diff --git a/app/models/ci/runner.rb b/app/models/ci/runner.rb
index fd1c457a7ff142cdfffeaeb525ad750454a3d358..730f982a4e1ea9e1e6d520a54ab1583b9bf21b07 100644
--- a/app/models/ci/runner.rb
+++ b/app/models/ci/runner.rb
@@ -28,8 +28,8 @@ class Runner < Ci::ApplicationRecord
         if: ->(token_owner_record) { token_owner_record.owner },
         payload: {
           o: ->(token_owner_record) { token_owner_record.owner.try(:organization_id) },
-          g: ->(token_owner_record) { token_owner_record.group_type? ? token_owner_record.sharding_key_id : nil },
-          p: ->(token_owner_record) { token_owner_record.project_type? ? token_owner_record.sharding_key_id : nil },
+          g: ->(token_owner_record) { token_owner_record.runner_namespaces.first&.namespace_id },
+          p: ->(token_owner_record) { token_owner_record.runner_projects.first&.project_id },
           u: ->(token_owner_record) { token_owner_record.creator_id },
           t: ->(token_owner_record) { token_owner_record.partition_id }
         }
@@ -151,7 +151,6 @@ class Runner < Ci::ApplicationRecord
     scope :created_by_admins, -> { with_creator_id(User.admins.ids) }
 
     scope :with_creator_id, ->(value) { where(creator_id: value) }
-    scope :with_sharding_key, ->(value) { where(sharding_key_id: value) }
 
     scope :belonging_to_group_or_project_descendants, ->(group_id) {
       group_ids = Ci::NamespaceMirror.by_group_and_descendants(group_id).select(:namespace_id)
@@ -242,7 +241,6 @@ class Runner < Ci::ApplicationRecord
     scope :with_api_entity_associations, -> { preload(:creator) }
 
     validate :tag_constraints
-    validates :sharding_key_id, presence: true, unless: :instance_type?
     validates :organization_id, presence: true, on: [:create, :update], unless: :instance_type?
     validates :name, length: { maximum: 256 }, if: :name_changed?
     validates :description, length: { maximum: 1024 }, if: :description_changed?
@@ -251,7 +249,6 @@ class Runner < Ci::ApplicationRecord
     validates :registration_type, presence: true
 
     validate :no_projects, unless: :project_type?
-    validate :no_sharding_key_id, if: :instance_type?
     validate :no_organization_id, if: :instance_type?
     validate :no_groups, unless: :group_type?
     validate :any_project, if: :project_type?
@@ -382,11 +379,6 @@ def assign_to(project, current_user = nil)
 
       begin
         transaction do
-          if projects.id_in(sharding_key_id).empty? && !update_project_id
-            self.errors.add(:assign_to, 'Runner is orphaned and no fallback owner exists')
-            next false
-          end
-
           self.runner_projects << ::Ci::RunnerProject.new(project: project, runner: self)
           self.save!
         end
@@ -550,8 +542,10 @@ def ensure_manager(system_xid)
       # rubocop: disable Performance/ActiveRecordSubtransactionMethods -- This is used only in API endpoints outside of transactions
       RunnerManager.safe_find_or_create_by!(runner_id: id, system_xid: system_xid.to_s) do |m|
         m.runner_type = runner_type
-        m.sharding_key_id = sharding_key_id
         m.organization_id = organization_id
+
+        # Use a bogus sharding_key_id instead of copying a potentially NULL value from the runner
+        m.sharding_key_id = instance_type? ? nil : sharding_key_id || 0
       end
       # rubocop: enable Performance/ActiveRecordSubtransactionMethods
     end
@@ -592,20 +586,6 @@ def fallback_owner_project
       Project.order(projects_added_to_runner_asc).find_by_id(project_ids)
     end
 
-    # Ensure we have a valid sharding_key_id. Logic is similar to the one used in
-    # Ci::Runners::UpdateProjectRunnersOwnerService when a project is deleted
-    def update_project_id
-      project_id = fallback_owner_project&.id
-
-      return if project_id.nil?
-
-      self.clear_memoization(:owner)
-      self.sharding_key_id = project_id
-
-      runner_managers.where(runner_type: :project_type).each_batch { |batch| batch.update_all(sharding_key_id: project_id) }
-      taggings.where(runner_type: :project_type).update_all(sharding_key_id: project_id)
-    end
-
     def compute_token_expiration_instance
       return unless expiration_interval = Gitlab::CurrentSettings.runner_token_expiration_interval
 
@@ -653,10 +633,6 @@ def tag_constraints
       end
     end
 
-    def no_sharding_key_id
-      errors.add(:runner, 'cannot have sharding_key_id assigned') if sharding_key_id
-    end
-
     def no_organization_id
       errors.add(:runner, 'cannot have organization_id assigned') if organization_id
     end
diff --git a/app/models/ci/runner_manager.rb b/app/models/ci/runner_manager.rb
index e82f24127231dc806638437f3cf74ad0c1861e0f..711e9beca5abadba9c92c42f90968fcdeba7235e 100644
--- a/app/models/ci/runner_manager.rb
+++ b/app/models/ci/runner_manager.rb
@@ -55,7 +55,6 @@ class RunnerManager < Ci::ApplicationRecord
     validates :runner, presence: true
     validates :runner_type, presence: true, on: :create
     validates :system_xid, presence: true, length: { maximum: 64 }
-    validates :sharding_key_id, presence: true, on: :create, unless: :instance_type?
     validates :organization_id, presence: true, on: [:create, :update], unless: :instance_type?
     validates :version, length: { maximum: 2048 }
     validates :revision, length: { maximum: 255 }
@@ -65,7 +64,6 @@ class RunnerManager < Ci::ApplicationRecord
     validates :config, json_schema: { filename: 'ci_runner_config' }
     validates :runtime_features, json_schema: { filename: 'ci_runner_runtime_features' }
 
-    validate :no_sharding_key_id, if: :instance_type?
     validate :no_organization_id, if: :instance_type?
 
     cached_attr_reader :version, :revision, :platform, :architecture, :ip_address, :contacted_at,
@@ -193,10 +191,6 @@ def schedule_runner_version_update(new_version)
       Ci::Runners::ProcessRunnerVersionUpdateWorker.perform_async(new_version)
     end
 
-    def no_sharding_key_id
-      errors.add(:runner_manager, 'cannot have sharding_key_id assigned') if sharding_key_id
-    end
-
     def no_organization_id
       errors.add(:runner_manager, 'cannot have organization_id assigned') if organization_id
     end
diff --git a/app/models/ci/runner_tagging.rb b/app/models/ci/runner_tagging.rb
index e7c98b15861b4bf8fe9d27bd1de6cfaa825a7e82..a0db870ff5ed3bf1826f4e475ebef7124053200c 100644
--- a/app/models/ci/runner_tagging.rb
+++ b/app/models/ci/runner_tagging.rb
@@ -19,10 +19,8 @@ class RunnerTagging < Ci::ApplicationRecord
     belongs_to :tag, class_name: 'Ci::Tag', optional: false
 
     validates :runner_type, presence: true
-    validates :sharding_key_id, presence: true, unless: :instance_type?
     validates :organization_id, presence: true, on: [:create, :update], unless: :instance_type?
 
-    validate :no_sharding_key_id, if: :instance_type?
     validate :no_organization_id, if: :instance_type?
 
     scope :scoped_runners, -> do
@@ -37,12 +35,6 @@ def set_runner_type
       self.runner_type = runner.runner_type
     end
 
-    def no_sharding_key_id
-      return if sharding_key_id.nil?
-
-      errors.add(:sharding_key_id, 'instance_type runners must not have a sharding_key_id')
-    end
-
     def no_organization_id
       return if organization_id.nil?
 
diff --git a/app/services/ci/runners/update_project_runners_owner_service.rb b/app/services/ci/runners/update_project_runners_owner_service.rb
deleted file mode 100644
index 508f1eb657adb0f5fa3d29dfe62646d682d7447b..0000000000000000000000000000000000000000
--- a/app/services/ci/runners/update_project_runners_owner_service.rb
+++ /dev/null
@@ -1,70 +0,0 @@
-# frozen_string_literal: true
-
-module Ci
-  module Runners
-    # Service used to recompute runner owners after a project is deleted.
-    class UpdateProjectRunnersOwnerService
-      BATCH_SIZE = 1000
-
-      # @param [Int] project_id: the ID of the deleted project
-      # @param [Int] namespace_id: the ID of the parent namespace of the deleted project
-      def initialize(project_id, namespace_id)
-        @project_id = project_id
-        @organization_id = Namespace.find(namespace_id).organization_id
-      end
-
-      def execute
-        # Since the project was deleted in the 'main' database, let's ensure that the respective
-        # ci_runner_projects join records are also gone (would be handled by LFK otherwise,
-        # but it is a helpful precondition for the service's logic)
-        Ci::RunnerProject.belonging_to_project(project_id).each_batch do |batch|
-          batch.delete_all
-        end
-
-        # rubocop: disable CodeReuse/ActiveRecord -- this query is too specific to generalize on the models
-        runner_projects =
-          Ci::RunnerProject.where(Ci::RunnerProject.arel_table[:runner_id].eq(Ci::Runner.arel_table[:id]))
-        orphaned_runners = Ci::Runner.project_type.with_sharding_key(project_id)
-
-        orphaned_runners.select(:id).each_batch(of: BATCH_SIZE) do |batch|
-          runners_missing_owner_project = Ci::Runner.id_in(batch.limit(BATCH_SIZE).pluck_primary_key)
-          runners_with_fallback_owner = runners_missing_owner_project.where_exists(runner_projects.limit(1))
-
-          Ci::Runner.transaction do
-            runner_ids = runners_with_fallback_owner.limit(BATCH_SIZE).pluck_primary_key
-
-            runners_with_fallback_owner.update_all(runner_id_update_query(Ci::Runner.arel_table[:id]))
-            Ci::RunnerManager.project_type.for_runner(runner_ids)
-              .update_all(runner_id_update_query(Ci::RunnerManager.arel_table[:runner_id]))
-            Ci::RunnerTagging.project_type.for_runner(runner_ids)
-              .update_all(runner_id_update_query(Ci::RunnerTagging.arel_table[:runner_id]))
-
-            # Delete any orphaned runners that are still pointing to the project
-            #   (they are the ones which no longer have any matching ci_runner_projects records)
-            # We can afford to sidestep Ci::Runner hooks since we know by definition that
-            # there are no Ci::RunnerProject models pointing to these runners (it's the reason they are being deleted)
-            runners_missing_owner_project.project_type.with_sharding_key(project_id).delete_all
-          end
-        end
-        # rubocop: enable CodeReuse/ActiveRecord
-
-        ServiceResponse.success
-      end
-
-      private
-
-      attr_reader :project_id
-
-      def runner_id_update_query(runner_id_column)
-        # rubocop: disable CodeReuse/ActiveRecord -- this query is too specific to generalize on the models
-        runner_projects = Ci::RunnerProject.where(Ci::RunnerProject.arel_table[:runner_id].eq(runner_id_column))
-
-        <<~SQL
-          sharding_key_id = (#{runner_projects.order(id: :asc).limit(1).select(:project_id).to_sql}),
-          organization_id = #{@organization_id}
-        SQL
-        # rubocop: enable CodeReuse/ActiveRecord
-      end
-    end
-  end
-end
diff --git a/app/workers/all_queues.yml b/app/workers/all_queues.yml
index c2eea937f9e0621c48a2e7303f84172422321282..fa404b479c07f56ee00548bf5900332a839a1781 100644
--- a/app/workers/all_queues.yml
+++ b/app/workers/all_queues.yml
@@ -3497,16 +3497,6 @@
   :idempotent: true
   :tags: []
   :queue_namespace:
-- :name: ci_runners_update_project_runners_owner
-  :worker_name: Ci::Runners::UpdateProjectRunnersOwnerWorker
-  :feature_category: :runner
-  :has_external_dependencies: false
-  :urgency: :low
-  :resource_boundary: :unknown
-  :weight: 1
-  :idempotent: true
-  :tags: []
-  :queue_namespace:
 - :name: ci_safe_disable_pipeline_variables
   :worker_name: Ci::SafeDisablePipelineVariablesWorker
   :feature_category: :ci_variables
diff --git a/app/workers/ci/runners/update_project_runners_owner_worker.rb b/app/workers/ci/runners/update_project_runners_owner_worker.rb
deleted file mode 100644
index 8399d77255b1dc000a7ee42ba908c391f23fbe84..0000000000000000000000000000000000000000
--- a/app/workers/ci/runners/update_project_runners_owner_worker.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-# frozen_string_literal: true
-
-module Ci
-  module Runners
-    class UpdateProjectRunnersOwnerWorker
-      include Gitlab::EventStore::Subscriber
-
-      data_consistency :sticky
-
-      idempotent!
-
-      feature_category :runner
-
-      def handle_event(event)
-        ::Ci::Runners::UpdateProjectRunnersOwnerService.new(event.data[:project_id], event.data[:namespace_id]).execute
-      end
-    end
-  end
-end
diff --git a/config/sidekiq_queues.yml b/config/sidekiq_queues.yml
index 43e05fba35394aa943e2422822cbf2e448cd35e5..1fb65b9c04909177ca59b0c8cfdbc90800fc2570 100644
--- a/config/sidekiq_queues.yml
+++ b/config/sidekiq_queues.yml
@@ -235,8 +235,6 @@
   - 1
 - - ci_runners_process_runner_version_update
   - 1
-- - ci_runners_update_project_runners_owner
-  - 1
 - - ci_safe_disable_pipeline_variables
   - 1
 - - ci_slsa_publish_statement
diff --git a/db/migrate/20250723124358_remove_sharding_key_check_constraint_from_ci_runners2.rb b/db/migrate/20250723124358_remove_sharding_key_check_constraint_from_ci_runners2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..66ea5786d652d8840bada5c16597e16f086d5277
--- /dev/null
+++ b/db/migrate/20250723124358_remove_sharding_key_check_constraint_from_ci_runners2.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class RemoveShardingKeyCheckConstraintFromCiRunners2 < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.3'
+
+  CONSTRAINT_NAME = 'check_sharding_key_id_nullness'
+
+  def up
+    remove_check_constraint(:instance_type_ci_runners, CONSTRAINT_NAME)
+    remove_check_constraint(:group_type_ci_runners, CONSTRAINT_NAME)
+    remove_check_constraint(:project_type_ci_runners, CONSTRAINT_NAME)
+  end
+
+  def down
+    add_check_constraint(:instance_type_ci_runners, 'sharding_key_id IS NULL', CONSTRAINT_NAME)
+    add_check_constraint(:group_type_ci_runners, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+    add_check_constraint(:project_type_ci_runners, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+  end
+end
diff --git a/db/migrate/20250723124360_remove_sharding_key_check_constraint_from_ci_runner_machines2.rb b/db/migrate/20250723124360_remove_sharding_key_check_constraint_from_ci_runner_machines2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..dcba8500b5847f6a4fab73aefafb172b5c7f3e4f
--- /dev/null
+++ b/db/migrate/20250723124360_remove_sharding_key_check_constraint_from_ci_runner_machines2.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class RemoveShardingKeyCheckConstraintFromCiRunnerMachines2 < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.3'
+
+  CONSTRAINT_NAME = 'check_sharding_key_id_nullness'
+
+  def up
+    remove_check_constraint(:instance_type_ci_runner_machines, CONSTRAINT_NAME)
+    remove_check_constraint(:group_type_ci_runner_machines, CONSTRAINT_NAME)
+    remove_check_constraint(:project_type_ci_runner_machines, CONSTRAINT_NAME)
+  end
+
+  def down
+    add_check_constraint(:instance_type_ci_runner_machines, 'sharding_key_id IS NULL', CONSTRAINT_NAME)
+    add_check_constraint(:group_type_ci_runner_machines, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+    add_check_constraint(:project_type_ci_runner_machines, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+  end
+end
diff --git a/db/migrate/20250723124365_remove_sharding_key_check_constraint_from_ci_runner_taggings2.rb b/db/migrate/20250723124365_remove_sharding_key_check_constraint_from_ci_runner_taggings2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..e7cf35667d5b6ef5203d7838f5f33b2555ab4b90
--- /dev/null
+++ b/db/migrate/20250723124365_remove_sharding_key_check_constraint_from_ci_runner_taggings2.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class RemoveShardingKeyCheckConstraintFromCiRunnerTaggings2 < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.3'
+
+  CONSTRAINT_NAME = 'check_sharding_key_id_nullness'
+
+  def up
+    remove_check_constraint(:ci_runner_taggings_instance_type, CONSTRAINT_NAME)
+    remove_check_constraint(:ci_runner_taggings_group_type, CONSTRAINT_NAME)
+    remove_check_constraint(:ci_runner_taggings_project_type, CONSTRAINT_NAME)
+  end
+
+  def down
+    add_check_constraint(:ci_runner_taggings_instance_type, 'sharding_key_id IS NULL', CONSTRAINT_NAME)
+    add_check_constraint(:ci_runner_taggings_group_type, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+    add_check_constraint(:ci_runner_taggings_project_type, 'sharding_key_id IS NOT NULL', CONSTRAINT_NAME)
+  end
+end
diff --git a/db/migrate/20250723124370_cleanup_records_with_null_sharding_key_id_values_from_ci_runners2.rb b/db/migrate/20250723124370_cleanup_records_with_null_sharding_key_id_values_from_ci_runners2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..fec1a7a5f5561e1f6947f3ec5ab955964192fc3f
--- /dev/null
+++ b/db/migrate/20250723124370_cleanup_records_with_null_sharding_key_id_values_from_ci_runners2.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class CleanupRecordsWithNullShardingKeyIdValuesFromCiRunners2 < Gitlab::Database::Migration[2.3]
+  milestone '18.3'
+
+  disable_ddl_transaction!
+  restrict_gitlab_migration gitlab_schema: :gitlab_ci
+
+  BATCH_SIZE = 1000
+
+  class CiRunner < MigrationRecord
+    include EachBatch
+
+    self.table_name = 'ci_runners'
+    self.primary_key = :id
+  end
+
+  def up
+    # no-op - this migration is required to allow a rollback of `RemoveShardingKeyCheckConstraintFromCiRunners2`
+  end
+
+  def down
+    CiRunner.each_batch(of: BATCH_SIZE) do |relation|
+      relation.where.not(runner_type: 1).where(sharding_key_id: nil).delete_all
+    end
+  end
+end
diff --git a/db/migrate/20250723124375_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_machines2.rb b/db/migrate/20250723124375_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_machines2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..4f7df93fdfb7c8a54fa47b658f1368b4366f4355
--- /dev/null
+++ b/db/migrate/20250723124375_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_machines2.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class CleanupRecordsWithNullShardingKeyIdValuesFromCiRunnerMachines2 < Gitlab::Database::Migration[2.3]
+  milestone '18.3'
+
+  disable_ddl_transaction!
+  restrict_gitlab_migration gitlab_schema: :gitlab_ci
+
+  BATCH_SIZE = 1000
+
+  class CiRunnerMachine < MigrationRecord
+    include EachBatch
+
+    self.table_name = 'ci_runner_machines'
+    self.primary_key = :id
+  end
+
+  def up
+    # no-op - this migration is required to allow a rollback of `RemoveShardingKeyCheckConstraintFromCiRunnerMachines2`
+  end
+
+  def down
+    CiRunnerMachine.each_batch(of: BATCH_SIZE) do |relation|
+      relation.where.not(runner_type: 1).where(sharding_key_id: nil).delete_all
+    end
+  end
+end
diff --git a/db/migrate/20250723124378_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_taggings2.rb b/db/migrate/20250723124378_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_taggings2.rb
new file mode 100644
index 0000000000000000000000000000000000000000..df9a7e98aff54235b9de0bbf59202af9ebbd9808
--- /dev/null
+++ b/db/migrate/20250723124378_cleanup_records_with_null_sharding_key_id_values_from_ci_runner_taggings2.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class CleanupRecordsWithNullShardingKeyIdValuesFromCiRunnerTaggings2 < Gitlab::Database::Migration[2.3]
+  milestone '18.3'
+
+  disable_ddl_transaction!
+  restrict_gitlab_migration gitlab_schema: :gitlab_ci
+
+  BATCH_SIZE = 1000
+
+  class CiRunnerTagging < MigrationRecord
+    include EachBatch
+
+    self.table_name = 'ci_runner_taggings'
+    self.primary_key = :id
+  end
+
+  def up
+    # no-op - this migration is required to allow a rollback of `RemoveShardingKeyCheckConstraintFromCiRunnerTaggings2`
+  end
+
+  def down
+    CiRunnerTagging.each_batch(of: BATCH_SIZE) do |relation|
+      relation.where.not(runner_type: 1).where(sharding_key_id: nil).delete_all
+    end
+  end
+end
diff --git a/db/schema_migrations/20250723124358 b/db/schema_migrations/20250723124358
new file mode 100644
index 0000000000000000000000000000000000000000..5fa791eaeb4cc2b7a5d5a5e36a2dc046068e12a7
--- /dev/null
+++ b/db/schema_migrations/20250723124358
@@ -0,0 +1 @@
+e49af8ec9ef7b23170c598e7a60f4ceea457aac175aca234d094fae3f21dd29d
\ No newline at end of file
diff --git a/db/schema_migrations/20250723124360 b/db/schema_migrations/20250723124360
new file mode 100644
index 0000000000000000000000000000000000000000..59503ef03e4b99f83fa6ba8840fc8171c57ad504
--- /dev/null
+++ b/db/schema_migrations/20250723124360
@@ -0,0 +1 @@
+a38f040182f01b28cdb7c77671e1eba6bbbe32e06b73096ec868325af8392e3e
\ No newline at end of file
diff --git a/db/schema_migrations/20250723124365 b/db/schema_migrations/20250723124365
new file mode 100644
index 0000000000000000000000000000000000000000..e0e625d198ecc88b7d83ac02b399396065135583
--- /dev/null
+++ b/db/schema_migrations/20250723124365
@@ -0,0 +1 @@
+5a11a0fc43981e5c904359a89919cbcd313f84e32566e8478415e9d118d7d7b7
\ No newline at end of file
diff --git a/db/schema_migrations/20250723124370 b/db/schema_migrations/20250723124370
new file mode 100644
index 0000000000000000000000000000000000000000..3f85b59fd12b3a73dbae813bb56b751bdf6e3102
--- /dev/null
+++ b/db/schema_migrations/20250723124370
@@ -0,0 +1 @@
+8a6e782b40701b8016df275b3df04f8f8f2a8a3817ca446e3775e82f4b154fa3
\ No newline at end of file
diff --git a/db/schema_migrations/20250723124375 b/db/schema_migrations/20250723124375
new file mode 100644
index 0000000000000000000000000000000000000000..ca7c6810487c1703cbefd8864d1cfe80c2b9cce1
--- /dev/null
+++ b/db/schema_migrations/20250723124375
@@ -0,0 +1 @@
+3ef0cced2f559be303aa83891083d8ca58d52bc0e50bfcdb22c81f6963074cf2
\ No newline at end of file
diff --git a/db/schema_migrations/20250723124378 b/db/schema_migrations/20250723124378
new file mode 100644
index 0000000000000000000000000000000000000000..3513788a3ca1d4e5455e7bcd01a173296fb184b1
--- /dev/null
+++ b/db/schema_migrations/20250723124378
@@ -0,0 +1 @@
+4ab0dcde38c8580cb16500a22c89ca4f31d7680774f56617320be4df8fc5ebad
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index d6194940ab8aefa9c1714281d3672b3446f34464..e57b879d7320b84031ec939b2076af78bf65828c 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -12312,8 +12312,7 @@ CREATE TABLE ci_runner_taggings_group_type (
     runner_id bigint NOT NULL,
     sharding_key_id bigint,
     runner_type smallint NOT NULL,
-    organization_id bigint,
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    organization_id bigint
 );
 
 CREATE SEQUENCE ci_runner_taggings_id_seq
@@ -12331,8 +12330,7 @@ CREATE TABLE ci_runner_taggings_instance_type (
     runner_id bigint NOT NULL,
     sharding_key_id bigint,
     runner_type smallint NOT NULL,
-    organization_id bigint,
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NULL))
+    organization_id bigint
 );
 
 CREATE TABLE ci_runner_taggings_project_type (
@@ -12341,8 +12339,7 @@ CREATE TABLE ci_runner_taggings_project_type (
     runner_id bigint NOT NULL,
     sharding_key_id bigint,
     runner_type smallint NOT NULL,
-    organization_id bigint,
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    organization_id bigint
 );
 
 CREATE TABLE ci_runner_versions (
@@ -15738,8 +15735,7 @@ CREATE TABLE group_type_ci_runner_machines (
     CONSTRAINT check_7dc4eee8a5 CHECK ((char_length(version) <= 2048)),
     CONSTRAINT check_b1e456641b CHECK ((char_length(ip_address) <= 1024)),
     CONSTRAINT check_c788f4b18a CHECK ((char_length(platform) <= 255)),
-    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255))
 );
 
 CREATE TABLE group_type_ci_runners (
@@ -15772,8 +15768,7 @@ CREATE TABLE group_type_ci_runners (
     CONSTRAINT check_1f8618ab23 CHECK ((char_length(name) <= 256)),
     CONSTRAINT check_24b281f5bf CHECK ((char_length(maintainer_note) <= 1024)),
     CONSTRAINT check_5db8ae9d30 CHECK ((char_length(description) <= 1024)),
-    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128))
 );
 
 CREATE TABLE group_wiki_repositories (
@@ -16413,8 +16408,7 @@ CREATE TABLE instance_type_ci_runner_machines (
     CONSTRAINT check_7dc4eee8a5 CHECK ((char_length(version) <= 2048)),
     CONSTRAINT check_b1e456641b CHECK ((char_length(ip_address) <= 1024)),
     CONSTRAINT check_c788f4b18a CHECK ((char_length(platform) <= 255)),
-    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NULL))
+    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255))
 );
 
 CREATE TABLE instance_type_ci_runners (
@@ -16447,8 +16441,7 @@ CREATE TABLE instance_type_ci_runners (
     CONSTRAINT check_1f8618ab23 CHECK ((char_length(name) <= 256)),
     CONSTRAINT check_24b281f5bf CHECK ((char_length(maintainer_note) <= 1024)),
     CONSTRAINT check_5db8ae9d30 CHECK ((char_length(description) <= 1024)),
-    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NULL))
+    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128))
 );
 
 CREATE TABLE integrations (
@@ -22147,8 +22140,7 @@ CREATE TABLE project_type_ci_runner_machines (
     CONSTRAINT check_7dc4eee8a5 CHECK ((char_length(version) <= 2048)),
     CONSTRAINT check_b1e456641b CHECK ((char_length(ip_address) <= 1024)),
     CONSTRAINT check_c788f4b18a CHECK ((char_length(platform) <= 255)),
-    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    CONSTRAINT check_f3d25ab844 CHECK ((char_length(architecture) <= 255))
 );
 
 CREATE TABLE project_type_ci_runners (
@@ -22181,8 +22173,7 @@ CREATE TABLE project_type_ci_runners (
     CONSTRAINT check_1f8618ab23 CHECK ((char_length(name) <= 256)),
     CONSTRAINT check_24b281f5bf CHECK ((char_length(maintainer_note) <= 1024)),
     CONSTRAINT check_5db8ae9d30 CHECK ((char_length(description) <= 1024)),
-    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128)),
-    CONSTRAINT check_sharding_key_id_nullness CHECK ((sharding_key_id IS NOT NULL))
+    CONSTRAINT check_af25130d5a CHECK ((char_length(token) <= 128))
 );
 
 CREATE TABLE project_uploads (
diff --git a/lib/gitlab/event_store.rb b/lib/gitlab/event_store.rb
index f20ab0c44627b478ff57ce27a280df714f9d2e25..83286c288a09ffbd504271885eb51d6392ca7f78 100644
--- a/lib/gitlab/event_store.rb
+++ b/lib/gitlab/event_store.rb
@@ -42,7 +42,6 @@ def configure!(store)
 
         store.subscribe ::MergeRequests::UpdateHeadPipelineWorker, to: ::Ci::PipelineCreatedEvent
         store.subscribe ::Namespaces::UpdateRootStatisticsWorker, to: ::Projects::ProjectDeletedEvent
-        store.subscribe ::Ci::Runners::UpdateProjectRunnersOwnerWorker, to: ::Projects::ProjectDeletedEvent
 
         store.subscribe ::MergeRequests::ProcessAutoMergeFromEventWorker,
           to: ::MergeRequests::AutoMerge::TitleDescriptionUpdateEvent
diff --git a/spec/db/schema_spec.rb b/spec/db/schema_spec.rb
index 94de75e8d41e5e4da84585f5c7ef79d5214210ae..e4da19afbfabcc6c0ff4f82c7974a0ef7abde4b4 100644
--- a/spec/db/schema_spec.rb
+++ b/spec/db/schema_spec.rb
@@ -85,18 +85,18 @@
       ci_resources: %w[project_id],
       p_ci_pipelines: %w[partition_id auto_canceled_by_partition_id auto_canceled_by_id trigger_id],
       p_ci_runner_machine_builds: %w[project_id],
-      ci_runner_taggings: %w[runner_id organization_id sharding_key_id], # The organization_id/sharding_key_id values are meant to populate the partitioned table, no other usage. The runner_id FK exists at the partition level
-      ci_runner_taggings_instance_type: %w[tag_id organization_id sharding_key_id], # organization_id/sharding_key_id are always NULL in this partition, tag_id is handled on ci_runner_taggings
-      ci_runner_taggings_group_type: %w[tag_id organization_id], # tag_id is handled on ci_runner_taggings. These records are indirectly deleted by the FK to group_type_ci_runners
-      ci_runner_taggings_project_type: %w[tag_id organization_id], # tag_id is handled on ci_runner_taggings. These records are indirectly deleted by the FK to project_type_ci_runners
-      ci_runners: %w[sharding_key_id], # This value is meant to populate the partitioned table, no other usage
-      instance_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table.
-      group_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table.
-      project_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table.
-      ci_runner_machines: %w[runner_id organization_id sharding_key_id], # The runner_id and sharding_key_id fields are only used in the partitions, and have the appropriate FKs. The runner_id field will be removed with https://gitlab.com/gitlab-org/gitlab/-/issues/503749.
-      instance_type_ci_runner_machines: %w[organization_id sharding_key_id], # This field is always NULL in this partition.
-      group_type_ci_runner_machines: %w[organization_id sharding_key_id], # No need for LFK, rows will be deleted by the FK to ci_runners.
-      project_type_ci_runner_machines: %w[organization_id sharding_key_id], # No need for LFK, rows will be deleted by the FK to ci_runners.
+      ci_runner_taggings: %w[runner_id organization_id sharding_key_id], # The organization_id value is meant to populate the partitioned table, no other usage. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650. The runner_id FK exists at the partition level
+      ci_runner_taggings_instance_type: %w[tag_id organization_id sharding_key_id], # organization_id is always NULL in this partition, tag_id is handled on ci_runner_taggings. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650
+      ci_runner_taggings_group_type: %w[tag_id organization_id sharding_key_id], # tag_id is handled on ci_runner_taggings. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650. These records are indirectly deleted by the FK to group_type_ci_runners
+      ci_runner_taggings_project_type: %w[tag_id organization_id sharding_key_id], # tag_id is handled on ci_runner_taggings. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650. These records are indirectly deleted by the FK to project_type_ci_runners
+      ci_runners: %w[sharding_key_id], # The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      instance_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      group_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      project_type_ci_runners: %w[creator_id organization_id sharding_key_id], # No need for LFKs on partition, already handled on ci_runners routing table. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      ci_runner_machines: %w[runner_id organization_id sharding_key_id], # The organization_id field is only used in the partitions, and have the appropriate FKs. The runner_id field will be removed with https://gitlab.com/gitlab-org/gitlab/-/issues/503749. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      instance_type_ci_runner_machines: %w[organization_id sharding_key_id], # This field is always NULL in this partition. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      group_type_ci_runner_machines: %w[organization_id sharding_key_id], # No need for LFK, rows will be deleted by the FK to ci_runners. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
+      project_type_ci_runner_machines: %w[organization_id sharding_key_id], # No need for LFK, rows will be deleted by the FK to ci_runners. The sharding_key_id will be dropped in https://gitlab.com/gitlab-org/gitlab/-/issues/547650.
       ci_runner_projects: %w[runner_id],
       ci_sources_pipelines: %w[partition_id source_partition_id source_job_id],
       ci_sources_projects: %w[partition_id],
diff --git a/spec/lib/gitlab/database/sharding_key_spec.rb b/spec/lib/gitlab/database/sharding_key_spec.rb
index 393e8dd779836a2696a5458e0328dae3b50ca4a0..c266149e34f7e10d41c1ccd3fc96d69fba0b1104 100644
--- a/spec/lib/gitlab/database/sharding_key_spec.rb
+++ b/spec/lib/gitlab/database/sharding_key_spec.rb
@@ -35,30 +35,30 @@
 
   # The following tables are work in progress as part of
   # https://gitlab.com/gitlab-org/gitlab/-/issues/398199
-  # TODO: Remove these excepttions once the issue is closed.
+  # TODO: Remove these exceptions once the issue is closed.
   let(:uploads_and_partitions) do
-    [
-      "achievement_uploads.namespace_id",
-      "ai_vectorizable_file_uploads.project_id",
-      "alert_management_alert_metric_image_uploads.project_id",
-      "bulk_import_export_upload_uploads.project_id", "bulk_import_export_upload_uploads.namespace_id",
-      "dependency_list_export_part_uploads.organization_id",
-      "dependency_list_export_uploads.organization_id", "dependency_list_export_uploads.namespace_id",
-      "dependency_list_export_uploads.project_id",
-      "design_management_action_uploads.namespace_id",
-      "import_export_upload_uploads.project_id", "import_export_upload_uploads.namespace_id",
-      "issuable_metric_image_uploads.namespace_id",
-      "namespace_uploads.namespace_id",
-      "note_uploads.namespace_id",
-      "organization_detail_uploads.organization_id",
-      "project_import_export_relation_export_upload_uploads.project_id",
-      "project_topic_uploads.organization_id",
-      "project_uploads.project_id",
-      "snippet_uploads.organization_id",
-      "vulnerability_export_part_uploads.organization_id",
-      "vulnerability_export_uploads.organization_id",
-      "vulnerability_archive_export_uploads.project_id",
-      "vulnerability_remediation_uploads.project_id"
+    %w[
+      achievement_uploads.namespace_id
+      ai_vectorizable_file_uploads.project_id
+      alert_management_alert_metric_image_uploads.project_id
+      bulk_import_export_upload_uploads.project_id bulk_import_export_upload_uploads.namespace_id
+      dependency_list_export_part_uploads.organization_id
+      dependency_list_export_uploads.organization_id dependency_list_export_uploads.namespace_id
+      dependency_list_export_uploads.project_id
+      design_management_action_uploads.namespace_id
+      import_export_upload_uploads.project_id import_export_upload_uploads.namespace_id
+      issuable_metric_image_uploads.namespace_id
+      namespace_uploads.namespace_id
+      note_uploads.namespace_id
+      organization_detail_uploads.organization_id
+      project_import_export_relation_export_upload_uploads.project_id
+      project_topic_uploads.organization_id
+      project_uploads.project_id
+      snippet_uploads.organization_id
+      vulnerability_export_part_uploads.organization_id
+      vulnerability_export_uploads.organization_id
+      vulnerability_archive_export_uploads.project_id
+      vulnerability_remediation_uploads.project_id
     ]
   end
 
diff --git a/spec/models/ci/runner_manager_spec.rb b/spec/models/ci/runner_manager_spec.rb
index 12b9ebd92080a25e30ab3eb7aef1ad68f31ee3fe..700260eae305e4e46dfc7ef9511d6a07d40ca052 100644
--- a/spec/models/ci/runner_manager_spec.rb
+++ b/spec/models/ci/runner_manager_spec.rb
@@ -22,7 +22,6 @@
     it { is_expected.to validate_presence_of(:system_xid) }
     it { is_expected.to validate_length_of(:system_xid).is_at_most(64) }
     it { is_expected.to validate_presence_of(:runner_type).on(:create) }
-    it { is_expected.to validate_presence_of(:sharding_key_id).on(:create) }
     it { is_expected.to validate_presence_of(:organization_id).on([:create, :update]) }
     it { is_expected.to validate_length_of(:version).is_at_most(2048) }
     it { is_expected.to validate_length_of(:revision).is_at_most(255) }
@@ -35,18 +34,6 @@
 
       it { expect(runner_manager).to be_valid }
 
-      context 'when sharding_key_id is present' do
-        let(:runner_manager) do
-          build(:ci_runner_machine, runner: build(:ci_runner, sharding_key_id: non_existing_record_id))
-        end
-
-        it 'is invalid' do
-          expect(runner_manager).to be_invalid
-          expect(runner_manager.errors.full_messages).to contain_exactly(
-            'Runner manager cannot have sharding_key_id assigned')
-        end
-      end
-
       context 'when organization_id is present' do
         let(:runner_manager) do
           build(:ci_runner_machine, runner: build(:ci_runner, organization_id: non_existing_record_id))
@@ -76,60 +63,6 @@
       end
     end
 
-    describe 'shading_key_id validations' do
-      let(:runner_manager) { build(:ci_runner_machine, runner: runner) }
-
-      context 'with instance runner' do
-        let(:runner) { build(:ci_runner, :instance) }
-
-        it { expect(runner).to be_valid }
-
-        context 'when sharding_key_id is not present' do
-          before do
-            runner.sharding_key_id = nil
-            runner_manager.sharding_key_id = nil
-          end
-
-          it { expect(runner_manager).to be_valid }
-        end
-      end
-
-      context 'with group runner' do
-        let(:runner) { build(:ci_runner, :group, groups: [group]) }
-
-        it { expect(runner_manager).to be_valid }
-
-        context 'when sharding_key_id is not present' do
-          before do
-            runner.sharding_key_id = nil
-            runner_manager.sharding_key_id = nil
-          end
-
-          it 'adds error to model', :aggregate_failures do
-            expect(runner_manager).not_to be_valid
-            expect(runner_manager.errors[:sharding_key_id]).to contain_exactly("can't be blank")
-          end
-        end
-      end
-
-      context 'with project runner' do
-        let(:runner) { build(:ci_runner, :project, projects: [project]) }
-
-        it { expect(runner).to be_valid }
-
-        context 'when sharding_key_id is not present' do
-          before do
-            runner.sharding_key_id = nil
-          end
-
-          it 'adds error to model', :aggregate_failures do
-            expect(runner_manager).not_to be_valid
-            expect(runner_manager.errors[:sharding_key_id]).to contain_exactly("can't be blank")
-          end
-        end
-      end
-    end
-
     context 'when runner has runtime features' do
       it 'is valid' do
         runner_manager = build(:ci_runner_machine, runtime_features: { cancelable: true })
diff --git a/spec/models/ci/runner_spec.rb b/spec/models/ci/runner_spec.rb
index 3eb01b9cc43cd8bc93e2e07ebf6718770dd347c0..755d3cc7a2c8bda7a11f62c44fe5b107d192377c 100644
--- a/spec/models/ci/runner_spec.rb
+++ b/spec/models/ci/runner_spec.rb
@@ -127,7 +127,6 @@
     it { is_expected.to validate_presence_of(:access_level) }
     it { is_expected.to validate_presence_of(:runner_type) }
     it { is_expected.to validate_presence_of(:registration_type) }
-    it { is_expected.to validate_presence_of(:sharding_key_id) }
     it { is_expected.to validate_presence_of(:organization_id).on([:create, :update]) }
 
     context 'when runner is instance type' do
@@ -135,15 +134,6 @@
 
       it { expect(runner).to be_valid }
 
-      context 'when sharding_key_id is present' do
-        let(:runner) { build(:ci_runner, :instance_type, sharding_key_id: non_existing_record_id) }
-
-        it 'is invalid' do
-          expect(runner).to be_invalid
-          expect(runner.errors.full_messages).to contain_exactly('Runner cannot have sharding_key_id assigned')
-        end
-      end
-
       context 'when organization_id is present' do
         let(:runner) { build(:ci_runner, :instance_type, organization_id: non_existing_record_id) }
 
@@ -1614,7 +1604,7 @@ def expect_db_update
 
     shared_examples 'a group runner encrypted token' do |prefix|
       let(:runner_type) { :group_type }
-      let(:attrs) { { groups: [group], sharding_key_id: group.id } }
+      let(:attrs) { { groups: [group], organization_id: group.organization_id } }
 
       it_behaves_like 'an encrypted routable token for resource', prefix do
         let(:resource) { group }
@@ -1623,7 +1613,7 @@ def expect_db_update
 
     shared_examples 'a project runner encrypted token' do |prefix|
       let(:runner_type) { :project_type }
-      let(:attrs) { { projects: [project], sharding_key_id: project.id } }
+      let(:attrs) { { projects: [project], organization_id: project.organization_id } }
 
       it_behaves_like 'an encrypted routable token for resource', prefix do
         let(:resource) { project }
@@ -1865,6 +1855,30 @@ def expect_db_update
           .to change { runner.runner_managers.with_system_xid(system_xid).pluck(:organization_id) }
             .from([]).to([runner.organization_id])
       end
+
+      context 'when runner sharding_key_id is not NULL' do
+        before do
+          runner.update!(sharding_key_id: runner.owner.id)
+        end
+
+        it "populates with runner's sharding_key_id" do
+          expect { ensure_manager }
+            .to change { runner.runner_managers.with_system_xid(system_xid).pluck(:sharding_key_id) }
+              .from([]).to([runner.sharding_key_id])
+        end
+      end
+
+      context 'when runner sharding_key_id is NULL' do
+        before do
+          runner.update!(sharding_key_id: nil)
+        end
+
+        it 'populates a bogus sharding_key_id' do
+          expect { ensure_manager }
+            .to change { runner.runner_managers.with_system_xid(system_xid).pluck(:sharding_key_id) }
+              .from([]).to([0])
+        end
+      end
     end
 
     context 'with group runner' do
@@ -2573,44 +2587,5 @@ def expect_db_update
         it { is_expected.to contain_exactly(instance_runner, group_runner, project_runner) }
       end
     end
-
-    describe '.with_sharding_key' do
-      subject(:scope) { described_class.with_runner_type(runner_type).with_sharding_key(sharding_key_id) }
-
-      let_it_be(:group_runner) { create(:ci_runner, :group, groups: [group]) }
-      let_it_be(:project_runner) { create(:ci_runner, :project, projects: [project, other_project]) }
-
-      context 'with group_type' do
-        let(:runner_type) { 'group_type' }
-
-        context 'when sharding_key_id exists' do
-          let(:sharding_key_id) { group.id }
-
-          it { is_expected.to contain_exactly(group_runner) }
-        end
-
-        context 'when sharding_key_id does not exist' do
-          let(:sharding_key_id) { non_existing_record_id }
-
-          it { is_expected.to eq [] }
-        end
-      end
-
-      context 'with project_type' do
-        let(:runner_type) { 'project_type' }
-
-        context 'when sharding_key_id exists' do
-          let(:sharding_key_id) { project.id }
-
-          it { is_expected.to contain_exactly(project_runner) }
-        end
-
-        context 'when sharding_key_id does not exist' do
-          let(:sharding_key_id) { non_existing_record_id }
-
-          it { is_expected.to eq [] }
-        end
-      end
-    end
   end
 end
diff --git a/spec/models/ci/runner_tagging_spec.rb b/spec/models/ci/runner_tagging_spec.rb
index e21331b476d9da47a529bf104be8af76653a541a..1e1e7ef7c50951f02b1ebdf3bb8df16baaf4f5ea 100644
--- a/spec/models/ci/runner_tagging_spec.rb
+++ b/spec/models/ci/runner_tagging_spec.rb
@@ -10,41 +10,8 @@
 
   describe 'validations' do
     it { is_expected.to validate_presence_of(:runner_type) }
-    it { is_expected.to validate_presence_of(:sharding_key_id) }
     it { is_expected.to validate_presence_of(:organization_id).on([:create, :update]) }
 
-    describe 'sharding_key_id' do
-      subject(:runner_tagging) { runner.taggings.first }
-
-      context 'when runner_type is instance_type' do
-        let(:runner) { create(:ci_runner, :instance, tag_list: ['postgres']) }
-
-        it { is_expected.to be_valid }
-
-        context 'and sharding_key_id is not nil' do
-          before do
-            runner_tagging.sharding_key_id = group.id
-          end
-
-          it { is_expected.to be_invalid }
-        end
-      end
-
-      context 'when runner_type is group_type' do
-        let(:runner) { create(:ci_runner, :group, groups: [group], tag_list: ['postgres']) }
-
-        it { is_expected.to be_valid }
-
-        context 'and sharding_key_id is nil' do
-          before do
-            runner_tagging.sharding_key_id = nil
-          end
-
-          it { is_expected.to be_invalid }
-        end
-      end
-    end
-
     describe 'organization_id' do
       subject(:runner_tagging) { runner.taggings.first }
 
diff --git a/spec/services/ci/runners/update_project_runners_owner_service_spec.rb b/spec/services/ci/runners/update_project_runners_owner_service_spec.rb
deleted file mode 100644
index c0ef5e1a716376b85963f59136e1c959299ce6d6..0000000000000000000000000000000000000000
--- a/spec/services/ci/runners/update_project_runners_owner_service_spec.rb
+++ /dev/null
@@ -1,74 +0,0 @@
-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe ::Ci::Runners::UpdateProjectRunnersOwnerService, '#execute', feature_category: :runner do
-  let_it_be(:owner_group) { create(:group) }
-  let_it_be(:owner_project) { create(:project, group: owner_group) }
-  let_it_be(:new_projects) { create_list(:project, 2) }
-
-  let_it_be(:owned_runner1) do
-    create(:ci_runner, :project, projects: [owner_project, new_projects.first], tag_list: %w[tag1])
-  end
-
-  let_it_be(:owned_runner2) { create(:ci_runner, :project, projects: [owner_project], tag_list: %w[tag1 tag2]) }
-  let_it_be(:owned_runner3) do
-    create(:ci_runner, :project, projects: [owner_project, *new_projects.reverse], tag_list: %w[tag2])
-  end
-
-  let_it_be(:owned_runner4) do
-    create(:ci_runner, :project, projects: [owner_project, *new_projects], tag_list: %w[tag1 tag2])
-  end
-
-  let_it_be(:other_runner) { create(:ci_runner, :project, projects: new_projects, tag_list: %w[tag1 tag2]) }
-  let_it_be(:orphaned_runner) { create(:ci_runner, :project, :without_projects, tag_list: %w[tag1 tag2]) }
-
-  let_it_be(:owned_runner1_manager) { create(:ci_runner_machine, runner: owned_runner1) }
-  let_it_be(:owned_runner2_manager) { create(:ci_runner_machine, runner: owned_runner2) }
-  let_it_be(:owned_runner3_manager) { create(:ci_runner_machine, runner: owned_runner3) }
-  let_it_be(:owned_runner4_manager) { create(:ci_runner_machine, runner: owned_runner4) }
-
-  let(:service) { described_class.new(owner_project.id, owner_project.namespace_id) }
-
-  subject(:execute) { service.execute }
-
-  before_all do
-    owner_project.destroy!
-  end
-
-  before do
-    stub_const("#{described_class}::BATCH_SIZE", 2)
-  end
-
-  it 'updates sharding_key_id on affected runners', :aggregate_failures do
-    expect { execute }
-      # owned_runner1's owner project was deleted
-      .to change { owned_runner1.reload.sharding_key_id }.from(owner_project.id).to(new_projects.first.id)
-      .and change { owned_runner1_manager.reload.sharding_key_id }.from(owner_project.id).to(new_projects.first.id)
-      .and change { tagging_sharding_key_id_for_runner(owned_runner1) }.from(owner_project.id).to(new_projects.first.id)
-      # owned_runner2's owner project was deleted and there were no other associated projects to fall back to
-      .and change { Ci::Runner.find_by_id(owned_runner2) }.to(nil) # delete, since no other project to adopt it
-      .and change { Ci::RunnerManager.find_by_id(owned_runner2_manager) }.to(nil)
-      .and change { Ci::RunnerTagging.find_by_runner_id(owned_runner2) }.to(nil)
-      # owned_runner3's owner project was deleted
-      .and change { owned_runner3.reload.sharding_key_id }.from(owner_project.id).to(new_projects.last.id)
-      .and change { owned_runner3_manager.reload.sharding_key_id }.from(owner_project.id).to(new_projects.last.id)
-      .and change { tagging_sharding_key_id_for_runner(owned_runner3) }.from(owner_project.id).to(new_projects.last.id)
-      # owned_runner4's owner project was deleted
-      .and change { owned_runner4.reload.sharding_key_id }.from(owner_project.id).to(new_projects.first.id)
-      .and change { owned_runner4_manager.reload.sharding_key_id }.from(owner_project.id).to(new_projects.first.id)
-      .and change { tagging_sharding_key_id_for_runner(owned_runner4) }.from(owner_project.id).to(new_projects.first.id)
-      # runners whose owner project was not affected
-      .and not_change { other_runner.reload.sharding_key_id }.from(new_projects.first.id)
-      .and not_change { orphaned_runner.reload.sharding_key_id }
-      .and not_change { tagging_sharding_key_id_for_runner(orphaned_runner) }
-
-    expect(execute).to be_success
-  end
-
-  private
-
-  def tagging_sharding_key_id_for_runner(runner)
-    runner.taggings.pluck(:sharding_key_id).uniq.sole
-  end
-end
diff --git a/spec/workers/ci/runners/update_project_runners_owner_worker_spec.rb b/spec/workers/ci/runners/update_project_runners_owner_worker_spec.rb
deleted file mode 100644
index ab5cbdbc6f02797fce6c2711ab6d972856d6f848..0000000000000000000000000000000000000000
--- a/spec/workers/ci/runners/update_project_runners_owner_worker_spec.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe Ci::Runners::UpdateProjectRunnersOwnerWorker, '#handle_event', feature_category: :runner do
-  let_it_be(:project) { create(:project).tap(&:destroy) }
-
-  let(:project_deleted_event) { Projects::ProjectDeletedEvent.new(data: data) }
-  let(:data) do
-    { project_id: project.id, namespace_id: project.namespace_id, root_namespace_id: project.root_namespace.id }
-  end
-
-  it_behaves_like 'subscribes to event' do
-    let(:event) { project_deleted_event }
-  end
-
-  it 'calls Ci::Runners::UpdateProjectRunnersOwnerService' do
-    expect_next_instance_of(
-      Ci::Runners::UpdateProjectRunnersOwnerService, project.id, project.namespace_id
-    ) do |service|
-      expect(service).to receive(:execute)
-    end
-
-    described_class.new.handle_event(project_deleted_event)
-  end
-end