconfig.set_provider_and_wait(my_provider)rescueOpenFeature::SDK::ProviderInitializationError=>e# Handle initialization failureendend

The set_provider_and_wait method:

• Waits for the provider's init method to complete successfully
• Raises ProviderInitializationError if initialization fails or times out
• Provides access to the provider instance, error code, and original exception for debugging
• The original_error field contains the underlying exception that caused the initialization failure
• Uses the same thread-safe provider switching as set_provider

In some situations, it may be beneficial to register multiple providers in the same application. This is possible using domains, which is covered in more detail below.

Targeting

Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as targeting. If the flag management system you're using supports targeting, you can provide the input data using the evaluation context.

OpenFeature::SDK.configuredo |config|
# you can set a global evaluation context hereconfig.evaluation_context=OpenFeature::SDK::EvaluationContext.new("host"=>"myhost.com")end# Evaluation context can be set on a client as wellclient_with_context=OpenFeature::SDK.build_client(evaluation_context: OpenFeature::SDK::EvaluationContext.new("controller_name"=>"admin"))# Invocation evaluation context can also be passed in during flag evaluation.# During flag evaluation, invocation context takes precedence over client context# which takes precedence over API (aka global) context.bool_value=client.fetch_boolean_value(flag_key: 'boolean_flag',default_value: false,evaluation_context: OpenFeature::SDK::EvaluationContext.new("is_friday"=>true))

Hooks

Hooks allow for custom logic to be added at well-defined points of the flag evaluation life-cycle. Look here for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the develop a hook section to learn how to build it yourself.

Hooks can be registered at the global, client, or flag invocation level.

# Define a hookclassMyHookincludeOpenFeature::SDK::Hooks::Hookdefbefore(hook_context:,hints:)puts"Evaluating flag: #{hook_context.flag_key}"nilenddefafter(hook_context:,evaluation_details:,hints:)puts"Flag #{hook_context.flag_key} evaluated to: #{evaluation_details.value}"enddeferror(hook_context:,exception:,hints:)puts"Error evaluating #{hook_context.flag_key}: #{exception.message}"enddeffinally(hook_context:,evaluation_details:,hints:)puts"Evaluation complete for #{hook_context.flag_key}"endend# Register at the API (global) levelOpenFeature::SDK.hooks << MyHook.new# Register at the client levelclient=OpenFeature::SDK.build_clientclient.hooks << MyHook.new# Register at the invocation levelclient.fetch_boolean_value(flag_key: "my-flag",default_value: false,hooks: [MyHook.new])

Logging

The SDK includes a built-in LoggingHook that provides structured log output for flag evaluations. It logs at the before, after, and error stages of the hook lifecycle.

# Use the SDK's default logger (from Configuration)OpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new# Or provide your own loggerlogger=Logger.new($stdout)OpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new(logger: logger)# Optionally include evaluation context in log outputOpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new(logger: logger,include_evaluation_context: true)

Log output uses a structured key=value format:

• before (DEBUG): stage=before domain=my-domain provider_name=my-provider flag_key=my-flag default_value=false
• after (DEBUG): includes reason, variant, and value
• error (ERROR): includes error_code and error_message

Domains

Clients can be assigned to a domain. A domain is a logical identifier which can be used to associate clients with a particular provider. If a domain has no associated provider, the default provider is used.

OpenFeature::SDK.configuredo |config|
config.set_provider(OpenFeature::SDK::Provider::NoOpProvider.new,domain: "legacy_flags")end# Create a client for a different domain, this will use the provider assigned to that domainlegacy_flag_client=OpenFeature::SDK.build_client(domain: "legacy_flags")

Eventing

Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (PROVIDER_READY on success, PROVIDER_ERROR on failure) are dispatched for every provider. Some providers support additional events, such as PROVIDER_CONFIGURATION_CHANGED.

Please refer to the documentation of the provider you're using to see what events are supported.

# Register event handlers at the API (global) levelready_handler=->(event_details)doputs"Provider #{event_details[:provider].metadata.name} is ready!"endOpenFeature::SDK.add_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_READY,ready_handler)# The SDK automatically emits lifecycle events. Providers can emit additional spontaneous events# using the EventEmitter mixin to signal internal state changes like configuration updates.classMyEventAwareProviderincludeOpenFeature::SDK::Provider::EventEmitterdefinit(evaluation_context)# Start background process to monitor for configuration changes# Note: SDK automatically emits PROVIDER_READY when init completes successfullystart_background_processenddefstart_background_processThread.newdo# Monitor for configuration changes and emit events when they occurifconfiguration_changed?emit_event(OpenFeature::SDK::ProviderEvent::PROVIDER_CONFIGURATION_CHANGED,message: "Flag configuration updated")endendendend# Remove specific handlers when no longer neededOpenFeature::SDK.remove_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_READY,ready_handler)

Shutdown

The OpenFeature API provides a shutdown method to perform cleanup of all registered providers. This should only be called when your application is in the process of shutting down.

# Shut down all registered providers and clear stateOpenFeature::SDK.shutdown

Individual providers can implement a shutdown method to perform cleanup:

classMyProviderdefshutdown# Perform any shutdown/reclamation steps with flag management system hereendend

Tracking

The tracking API allows you to use OpenFeature abstractions and objects to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. For example, a flag enhancing the appearance of a UI component might drive user engagement to a new feature; to test this hypothesis, telemetry collected by a hook or provider can be associated with telemetry reported in the client's track function.

client=OpenFeature::SDK.build_client# Simple tracking eventclient.track("checkout_completed")# With evaluation contextclient.track("purchase",evaluation_context: OpenFeature::SDK::EvaluationContext.new(targeting_key: "user-123"))# With tracking event details (optional numeric value + custom fields)details=OpenFeature::SDK::TrackingEventDetails.new(value: 99.99,plan: "premium",currency: "USD")client.track("subscription",tracking_event_details: details)

Note that some providers may not support tracking; if the provider does not implement a track method, the call is a no-op. Check the documentation for your provider for more information.

Transaction Context Propagation

Transaction context is a container for transaction-specific evaluation context (e.g. user id, user agent, IP). Transaction context can be set where specific data is available (e.g. an auth service or request handler) and by using the transaction context propagator it will automatically be applied to all flag evaluations within a transaction (e.g. a request or thread).

The SDK ships with a ThreadLocalTransactionContextPropagator that stores context in Thread.current:

# Set up the propagatorOpenFeature::SDK.set_transaction_context_propagator(OpenFeature::SDK::ThreadLocalTransactionContextPropagator.new)# Set transaction context (e.g. in a request middleware)OpenFeature::SDK.set_transaction_context(OpenFeature::SDK::EvaluationContext.new(targeting_key: "user-123","email"=>"user@example.com"))# Transaction context is automatically merged during flag evaluation.# Merge precedence: invocation > client > transaction > API (global)client=OpenFeature::SDK.build_clientclient.fetch_boolean_value(flag_key: "my-flag",default_value: false)

You can implement a custom propagator by including the TransactionContextPropagator module:

classMyRequestScopedPropagatorincludeOpenFeature::SDK::TransactionContextPropagatordefset_transaction_context(evaluation_context)# Store context in your request-scoped storageRequestStore[:openfeature_context]=evaluation_contextenddefget_transaction_contextRequestStore[:openfeature_context]endend

Extending

Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. You’ll then need to write the provider by implementing the Provider duck.

classMyProviderdefinit# Perform any initialization steps with flag management system here# Return value is ignored# **Note** The OpenFeature spec defines a lifecycle method called `initialize` to be called when a new provider is set.# To avoid conflicting with the Ruby `initialize` method, this method should be named `init` when creating a provider.enddefshutdown# Perform any shutdown/reclamation steps with flag management system here# Return value is ignoredenddeffetch_boolean_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a boolean value from provider sourceenddeffetch_string_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a string value from provider sourceenddeffetch_number_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a numeric value from provider sourceenddeffetch_integer_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a integer value from provider sourceenddeffetch_float_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a float value from provider sourceenddeffetch_object_value(flag_key:,default_value:,evaluation_context: nil)# Retrieve a hash value from provider sourceend# Optional: implement tracking support (spec 6.1.4)# If not defined, Client#track is a no-opdeftrack(tracking_event_name,evaluation_context:,tracking_event_details:)# Record a tracking event with your flag management systemendend

Built a new provider? Let us know so we can add it to the docs!

Develop a hook

To develop a hook, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. Implement your own hook by including the OpenFeature::SDK::Hooks::Hook module. You only need to define the stages you care about — unimplemented stages are no-ops by default.

classMyLoggingHookincludeOpenFeature::SDK::Hooks::Hookdefbefore(hook_context:,hints:)puts"Evaluating #{hook_context.flag_key}"nil# Return nil or an EvaluationContext to mergeenddefafter(hook_context:,evaluation_details:,hints:)puts"Result: #{evaluation_details.value}"end# error and finally are optional — only define what you needend

Built a new hook? Let us know so we can add it to the docs!

⭐️ Support the project

• Give this repo a ⭐️!
• Follow us on social media:
  • Twitter: @openfeature
  • LinkedIn: OpenFeature
• Join us on Slack
• For more, check out our community page

🤝 Contributing

Interested in contributing? Great, we'd love your help! To get started, take a look at the CONTRIBUTING guide.

Thanks to everyone who has already contributed

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