Ruby Feature Flags

Docs > Feature Flags > Server-Side Feature Flags > Ruby Feature Flags

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Overview

This page describes how to instrument your Ruby application with the Datadog Feature Flags SDK.

Prerequisites

Before setting up the Ruby Feature Flags SDK, ensure you have:

Datadog Agent with Remote Configuration enabled
Datadog Ruby tracer datadog version 2.23.0 or later
OpenFeature Ruby SDK openfeature-sdk version 0.4.1 or later
Service and environment configured - Feature flags are targeted by service and environment

Installing and initializing

Feature Flagging is provided by Application Performance Monitoring (APM). To integrate APM into your application with feature flagging support, install the required gems and configure Remote Configuration with OpenFeature support.

gem install ddtrace openfeature-sdk

require 'datadog'
require 'open_feature/sdk'
require 'datadog/open_feature/provider'

# Configure Datadog with feature flagging enabled
Datadog.configure do |config|
  config.remote.enabled = true
  config.open_feature.enabled = true
end

# Configure OpenFeature SDK with Datadog provider
OpenFeature::SDK.configure do |config|
  config.set_provider(Datadog::OpenFeature::Provider.new)
end

# Create OpenFeature client
client = OpenFeature::SDK.build_client

The client returns default values until Remote Configuration loads in the background. This approach keeps your application responsive during startup but may serve defaults for early requests.

Set the evaluation context

Define an evaluation context that identifies the user or entity for flag targeting. The evaluation context includes attributes used to determine which flag variations should be returned:

context = OpenFeature::SDK::EvaluationContext.new(
  targetingKey: 'user-123',  # Targeting key (typically user ID)
  email: 'user@example.com',
  country: 'US',
  tier: 'premium',
  age: 25
)

The targeting key is used for consistent traffic distribution (percentage rollouts). Additional attributes enable targeting rules, such as “enable for users in the US” or “enable for premium tier users” in the example above.

Evaluate flags

After creating the OpenFeature client, you can start reading flag values throughout your app. Flag evaluation uses locally cached data, so no network requests occur when evaluating flags.

Each flag is identified by a unique string key. Flags are evaluated using typed methods that return values matching the expected type. The SDK returns the default value if a flag doesn’t exist or cannot be evaluated.

Boolean flags

Use fetch_boolean_value() for flags that represent on/off or true/false conditions:

enabled = client.fetch_boolean_value(
  flag_key: 'new-checkout-flow',
  default_value: false,
  evaluation_context: context
)

if enabled
  show_new_checkout
else
  show_legacy_checkout
end

String flags

Use fetch_string_value() for flags that select between multiple variants or configuration strings:

theme = client.fetch_string_value(
  flag_key: 'ui-theme',
  default_value: 'light',
  evaluation_context: context
)

case theme
when 'dark'
  set_dark_theme
when 'light'
  set_light_theme
else
  set_light_theme
end

Number flags

For numeric flags, use fetch_integer_value() or fetch_float_value(). Ruby also provides fetch_number_value(), which returns the appropriate type based on the default value. These methods are appropriate when a feature depends on a numeric parameter such as a limit, percentage, or multiplier:

max_items = client.fetch_integer_value(
  flag_key: 'cart-max-items',
  default_value: 20,
  evaluation_context: context
)

discount_rate = client.fetch_float_value(
  flag_key: 'discount-rate',
  default_value: 0.0,
  evaluation_context: context
)

# Generic number method (type based on default)
batch_size = client.fetch_number_value(
  flag_key: 'batch-size',
  default_value: 100,  # Returns integer
  evaluation_context: context
)

Object flags

For structured data, use fetch_object_value(). This method returns a hash. Object flags are useful for Remote Configuration scenarios where multiple properties need to be provided together.

config = client.fetch_object_value(
  flag_key: 'feature-config',
  default_value: {
    'maxRetries' => 3,
    'timeout' => 30
  },
  evaluation_context: context
)

max_retries = config['maxRetries'] || 3
timeout = config['timeout'] || 30

Flag evaluation details

When you need more than the flag value, use the fetch_<type>_details methods. These methods return both the evaluated value and metadata explaining the evaluation:

details = client.fetch_boolean_details(
  flag_key: 'new-feature',
  default_value: false,
  evaluation_context: context
)

puts "Value: #{details.value}"
puts "Variant: #{details.variant}"
puts "Reason: #{details.reason}"
puts "Error Code: #{details.error_code}"
puts "Error Message: #{details.error_message}"

Flag details help you debug evaluation behavior and understand why a user received a given value.

Evaluation without context

You can evaluate flags without providing an evaluation context. This is useful for global flags that don’t require user-specific targeting:

# Global feature flag - no context needed
maintenance_mode = client.fetch_boolean_value(
  flag_key: 'maintenance-mode',
  default_value: false
)

if maintenance_mode
  halt 503, { error: 'Service temporarily unavailable' }.to_json
end

Troubleshooting

Feature flags always return default values

If feature flags unexpectedly always return default values, check the following:

Verify Remote Configuration is enabled in your Datadog Agent configuration
Ensure the service and environment are configured (either through DD_SERVICE and DD_ENV environment variables or config.service and config.env in Ruby)
Check that config.remote.enabled = true and config.open_feature.enabled = true are set in your Ruby application’s Datadog configuration
Verify the datadog gem version includes OpenFeature support (2.23.0 or later)

Remote Configuration connection issues

Check the Datadog tracer logs for Remote Configuration status:

# Enable startup and debug logging
Datadog.configure do |config|
  config.diagnostics.startup_logs.enabled = true
  config.diagnostics.debug = true
  config.remote.enabled = true
  config.open_feature.enabled = true
end