diff --git a/app/helpers/host_description_helper.rb b/app/helpers/host_description_helper.rb
index 655dcec5515..b58e1ab3fde 100644
--- a/app/helpers/host_description_helper.rb
+++ b/app/helpers/host_description_helper.rb
@@ -1,5 +1,5 @@
 module HostDescriptionHelper
-  UI.register_host_description do
+  ::UI.register_host_description do
     multiple_actions_provider :base_multiple_actions
     overview_fields_provider :base_status_overview_fields
     overview_fields_provider :base_host_overview_fields
diff --git a/app/models/concerns/foreman/sti.rb b/app/models/concerns/foreman/sti.rb
index 8cc5965ae53..edace2ba1b0 100644
--- a/app/models/concerns/foreman/sti.rb
+++ b/app/models/concerns/foreman/sti.rb
@@ -1,12 +1,12 @@
 module Foreman
   module STI
-    def self.prepended(base)
-      class << base
-        prepend ClassMethods
-      end
+    extend ActiveSupport::Concern
+
+    prepended do
+      cattr_accessor :preloaded, instance_accessor: false
     end
 
-    module ClassMethods
+    class_methods do
       # ensures that the correct STI object is created when :type is passed.
       def new(*attributes, &block)
         if (h = attributes.first).is_a?(Hash) && (type = h.with_indifferent_access.delete(:type)) && !type.empty?
@@ -18,6 +18,33 @@ def new(*attributes, &block)
 
         super
       end
+
+      def descendants
+        preload_sti unless preloaded
+        super
+      end
+
+      # Constantizes all types present in the database. There might be more on
+      # disk, but that does not matter in practice as far as the STI API is
+      # concerned.
+      #
+      # Assumes store_full_sti_class is true, the default.
+      def preload_sti
+        return [] unless base_class.connected? && base_class.table_exists?
+        types_in_db = base_class
+                          .unscoped
+                          .select(inheritance_column)
+                          .distinct
+                          .pluck(inheritance_column)
+                          .compact
+
+        types_in_db.each do |type|
+          logger.debug("Preloading STI type #{type}")
+          type.constantize
+        end
+
+        self.preloaded = true
+      end
     end
 
     def save(*args)
diff --git a/app/models/concerns/nested_ancestry_common.rb b/app/models/concerns/nested_ancestry_common.rb
index 37ee67a3418..276696be868 100644
--- a/app/models/concerns/nested_ancestry_common.rb
+++ b/app/models/concerns/nested_ancestry_common.rb
@@ -102,3 +102,5 @@ def update_matchers
     lookup_values.update_all(:match => "#{obj_type}=#{title}")
   end
 end
+
+require_dependency 'nested_ancestry_common/search'
diff --git a/app/models/hostgroup.rb b/app/models/hostgroup.rb
index a05142c662f..1bb9b013ca5 100644
--- a/app/models/hostgroup.rb
+++ b/app/models/hostgroup.rb
@@ -105,7 +105,7 @@ class Hostgroup < ApplicationRecord
     property :pxe_loader, String, desc: 'Returns boot loader to be applied on each host within this host group'
     property :title, String, desc: 'Returns full title of this host group, e.g. Base/CentOS 7'
   end
-  class Jail < Safemode::Jail
+  class Jail < ::Safemode::Jail
     allow :id, :name, :diskLayout, :puppet_server, :operatingsystem, :architecture,
       :ptable, :url_for_boot, :params, :puppet_proxy, :puppet_ca_server,
       :os, :arch, :domain, :subnet, :subnet6, :hosts, :realm,
diff --git a/app/models/subnet.rb b/app/models/subnet.rb
index 0f53cb2dade..bd2a142f104 100644
--- a/app/models/subnet.rb
+++ b/app/models/subnet.rb
@@ -269,7 +269,7 @@ def external_ipam?
   end
 
   def external_ipam_proxy(attrs = {})
-    @external_ipam_proxy ||= ProxyAPI::ExternalIpam.new({:url => externalipam.url}.merge(attrs)) if external_ipam?
+    @external_ipam_proxy ||= ProxyAPI::ExternalIPAM.new({:url => externalipam.url}.merge(attrs)) if external_ipam?
   end
 
   def ipam?
diff --git a/app/models/taxonomy.rb b/app/models/taxonomy.rb
index 855c667b70a..cd514d39801 100644
--- a/app/models/taxonomy.rb
+++ b/app/models/taxonomy.rb
@@ -51,7 +51,7 @@ def self.inherited(child)
       end
       child.const_set('Jail', jail_class)
     end
-    child.send(:include, NestedAncestryCommon::Search)
+    child.send(:include, ::NestedAncestryCommon::Search)
     super
   end
 
diff --git a/app/registries/foreman/plugin/report_scanner_registry.rb b/app/registries/foreman/plugin/report_scanner_registry.rb
index f6d23479d88..dea79f8e4b1 100644
--- a/app/registries/foreman/plugin/report_scanner_registry.rb
+++ b/app/registries/foreman/plugin/report_scanner_registry.rb
@@ -1,10 +1,8 @@
-require_dependency File.expand_path('../../../services/report_scanner/puppet_report_scanner', __dir__)
-
 module Foreman
   class Plugin
     class ReportScannerRegistry
       DEFAULT_REPORT_SCANNERS = [
-        ::Foreman::PuppetReportScanner,
+        ::Foreman::ReportScanner::PuppetReportScanner,
       ].freeze
 
       attr_accessor :report_scanners
diff --git a/app/registries/foreman/plugin/webpack_assets.rb b/app/registries/foreman/plugin/webpack_assets.rb
deleted file mode 100644
index e69de29bb2d..00000000000
diff --git a/app/services/foreman/report_scanner/puppet_report_scanner.rb b/app/services/foreman/report_scanner/puppet_report_scanner.rb
new file mode 100644
index 00000000000..abcce1b290f
--- /dev/null
+++ b/app/services/foreman/report_scanner/puppet_report_scanner.rb
@@ -0,0 +1,20 @@
+module Foreman
+  module ReportScanner
+    class PuppetReportScanner
+      class << self
+        def identify_origin(report_data)
+          'Puppet' if puppet_report?(report_data['logs'] || [])
+        end
+
+        def add_reporter_data(report, report_data)
+          # no additional data apart of origin
+        end
+
+        def puppet_report?(logs)
+          log = logs.last
+          log && log['log'].fetch('sources', {}).fetch('source', '') =~ /Puppet/
+        end
+      end
+    end
+  end
+end
diff --git a/app/services/ipam.rb b/app/services/ipam.rb
index c5ce22a53b8..36dd6fc52c3 100644
--- a/app/services/ipam.rb
+++ b/app/services/ipam.rb
@@ -6,7 +6,7 @@ def self.new(type, *args)
     when IPAM::MODES[:none]
       IPAM::None.new(*args)
     when IPAM::MODES[:dhcp]
-      IPAM::Dhcp.new(*args)
+      IPAM::DHCP.new(*args)
     when IPAM::MODES[:db]
       IPAM::Db.new(*args)
     when IPAM::MODES[:random_db]
@@ -14,7 +14,7 @@ def self.new(type, *args)
     when IPAM::MODES[:eui64]
       IPAM::Eui64.new(*args)
     when IPAM::MODES[:external_ipam]
-      IPAM::ExternalIpam.new(*args)
+      IPAM::ExternalIPAM.new(*args)
     else
       raise ::Foreman::Exception.new(N_("Unknown IPAM type - can't continue"))
     end
diff --git a/app/services/ipam/dhcp.rb b/app/services/ipam/dhcp.rb
index 8fd08d5d8a5..9f30533eba0 100644
--- a/app/services/ipam/dhcp.rb
+++ b/app/services/ipam/dhcp.rb
@@ -1,5 +1,5 @@
 module IPAM
-  class Dhcp < Base
+  class DHCP < Base
     delegate :dhcp, :dhcp_proxy, :to => :subnet
     def suggest_ip
       unless subnet.dhcp?
diff --git a/app/services/ipam/external_ipam.rb b/app/services/ipam/external_ipam.rb
index bc24b71133f..708d57744c8 100644
--- a/app/services/ipam/external_ipam.rb
+++ b/app/services/ipam/external_ipam.rb
@@ -1,5 +1,5 @@
 module IPAM
-  class ExternalIpam < Base
+  class ExternalIPAM < Base
     delegate :external_ipam_proxy, :to => :subnet
 
     def suggest_ip
diff --git a/app/services/proxy_api/external_ipam.rb b/app/services/proxy_api/external_ipam.rb
index f67431e2da7..22cf637bdd5 100644
--- a/app/services/proxy_api/external_ipam.rb
+++ b/app/services/proxy_api/external_ipam.rb
@@ -1,7 +1,7 @@
 require 'uri'
 
 module ProxyAPI
-  class ExternalIpam < ProxyAPI::Resource
+  class ExternalIPAM < ProxyAPI::Resource
     def initialize(args)
       @url = args[:url] + "/ipam"
       super args
diff --git a/app/services/proxy_status/puppetca.rb b/app/services/proxy_status/puppetca.rb
index c6d6336ffcc..2f812e4dfb0 100644
--- a/app/services/proxy_status/puppetca.rb
+++ b/app/services/proxy_status/puppetca.rb
@@ -1,5 +1,5 @@
 module ProxyStatus
-  class PuppetCA < Base
+  class Puppetca < Base
     def certs
       fetch_proxy_data('/certs') do
         api.all.map do |name, properties|
@@ -71,4 +71,4 @@ def api_class
     end
   end
 end
-ProxyStatus.status_registry.add(ProxyStatus::PuppetCA)
+ProxyStatus.status_registry.add(ProxyStatus::Puppetca)
diff --git a/app/services/report_scanner/puppet_report_scanner.rb b/app/services/report_scanner/puppet_report_scanner.rb
deleted file mode 100644
index 57b75a95d4d..00000000000
--- a/app/services/report_scanner/puppet_report_scanner.rb
+++ /dev/null
@@ -1,18 +0,0 @@
-module Foreman
-  class PuppetReportScanner
-    class << self
-      def identify_origin(report_data)
-        'Puppet' if puppet_report?(report_data['logs'] || [])
-      end
-
-      def add_reporter_data(report, report_data)
-        # no additional data apart of origin
-      end
-
-      def puppet_report?(logs)
-        log = logs.last
-        log && log['log'].fetch('sources', {}).fetch('source', '') =~ /Puppet/
-      end
-    end
-  end
-end
diff --git a/app/services/setting_registry.rb b/app/services/setting_registry.rb
index 17e933f7f00..2d596123fa6 100644
--- a/app/services/setting_registry.rb
+++ b/app/services/setting_registry.rb
@@ -132,18 +132,9 @@ def load_definitions
     end
   end
 
-  def known_categories
-    unless @known_descendants == Setting.descendants
-      @known_descendants = Setting.descendants
-      @known_categories = @known_descendants.map(&:name) << 'Setting'
-      @values_loaded_at = nil # force all values to be reloaded
-    end
-    @known_categories
-  end
-
   def load_values(ignore_cache: false)
     # we are loading only known STIs as we load settings fairly early the first time and plugin classes might not be loaded yet.
-    settings = Setting.unscoped.where(category: known_categories).where.not(value: nil)
+    settings = Setting.unscoped.where(category: 'Setting').where.not(value: nil)
     settings = settings.where('updated_at >= ?', @values_loaded_at) unless ignore_cache || @values_loaded_at.nil?
     settings.each do |s|
       unless (definition = find(s.name))
diff --git a/config/application.rb b/config/application.rb
index 3578f6292e2..0b6da19afad 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -104,7 +104,7 @@ class Application < Rails::Application
     Dir["#{Rails.root}/config/routes/**/*.rb"].each do |route_file|
       config.paths['config/routes.rb'] << route_file
     end
-
+    config.load_defaults 6.0
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.
@@ -115,7 +115,7 @@ class Application < Rails::Application
     config.autoload_paths += %W(#{config.root}/app/models/compute_resources)
     config.autoload_paths += %W(#{config.root}/app/models/fact_names)
     config.autoload_paths += %W(#{config.root}/app/models/lookup_keys)
-    config.autoload_paths += %W(#{config.root}/app/models/host_status)
+    # config.autoload_paths += %W(#{config.root}/app/models/host_status)
     config.autoload_paths += %W(#{config.root}/app/models/operatingsystems)
     config.autoload_paths += %W(#{config.root}/app/models/parameters)
     config.autoload_paths += %W(#{config.root}/app/models/taxonomies)
diff --git a/config/initializers/zeitwerk.rb b/config/initializers/zeitwerk.rb
new file mode 100644
index 00000000000..65eefe48a55
--- /dev/null
+++ b/config/initializers/zeitwerk.rb
@@ -0,0 +1,39 @@
+Rails.autoloaders.main.inflector.inflect(
+  'ui' => 'UI',
+  'proxy_api' => 'ProxyAPI',
+  'sti' => 'STI',
+  'dhcp' => 'DHCP',
+  'dns' => 'DNS',
+  'tftp' => 'TFTP',
+  'external_ipam' => 'ExternalIPAM',
+  'bmc' => 'BMC',
+  'ui_notifications' => 'UINotifications',
+  'ipam' => 'IPAM',
+  'ssh' => 'SSH',
+  'ssh_provision' => 'SSHProvision',
+  'ssh_execution_provider' => 'SSHExecutionProvider',
+  'keep_current_request_id' => 'KeepCurrentRequestID',
+  'ec2' => 'EC2',
+  'aws' => 'AWS',
+  'gce' => 'GCE',
+  'aix' => 'AIX',
+  'nxos' => 'NXOS',
+  'vrp' => 'VRP',
+  'sso' => 'SSO',
+  'puppet_ca_certificate' => 'PuppetCACertificate',
+  'url_resolver' => 'URLResolver',
+  'ztp_record' => 'ZTPRecord',
+  'aaaa_record' => 'AAAARecord',
+  'ptr4_record' => 'PTR4Record',
+  'ptr6_record' => 'PTR6Record'
+)
+
+Rails.autoloaders.main.ignore(
+  Rails.root.join('lib/core_extensions.rb'),
+  Rails.root.join('lib/generators')
+)
+Rails.autoloaders.once.ignore(
+  Rails.root.join('app/registries/foreman/access_permissions.rb'),
+  Rails.root.join('app/registries/foreman/settings.rb'),
+  Rails.root.join('app/registries/foreman/settings')
+)
diff --git a/db/migrate/20140902102858_convert_ipam_to_string.rb b/db/migrate/20140902102858_convert_ipam_to_string.rb
index 881cb82c9d1..d33d3b5c7f3 100644
--- a/db/migrate/20140902102858_convert_ipam_to_string.rb
+++ b/db/migrate/20140902102858_convert_ipam_to_string.rb
@@ -1,6 +1,6 @@
 class ConvertIpamToString < ActiveRecord::Migration[4.2]
   def up
-    change_column :subnets, :ipam, :string, :default => IPAM::MODES[:dhcp], :null => false, :limit => 255
+    change_column :subnets, :ipam, :string, :default => ::IPAM::MODES[:dhcp], :null => false, :limit => 255
   end
 
   def down
diff --git a/test/models/subnet/external_ipam_test.rb b/test/models/subnet/external_ipam_test.rb
index 4130fc618d3..d471ec50b7a 100644
--- a/test/models/subnet/external_ipam_test.rb
+++ b/test/models/subnet/external_ipam_test.rb
@@ -1,6 +1,6 @@
 require 'test_helper'
 
-class Subnet::ExternalIpamTest < ActiveSupport::TestCase
+class Subnet::ExternalIPAMTest < ActiveSupport::TestCase
   test 'external ipam is supported for IPv4' do
     subnet = FactoryBot.build(:subnet_ipv4)
     assert subnet.supports_ipam_mode?(:external_ipam)
diff --git a/test/unit/ipam_test.rb b/test/unit/ipam_test.rb
index 21f13916766..7a3a813aab8 100644
--- a/test/unit/ipam_test.rb
+++ b/test/unit/ipam_test.rb
@@ -9,7 +9,7 @@ class IPAMTest < ActiveSupport::TestCase
       fake_proxy = mock("dhcp_proxy")
       fake_proxy.stubs(:unused_ip => {'ip' => '192.168.1.25'})
       subnet.stubs(:dhcp_proxy => fake_proxy)
-      ipam = IPAM::Dhcp.new(:subnet => subnet, :mac => '00:11:22:33:44:55')
+      ipam = IPAM::DHCP.new(:subnet => subnet, :mac => '00:11:22:33:44:55')
       assert_equal '192.168.1.25', ipam.suggest_ip
     end
   end
diff --git a/test/unit/report_scanner/puppet_report_scanner_test.rb b/test/unit/report_scanner/puppet_report_scanner_test.rb
index 07fd06ca915..9d57305aa9d 100644
--- a/test/unit/report_scanner/puppet_report_scanner_test.rb
+++ b/test/unit/report_scanner/puppet_report_scanner_test.rb
@@ -1,7 +1,7 @@
 require 'test_helper'
 
 class PuppetReportScannerTest < ActiveSupport::TestCase
-  subject { Foreman::PuppetReportScanner }
+  subject { Foreman::ReportScanner::PuppetReportScanner }
 
   describe '.identify_origin' do
     it 'returns Puppet if puppet_report' do