Upgrade to Rails 6.0 and apply new framework defaults

config/initializers/prometheus.rb

@@ -1,9 +1,13 @@
 # frozen_string_literal: true
 
+require 'code_ocean/config'
+
 return unless CodeOcean::Config.new(:code_ocean).read[:prometheus_exporter][:enabled] && !defined?(::Rails::Console)
 return if %w[db: assets:].any? { |task| Rake.application.top_level_tasks.to_s.include?(task) }
 
 # Add metric callbacks to all models
-ApplicationRecord.include Prometheus::Record
+ActiveSupport.on_load :active_record do
+  include Prometheus::Record
+end
 
 # Initialization is performed in config/application.rb