Adding auto_instruments_ignore config option

This adds a `auto_instruments_ignore` config option so files can be excluded from autoinstruments. By defaut this is an empty array. Example usage: `auto_instruments_ignore: ['application_controller']`.
scoutapp · Sep 23, 2019 · 551f561 · 551f561
1 parent 84575a5
commit 551f561
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Showing 3 changed files with 24 additions and 5 deletions.
diff --git a/lib/scout_apm/auto_instrument/instruction_sequence.rb b/lib/scout_apm/auto_instrument/instruction_sequence.rb
@@ -5,15 +5,17 @@ module ScoutApm
   module AutoInstrument
     module InstructionSequence
       def load_iseq(path)
-        if Rails.controller_path?(path)
+        if Rails.controller_path?(path) & !Rails.ignore?(path)
           begin
             new_code = Rails.rewrite(path)
             return self.compile(new_code, File.basename(path), path)
           rescue
             warn "Failed to apply auto-instrumentation to #{path}: #{$!}"
           end
+        elsif Rails.ignore?(path)
+          warn "AutoInstruments are ignored for path=#{path}."
         end
-        
+
         return self.compile_file(path)
       end
     end

diff --git a/lib/scout_apm/auto_instrument/rails.rb b/lib/scout_apm/auto_instrument/rails.rb
@@ -17,6 +17,19 @@ def self.controller_path? path
         CONTROLLER_FILE.match(path) && !GEM_FILE.match(path)
       end
 
+      # Autoinstruments increases overhead when applied to many code expressions that perform little work.
+      # You can exclude files from autoinstruments via the `auto_instruments_ignore` option.
+      def self.ignore?(path)
+        res = false
+        ScoutApm::Agent.instance.context.config.value('auto_instruments_ignore').each do |ignored_file_name|
+          if path.include?(ignored_file_name)
+            res = true
+            break
+          end
+        end
+        res
+      end
+
       def self.rewrite(path, code = nil)
         code ||= File.read(path)
 

diff --git a/lib/scout_apm/config.rb b/lib/scout_apm/config.rb
@@ -34,6 +34,7 @@
 # start_resque_server_instrument - Used in special situations with certain Resque installs
 # timeline_traces - true/false to enable sending of of the timeline trace format.
 # auto_instruments - true/false whether to install autoinstruments. Only installed if on a supported Ruby version.
+# auto_instruments_ignore - An array of file names to exclude from autoinstruments (Ex: ['application_controller']).
 #
 # Any of these config settings can be set with an environment variable prefixed
 # by SCOUT_ and uppercasing the key: SCOUT_LOG_LEVEL for instance.
@@ -77,7 +78,8 @@ class Config
         'uri_reporting',
         'instrument_http_url_length',
         'timeline_traces',
-        'auto_instruments'
+        'auto_instruments',
+        'auto_instruments_ignore'
     ]
 
     ################################################################################
@@ -171,7 +173,8 @@ def coerce(val)
       'instrument_http_url_length' => IntegerCoercion.new,
       'start_resque_server_instrument' => BooleanCoercion.new,
       'timeline_traces' => BooleanCoercion.new,
-      'auto_instruments' => BooleanCoercion.new
+      'auto_instruments' => BooleanCoercion.new,
+      'auto_instruments_ignore' => JsonCoercion.new,
     }
 
 
@@ -280,7 +283,8 @@ class ConfigDefaults
         'start_resque_server_instrument' => true, # still only starts if Resque is detected
         'collect_remote_ip' => true,
         'timeline_traces' => true,
-        'auto_instruments' => false
+        'auto_instruments' => false,
+        'auto_instruments_ignore' => []
       }.freeze
 
       def value(key)