[rails] Add feature flags to Rails integration

docs/GettingStarted.md

@@ -651,6 +651,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | ``distributed_tracing`` | Enables [distributed tracing](#distributed-tracing) so that this service trace is connected with a trace of another service if tracing headers are received | `false` |
 | ``middleware_names`` | Enables any short-circuited middleware requests to display the middleware name as resource for the trace. | `false` |
 | ``template_base_path`` | Used when the template name is parsed. If you don't store your templates in the ``views/`` folder, you may need to change this value | ``views/`` |
+| ``flags`` | Flags used in `rails` instrumentation. | ```{ instrument_action_view_rendering: true, instrument_action_controller_processing: true, instrument_active_support_caching: true, use_rack_integration: true, use_active_record_integration: true}``` |
 | ``tracer`` | A ``Datadog::Tracer`` instance used to instrument the application. Usually you don't need to set that. | ``Datadog.tracer`` |
 
 ### Redis

lib/ddtrace/contrib/rails/framework.rb

@@ -23,8 +23,9 @@ module Framework
         def self.setup
           config = config_with_defaults
 
-          activate_rack!(config)
-          activate_active_record!(config)
+          activate_rack!(config) if datadog_configuration[:flags][:use_rack_integration]
+          activate_active_record!(config) if datadog_configuration[:flags][:use_active_record_integration]
+
           set_service_info!(config)
 
           # By default, default service would be guessed from the script
@@ -69,6 +70,10 @@ def self.set_service_info!(config)
           tracer.set_service_info(config[:controller_service], 'rails', Ext::AppTypes::WEB)
           tracer.set_service_info(config[:cache_service], 'rails', Ext::AppTypes::CACHE)
         end
+
+        def self.datadog_configuration
+          Datadog.configuration[:rails]
+        end
       end
     end
   end

lib/ddtrace/contrib/rails/patcher.rb

@@ -6,6 +6,15 @@ module Rails
       # Patcher
       module Patcher
         include Base
+
+        DEFAULT_FLAGS = {
+          instrument_action_view_rendering: true,
+          instrument_action_controller_processing: true,
+          instrument_active_support_caching: true,
+          use_rack_integration: true,
+          use_active_record_integration: true
+        }.freeze
+
         register_as :rails, auto_patch: true
 
         option :service_name
@@ -21,6 +30,7 @@ module Patcher
         option :distributed_tracing, default: false
         option :template_base_path, default: 'views/'
         option :exception_controller, default: nil
+        option :flags, setter: ->(value) { DEFAULT_FLAGS.merge(value) }, default: DEFAULT_FLAGS
         option :tracer, default: Datadog.tracer
 
         @patched = false

lib/ddtrace/contrib/rails/railtie.rb

@@ -13,9 +13,20 @@ class Railtie < Rails::Railtie
 
     config.after_initialize do
       Datadog::Contrib::Rails::Framework.setup
-      Datadog::Contrib::Rails::ActionController.instrument
-      Datadog::Contrib::Rails::ActionView.instrument
-      Datadog::Contrib::Rails::ActiveSupport.instrument
+
+      if datadog_configuration[:flags][:instrument_action_controller_processing]
+        Datadog::Contrib::Rails::ActionController.instrument
+      end
+      if datadog_configuration[:flags][:instrument_action_view_rendering]
+        Datadog::Contrib::Rails::ActionView.instrument
+      end
+      if datadog_configuration[:flags][:instrument_active_support_caching]
+        Datadog::Contrib::Rails::ActiveSupport.instrument
+      end
+    end
+
+    def self.datadog_configuration
+      Datadog.configuration[:rails]
     end
   end
 end