feat: ruby observability plugin (#360)

Author: ccschmitz-launchdarkly

.gitignore

@@ -38,6 +38,7 @@ docker/enterprise-private.pem
 # Editor Artifacts
 **/.idea
 .vscode/*.log
+.cursor/rules/
 
 dump.rdb
 

e2e/ruby/rails/api-only/Gemfile

@@ -46,4 +46,6 @@ group :development do
   # gem "spring"
 end
 
-gem 'highlight_io', path: '../../../../sdk/highlight-ruby/highlight'
+# LaunchDarkly SDK and Observability Plugin
+gem 'launchdarkly-server-sdk', '~> 8.0'
+gem 'launchdarkly-observability', path: '../../../../sdk/@launchdarkly/observability-ruby'

e2e/ruby/rails/api-only/Gemfile.lock

@@ -1,3 +1,9 @@
 class ApplicationController < ActionController::API
   include ActionController::Cookies
+
+  private
+
+  def ld_client
+    Rails.configuration.ld_client
+  end
 end

e2e/ruby/rails/api-only/app/controllers/application_controller.rb

@@ -1,9 +1,64 @@
 class HealthController < ApplicationController
   def index
-    render(json: { status: 'ok', timestamp: Time.current })
+    context = LaunchDarkly::LDContext.create({ key: 'health-check', kind: 'service' })
+    state = ld_client.all_flags_state(context)
+
+    render(json: {
+      status: 'ok',
+      timestamp: Time.current,
+      launchdarkly: {
+        connected: state.valid?,
+        flag_count: state.values_map.size
+      }
+    })
   end
 
   def error
     raise(StandardError, 'Test API error')
   end
+
+  # GET /health/flags
+  # Returns all flag evaluations for testing
+  def flags
+    user_key = params[:user_key] || 'anonymous'
+    context = LaunchDarkly::LDContext.create({ key: user_key, kind: 'user' })
+
+    state = ld_client.all_flags_state(context)
+
+    # Get detailed evaluations for all flags
+    evaluations = {}
+    state.values_map.each_key do |flag_key|
+      detail = ld_client.variation_detail(flag_key, context, nil)
+      evaluations[flag_key] = {
+        value: detail.value,
+        variation_index: detail.variation_index,
+        reason: detail.reason&.kind
+      }
+    end
+
+    render(json: {
+      valid: state.valid?,
+      context_key: user_key,
+      flag_count: evaluations.size,
+      evaluations: evaluations
+    })
+  end
+
+  # GET /health/flags/:key
+  # Evaluate a specific flag
+  def flag
+    flag_key = params[:key]
+    user_key = params[:user_key] || 'anonymous'
+    context = LaunchDarkly::LDContext.create({ key: user_key, kind: 'user' })
+
+    detail = ld_client.variation_detail(flag_key, context, nil)
+
+    render(json: {
+      flag_key: flag_key,
+      context_key: user_key,
+      value: detail.value,
+      variation_index: detail.variation_index,
+      reason: detail.reason ? JSON.parse(detail.reason.to_json) : nil
+    })
+  end
 end

e2e/ruby/rails/api-only/app/controllers/health_controller.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require 'launchdarkly-server-sdk'
+require 'launchdarkly_observability'
+
+# Create observability plugin (SDK key and environment automatically inferred)
+observability_plugin = LaunchDarklyObservability::Plugin.new(
+  otlp_endpoint: ENV.fetch('OTEL_EXPORTER_OTLP_ENDPOINT', 'http://localhost:4318'),
+  service_name: 'launchdarkly-ruby-api-only',
+  service_version: '1.0.0'
+)
+
+# Initialize LaunchDarkly client with real SDK key
+sdk_key = ENV.fetch('LAUNCHDARKLY_SDK_KEY') do
+  Rails.logger.warn '[LaunchDarkly] LAUNCHDARKLY_SDK_KEY not set, client will not connect'
+  nil
+end
+
+config = LaunchDarkly::Config.new(
+  plugins: [observability_plugin]
+)
+
+Rails.configuration.ld_client = LaunchDarkly::LDClient.new(sdk_key, config)
+
+at_exit { Rails.configuration.ld_client.close }
+
+Rails.logger.info '[LaunchDarkly] Client initialized with observability plugin'

e2e/ruby/rails/api-only/config/initializers/highlight.rb

@@ -4,5 +4,7 @@
   root to: 'health#index'
 
   get 'health', to: 'health#index'
+  get 'health/flags', to: 'health#flags'
+  get 'health/flags/:key', to: 'health#flag'
   get 'error', to: 'health#error'
 end

e2e/ruby/rails/api-only/config/initializers/launchdarkly.rb

@@ -17,8 +17,8 @@ class HealthControllerTest < ActionDispatch::IntegrationTest
     end
   end
 
-  test 'should include highlight headers' do
-    get health_path, headers: { 'X-Highlight-Request' => 'test-session/test-request' }
+  test 'should handle custom headers' do
+    get health_path, headers: { 'X-Request-ID' => 'test-request-123' }
     assert_response :success
   end
 end

e2e/ruby/rails/api-only/config/routes.rb

@@ -72,6 +72,6 @@ group :test do
   gem 'selenium-webdriver'
 end
 
-gem 'highlight_io', path: '../../../../sdk/highlight-ruby/highlight'
-
-gem 'rubocop', '~> 1.65'
+# LaunchDarkly SDK and Observability Plugin
+gem 'launchdarkly-server-sdk', '~> 8.0'
+gem 'launchdarkly-observability', path: '../../../../sdk/@launchdarkly/observability-ruby'