[rails] Redis instrumentation follows users settings

lib/ddtrace.rb

@@ -31,24 +31,9 @@ def self.tracer
     require 'ddtrace/contrib/rails/framework'
 
     module Datadog
-      # Run the auto instrumentation directly after the initialization of the application and
-      # after the application initializers in config/initializers are run
+      # Run the auto instrumentation directly after initializers in
+      # `config/initializers` are executed
       class Railtie < Rails::Railtie
-        config.before_configuration do
-          begin
-            # We include 'redis-rails' here if it's available, doing it later
-            # (typically in initialize callback) does not work, it does not
-            # get loaded in the right context.
-            require 'redis-rails'
-            Datadog::Tracer.log.debug("'redis-rails' module found, Datadog 'redis-rails' integration is available")
-          rescue LoadError
-            Datadog::Tracer.log.debug("'redis-rails' module not found, Datadog 'redis-rails' integration is disabled")
-          end
-
-          Datadog::Monkey.patch_module(:redis)
-        end
-
-        # we do actions
         config.after_initialize do |app|
           Datadog::Contrib::Rails::Framework.configure(config: app.config)
           Datadog::Contrib::Rails::Framework.auto_instrument()

lib/ddtrace/contrib/rails/framework.rb

@@ -80,21 +80,32 @@ def self.configure(config)
         end
 
         def self.auto_instrument_redis
-          # configure Redis PIN
-          return unless (defined? ::Rails.cache) && ::Rails.cache.respond_to?(:data)
-          pin = Datadog::Pin.get_from(::Rails.cache.data)
-          return unless pin
+          return unless ::Rails.configuration.datadog_trace[:auto_instrument_redis]
+          Datadog::Tracer.log.debug('Enabling auto-instrumentation for Redis client')
 
-          # enable Redis instrumentation if activated
-          pin.tracer = nil unless ::Rails.configuration.datadog_trace[:auto_instrument_redis]
-          return unless pin.tracer
-          Datadog::Tracer.log.debug("'redis' module found, Datadog 'redis' integration is available")
+          # patch the Redis library and reload the CacheStore if it was using Redis
+          Datadog::Monkey.patch_module(:redis)
+
+          # reload the cache store if it's available and it's using Redis
+          return unless defined?(::ActiveSupport::Cache::RedisStore) &&
+                        defined?(::Rails.cache) &&
+                        ::Rails.cache.is_a?(::ActiveSupport::Cache::RedisStore)
+          Datadog::Tracer.log.debug('Enabling auto-instrumentation for redis-rails connector')
+
+          # backward compatibility: Rails 3.x doesn't have `cache=` method
+          cache_store = ::Rails.configuration.cache_store
+          cache_instance = ::ActiveSupport::Cache.lookup_store(cache_store)
+          if ::Rails::VERSION::MAJOR.to_i == 3
+            silence_warnings { Object.const_set 'RAILS_CACHE', cache_instance }
+          elsif ::Rails::VERSION::MAJOR.to_i > 3
+            ::Rails.cache = cache_instance
+          end
         end
 
         # automatically instrument all Rails component
         def self.auto_instrument
           return unless ::Rails.configuration.datadog_trace[:auto_instrument]
-          Datadog::Tracer.log.info('Detected Rails >= 3.x. Enabling auto-instrumentation for core components')
+          Datadog::Tracer.log.debug('Enabling auto-instrumentation for core components')
 
           # instrumenting Rails framework
           Datadog::Contrib::Rails::ActionController.instrument()

test/contrib/rails/apps/application.rb

@@ -1,6 +1,5 @@
 require 'rails/all'
 require 'rails/test_help'
-require 'contrib/rails/apps/cache'
 
 require 'ddtrace'
 
@@ -9,7 +8,9 @@ class TestApplication < Rails::Application
     # common settings between all Rails versions
     def initialize(*args)
       super(*args)
-      config.cache_store = get_cache
+      redis_cache = [:redis_store, { url: ENV['REDIS_URL'] }]
+      file_cache = [:file_store, '/tmp/ddtrace-rb/cache/']
+      config.cache_store = ENV['REDIS_URL'] ? redis_cache : file_cache
       config.eager_load = false
       config.secret_key_base = 'not_so_secret'
     end

test/contrib/rails/apps/rails3.rb

@@ -1,11 +1,12 @@
 require 'rails/all'
 require 'rails/test_help'
-require 'contrib/rails/apps/cache'
 
 require 'ddtrace'
 
 class Rails3 < Rails::Application
-  config.cache_store = get_cache
+  redis_cache = [:redis_store, { url: ENV['REDIS_URL'] }]
+  file_cache = [:file_store, '/tmp/ddtrace-rb/cache/']
+  config.cache_store = ENV['REDIS_URL'] ? redis_cache : file_cache
   config.secret_key_base = 'not_so_secret'
   config.active_support.test_order = :random
   config.active_support.deprecation = :stderr

test/contrib/rails/redis_cache_test.rb

@@ -11,11 +11,14 @@
 
 class RedisCacheTracingTest < ActionController::TestCase
   setup do
+    # switch Rails with a dummy tracer
     @original_tracer = Rails.configuration.datadog_trace[:tracer]
     @tracer = get_test_tracer()
     Rails.configuration.datadog_trace[:tracer] = @tracer
-    assert_equal(true, Rails.cache.respond_to?(:data), "cache '#{Rails.cache}' has no data")
-    pin = Datadog::Pin.get_from(Rails.cache.data)
+
+    # get the Redis pin accessing private methods (only Rails 3.x)
+    client = Rails.cache.instance_variable_get(:@data)
+    pin = Datadog::Pin.get_from(client)
     refute_nil(pin, 'unable to get pin from Redis connection')
     pin.tracer = @tracer
   end