diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 0356df80d..f3c97a4d6 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -36,7 +36,7 @@ jobs:
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 2.6.6
+          ruby-version: 2.7.3
       - name: Increase MySQL max_allowed_packet to 1GB (workaround for unknown/missing service option)
         run: |
           sudo apt-get install -y mysql-client
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d183a7b4f..d2b83ad20 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,5 +1,5 @@
 default:
-  image: registry.znuny.com/docker/zammad-ci:stable
+  image: registry.znuny.com/docker/zammad-ci:test-ruby-3.7
 
 include:
   - local: '/.gitlab/ci/base.yml'
@@ -43,9 +43,9 @@ variables:
 # Cache gems in between jobs and pipelines
 # ATTENTION: We use a combination of the Ruby major and minor version number
 # as a key for the cache to avoid cache growth and incompatibilities between
-# the gems. Search hook: 2.6.6 (change it when updating the Ruby version too)
+# the gems. Search hook: 2.7.2 (change it when updating the Ruby version too)
 cache:
-  key: "centos7ruby266rails6"
+  key: "centos7ruby273"
   paths:
     - vendor/ruby
     # ATTENTION: This should be a dedicated cache only used in the job "TODO".
diff --git a/.gitlab/ci/browser-core/api_client_ruby.yml b/.gitlab/ci/browser-core/api_client_ruby.yml
index b26bfc387..caf7c4499 100644
--- a/.gitlab/ci/browser-core/api_client_ruby.yml
+++ b/.gitlab/ci/browser-core/api_client_ruby.yml
@@ -7,6 +7,7 @@ api_client_ruby:
     - bundle exec rake zammad:ci:test:start
     - git clone https://github.com/zammad/zammad-api-client-ruby.git
     - cd zammad-api-client-ruby
+    - bundle update --bundler
     - bundle install -j $(nproc)
     - bundle exec rspec
 
diff --git a/.gitlab/ci/pre.yml b/.gitlab/ci/pre.yml
index 211cd4531..a8f535ad8 100644
--- a/.gitlab/ci/pre.yml
+++ b/.gitlab/ci/pre.yml
@@ -32,6 +32,17 @@ zeitwerk_check:
     - bundle exec rake zammad:db:init
     - bundle exec rails zeitwerk:check
 
+zeitwerk_check:
+  <<: *template_pre
+  extends:
+    - .tags_docker
+    - .services_postgresql
+  script:
+    - bundle install -j $(nproc) --path vendor
+    - bundle exec ruby script/build/database_config.rb
+    - bundle exec rake zammad:db:init
+    - bundle exec rails zeitwerk:check
+
 coffeelint:
   <<: *template_pre
   script:
diff --git a/.ruby-version b/.ruby-version
index 338a5b5d8..2c9b4ef42 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.6.6
+2.7.3
diff --git a/Gemfile b/Gemfile
index 26af002ce..230ea5810 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,7 +3,7 @@
 source 'https://rubygems.org'
 
 # core - base
-ruby '2.6.6'
+ruby '2.7.3'
 gem 'rails', '6.0.4'
 
 # core - rails additions
@@ -19,7 +19,7 @@ gem 'unicorn', group: :unicorn
 
 # core - supported ORMs
 gem 'activerecord-nulldb-adapter', group: :nulldb
-gem 'mysql2', '0.4.10', group: :mysql
+gem 'mysql2', group: :mysql
 gem 'pg', '0.21.0', group: :postgres
 
 # core - asynchrous task execution
diff --git a/Gemfile.lock b/Gemfile.lock
index 167ea955b..1ed5c8687 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -129,7 +129,7 @@ GEM
     biz (1.8.2)
       clavius (~> 1.0)
       tzinfo
-    bootsnap (1.3.2)
+    bootsnap (1.5.1)
       msgpack (~> 1.0)
     browser (2.5.3)
     buftok (0.2.0)
@@ -296,19 +296,19 @@ GEM
     memoizable (0.4.2)
       thread_safe (~> 0.3, >= 0.3.1)
     method_source (0.9.2)
-    mime-types (3.2.2)
+    mime-types (3.3.1)
       mime-types-data (~> 3.2015)
-    mime-types-data (3.2019.0331)
+    mime-types-data (3.2020.1104)
     mini_mime (1.1.0)
     mini_portile2 (2.5.3)
     mini_racer (0.2.9)
       libv8 (>= 6.9.411)
     minitest (5.14.4)
-    msgpack (1.2.4)
+    msgpack (1.3.3)
     multi_json (1.15.0)
     multi_xml (0.6.0)
     multipart-post (2.1.1)
-    mysql2 (0.4.10)
+    mysql2 (0.5.3)
     naught (1.1.0)
     nenv (0.3.0)
     nestful (1.1.3)
@@ -638,7 +638,7 @@ DEPENDENCIES
   mail!
   mime-types
   mini_racer
-  mysql2 (= 0.4.10)
+  mysql2
   net-ldap
   oauth2
   omniauth-facebook
@@ -699,7 +699,7 @@ DEPENDENCIES
   zendesk_api
 
 RUBY VERSION
-   ruby 2.6.6p146
+   ruby 2.7.3p183
 
 BUNDLED WITH
-   1.17.3
+   2.2.20
diff --git a/app/controllers/knowledge_base/answers_controller.rb b/app/controllers/knowledge_base/answers_controller.rb
index 79720644c..ef4c5ccc7 100644
--- a/app/controllers/knowledge_base/answers_controller.rb
+++ b/app/controllers/knowledge_base/answers_controller.rb
@@ -75,7 +75,7 @@ class KnowledgeBase::AnswersController < KnowledgeBase::BaseController
 
     assets = object.assets({})
 
-    contents = object.translations.map(&:content).compact
+    contents = object.translations.filter_map(&:content)
     assets = ApplicationModel::CanAssets.reduce contents, assets
 
     render json: { id: object.id, assets: assets }, status: :created
diff --git a/app/controllers/links_controller.rb b/app/controllers/links_controller.rb
index 1bc6e9851..8140aed8b 100644
--- a/app/controllers/links_controller.rb
+++ b/app/controllers/links_controller.rb
@@ -12,8 +12,7 @@ class LinksController < ApplicationController
     )
 
     linked_objects = links
-                     .map { |elem| elem['link_object']&.safe_constantize&.lookup(id: elem['link_object_value']) }
-                     .compact
+                     .filter_map { |elem| elem['link_object']&.safe_constantize&.lookup(id: elem['link_object_value']) }
 
     # return result
     render json: {
diff --git a/app/jobs/checks_kb_client_notification_job.rb b/app/jobs/checks_kb_client_notification_job.rb
index 3d92c7be5..9e7e58a21 100644
--- a/app/jobs/checks_kb_client_notification_job.rb
+++ b/app/jobs/checks_kb_client_notification_job.rb
@@ -53,10 +53,8 @@ class ChecksKbClientNotificationJob < ApplicationJob
   def users_for(permission_suffix)
     Sessions
       .sessions
-      .map { |client_id| Sessions.get(client_id)&.dig(:user, 'id') }
-      .compact
-      .map { |user_id| User.find_by(id: user_id) }
-      .compact
+      .filter_map { |client_id| Sessions.get(client_id)&.dig(:user, 'id') }
+      .filter_map { |user_id| User.find_by(id: user_id) }
       .select { |user| user.permissions? "knowledge_base.#{permission_suffix}" }
   end
 
diff --git a/app/models/channel/email_parser.rb b/app/models/channel/email_parser.rb
index 3fedf6ac7..ae388eb76 100644
--- a/app/models/channel/email_parser.rb
+++ b/app/models/channel/email_parser.rb
@@ -377,7 +377,7 @@ returns
 
   def self.sender_attributes(from)
     if from.is_a?(HashWithIndifferentAccess)
-      from = SENDER_FIELDS.map { |f| from[f] }.compact
+      from = SENDER_FIELDS.filter_map { |f| from[f] }
                           .map(&:to_utf8).reject(&:blank?)
                           .partition { |address| address.match?(EMAIL_REGEX) }
                           .flatten.first
@@ -743,7 +743,7 @@ process unprocessable_mails (tmp/unprocessable_mail/*.eml) again
     end
 
     # for some broken sm mail clients (X-MimeOLE: Produced By Microsoft Exchange V6.5)
-    filename ||= file.header[:content_location].to_s.force_encoding('utf-8')
+    filename ||= file.header[:content_location].to_s.dup.force_encoding('utf-8')
 
     file_body = String.new(file.body.to_s)
 
diff --git a/app/models/concerns/checks_client_notification.rb b/app/models/concerns/checks_client_notification.rb
index a67556ef3..1eb61dd73 100644
--- a/app/models/concerns/checks_client_notification.rb
+++ b/app/models/concerns/checks_client_notification.rb
@@ -11,8 +11,7 @@ module ChecksClientNotification
   end
 
   def notify_clients_data(event)
-    class_name = self.class.name
-    class_name.gsub!(%r{::}, '')
+    class_name = self.class.name.gsub(%r{::}, '')
 
     {
       message: {
diff --git a/app/models/cti/log.rb b/app/models/cti/log.rb
index 8097b9985..0ced08b9d 100644
--- a/app/models/cti/log.rb
+++ b/app/models/cti/log.rb
@@ -309,7 +309,7 @@ returns
                    .map { |p| p.slice(:from, :to) }
                    .map(&:values).flatten
                    .pluck(:user_id).compact
-                   .map { |user_id| User.lookup(id: user_id) }.compact
+                   .filter_map { |user_id| User.lookup(id: user_id) }
                    .each.with_object({}) { |user, a| user.assets(a) }
 
       {
diff --git a/app/models/knowledge_base/search.rb b/app/models/knowledge_base/search.rb
index 153a3833a..1d9a201b3 100644
--- a/app/models/knowledge_base/search.rb
+++ b/app/models/knowledge_base/search.rb
@@ -37,7 +37,7 @@ class KnowledgeBase
         es_response = SearchIndexBackend.search(query, name, options)
         es_response = search_es_filter(es_response, query, kb_locales, options) if defined? :search_es_filter
 
-        es_response.map { |item| lookup(id: item[:id]) }.compact
+        es_response.filter_map { |item| lookup(id: item[:id]) }
       end
 
       def search_sql(query, kb_locales, options)
diff --git a/app/models/link.rb b/app/models/link.rb
index c52362215..46bd3c0f2 100644
--- a/app/models/link.rb
+++ b/app/models/link.rb
@@ -230,8 +230,7 @@ class Link < ApplicationModel
 
   def self.reduce_assets(assets, link_references)
     link_items = link_references
-                 .map { |elem| lookup_linked_object(elem) }
-                 .compact
+                 .filter_map { |elem| lookup_linked_object(elem) }
 
     ApplicationModel::CanAssets.reduce(link_items, assets)
   end
diff --git a/app/models/tag/object.rb b/app/models/tag/object.rb
index 1f0a8b193..f96992e99 100644
--- a/app/models/tag/object.rb
+++ b/app/models/tag/object.rb
@@ -12,11 +12,11 @@ lookup by name and create tag item
 =end
 
   def self.lookup_by_name_and_create(name)
-    name.strip!
+    lookup = name.strip
 
-    tag_object = Tag::Object.lookup(name: name)
+    tag_object = Tag::Object.lookup(name: lookup)
     return tag_object if tag_object
 
-    Tag::Object.create(name: name)
+    Tag::Object.create(name: lookup)
   end
 end
diff --git a/lib/core_ext/kernel.rb b/lib/core_ext/kernel.rb
deleted file mode 100644
index 5d6e62f50..000000000
--- a/lib/core_ext/kernel.rb
+++ /dev/null
@@ -1,21 +0,0 @@
-# Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
-
-if Kernel.respond_to?(:open_uri_original_open)
-  module Kernel
-
-    module_function
-
-    # see: https://github.com/ruby/ruby/pull/1675
-    def open(name, *rest, &block)
-      if name.respond_to?(:open) && name.method(:open).parameters.present?
-        name.open(*rest, &block)
-      elsif name.respond_to?(:to_str) &&
-            %r{\A[A-Za-z][A-Za-z0-9+\-.]*://} =~ name &&
-            (uri = URI.parse(name)).respond_to?(:open)
-        uri.open(*rest, &block)
-      else
-        open_uri_original_open(name, *rest, &block)
-      end
-    end
-  end
-end
diff --git a/lib/knowledge_base/menu_item_update_action.rb b/lib/knowledge_base/menu_item_update_action.rb
index 1229006c0..70336d724 100644
--- a/lib/knowledge_base/menu_item_update_action.rb
+++ b/lib/knowledge_base/menu_item_update_action.rb
@@ -83,7 +83,7 @@ class KnowledgeBase
 
     def all_ids_present?
       old_ids = scope.pluck(:id)
-      new_ids = @menu_items_data.map { |elem| elem[:id]&.to_i }.compact
+      new_ids = @menu_items_data.filter_map { |elem| elem[:id]&.to_i }
 
       old_ids.sort == new_ids.sort
     end
diff --git a/lib/ldap/group.rb b/lib/ldap/group.rb
index 2b0ecd424..dce710e89 100644
--- a/lib/ldap/group.rb
+++ b/lib/ldap/group.rb
@@ -136,13 +136,13 @@ class Ldap
     end
 
     def group_user_dns_memberuid(entry)
-      entry[:memberuid].collect do |uid|
+      entry[:memberuid].filter_map do |uid|
         dn = nil
         @ldap.search("(&(uid=#{uid})#{Import::Ldap.config[:user_filter]})", attributes: %w[dn]) do |user|
           dn = user.dn
         end
         dn
-      end.compact
+      end
     end
   end
 end
diff --git a/lib/search_index_backend.rb b/lib/search_index_backend.rb
index 585e40cc6..ba75436f0 100644
--- a/lib/search_index_backend.rb
+++ b/lib/search_index_backend.rb
@@ -261,8 +261,7 @@ remove whole data from index
     end
 
     index
-      .map { |local_index| search_by_index(query, local_index, options) }
-      .compact
+      .filter_map { |local_index| search_by_index(query, local_index, options) }
       .flatten(1)
   end
 
diff --git a/lib/sequencer/unit/exchange/folders/id_path_map.rb b/lib/sequencer/unit/exchange/folders/id_path_map.rb
index 33b303a58..fc66a9a73 100644
--- a/lib/sequencer/unit/exchange/folders/id_path_map.rb
+++ b/lib/sequencer/unit/exchange/folders/id_path_map.rb
@@ -16,13 +16,13 @@ class Sequencer
               ids   = ews_folder_ids
               ids ||= []
 
-              ews_folder.id_folder_map.collect do |id, folder|
+              ews_folder.id_folder_map.filter_map do |id, folder|
                 next if ids.present? && ids.exclude?(id)
                 next if folder.total_count.blank?
                 next if folder.total_count.zero?
 
                 [id, ews_folder.display_path(folder)]
-              end.compact.to_h
+              end.to_h
             end
           end
         end
diff --git a/lib/sequencer/unit/import/common/model/associations/extract.rb b/lib/sequencer/unit/import/common/model/associations/extract.rb
index c900f132b..567671953 100644
--- a/lib/sequencer/unit/import/common/model/associations/extract.rb
+++ b/lib/sequencer/unit/import/common/model/associations/extract.rb
@@ -16,7 +16,7 @@ class Sequencer
 
               def process
                 state.provide(:associations) do
-                  associations.collect do |association|
+                  associations.filter_map do |association|
 
                     logger.debug { "Checking association '#{association}'" }
                     next if !mapped.key?(association)
@@ -30,7 +30,7 @@ class Sequencer
 
                     logger.debug { "Using value of association '#{association}'" }
                     [association, value]
-                  end.compact.to_h
+                  end.to_h
                 end
               end
 
diff --git a/lib/sequencer/unit/import/zendesk/user/groups.rb b/lib/sequencer/unit/import/zendesk/user/groups.rb
index 697adc766..f2c027bb6 100644
--- a/lib/sequencer/unit/import/zendesk/user/groups.rb
+++ b/lib/sequencer/unit/import/zendesk/user/groups.rb
@@ -12,8 +12,7 @@ class Sequencer
             private
 
             def groups
-              remote_ids.map { |remote_id| group_map[remote_id] }
-                        .compact
+              remote_ids.filter_map { |remote_id| group_map[remote_id] }
                         .map { |local_id| ::Group.find(local_id) }
             end