Implement A/B Test for using AWS as an executor for Java

app/models/submission.rb

@@ -195,7 +195,8 @@ class Submission < ApplicationRecord
   def prepared_runner
     request_time = Time.zone.now
     begin
-      runner = Runner.for(user, exercise.execution_environment)
+      execution_environment = AwsStudy.get_execution_environment(user, exercise)
+      runner = Runner.for(user, execution_environment)
       files = collect_files
       files.reject!(&:teacher_defined_assessment?) if cause == 'run'
       Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Copying files to Runner #{runner.id} for #{user_type} #{user_id} and Submission #{id}." }

lib/aws_study.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class AwsStudy
+  def self.get_for(exercise)
+    java20_collection = ExerciseCollection.find_by(name: 'java2020', id: 11)
+    java20_bonus_collection = ExerciseCollection.find_by(name: 'java2020-bonusexercise', id: 12)
+
+    exercise.exercise_collections.any? {|ec| [java20_collection, java20_bonus_collection].include?(ec) }
+  end
+
+  def self.get_execution_environment(user, exercise)
+    # Poseidon is disabled and thus no AWS support available
+    return exercise.execution_environment unless Runner::Strategy::Poseidon == Runner.strategy_class
+
+    java20_exercise = get_for(exercise)
+    # Exercise is not part of the experiment
+    return exercise.execution_environment unless java20_exercise
+
+    user_group = UserGroupSeparator.get_aws_group(user.id)
+    case user_group
+      when :use_aws
+        # AWS functions are currently identified with their name
+        aws_function = ExecutionEnvironment.find_by(docker_image: 'java11Exec')
+        # Fallback to the default execution environment if no AWS function is found
+        aws_function || exercise.execution_environment
+      else # :no_aws
+        exercise.execution_environment
+    end
+  end
+end

lib/user_group_separator.rb

@@ -32,4 +32,16 @@ class UserGroupSeparator
         :no_community_solution
     end
   end
+
+  # Different user groups for using AWS lambda functions instead of Nomad based on the user_id
+  # This test is independent from any other A/B Test
+  def self.get_aws_group(user_id)
+    user_group = user_id % 2 # => 0, 1
+    case user_group
+      when 0
+        :no_aws
+      else # 1
+        :use_aws
+    end
+  end
 end