diff --git a/core/lib/Drupal/Core/Extension/ModuleInstaller.php b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
index 412a7b3..afba2ff 100644
--- a/core/lib/Drupal/Core/Extension/ModuleInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
@@ -295,7 +295,7 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
 
     // If any modules were newly installed, invoke hook_modules_installed().
     if (!empty($modules_installed)) {
-      \Drupal::service('router.builder')->rebuild();
+      \Drupal::service('router.builder')->setRebuildNeeded();
       $this->moduleHandler->invokeAll('modules_installed', array($modules_installed));
     }
 
@@ -437,7 +437,7 @@ public function uninstall(array $module_list, $uninstall_dependents = TRUE) {
       $schema_store = \Drupal::keyValue('system.schema');
       $schema_store->delete($module);
     }
-    \Drupal::service('router.builder')->rebuild();
+    \Drupal::service('router.builder')->setRebuildNeeded();
     drupal_get_installed_schema_version(NULL, TRUE);
 
     // Let other modules react.
diff --git a/core/lib/Drupal/Core/Routing/RouteBuilder.php b/core/lib/Drupal/Core/Routing/RouteBuilder.php
index db516af..c3f494a 100644
--- a/core/lib/Drupal/Core/Routing/RouteBuilder.php
+++ b/core/lib/Drupal/Core/Routing/RouteBuilder.php
@@ -45,13 +45,6 @@ class RouteBuilder implements RouteBuilderInterface, DestructableInterface {
   protected $dispatcher;
 
   /**
-   * The yaml discovery used to find all the .routing.yml files.
-   *
-   * @var \Drupal\Component\Discovery\YamlDiscovery
-   */
-  protected $yamlDiscovery;
-
-  /**
    * The module handler.
    *
    * @var \Drupal\Core\Extension\ModuleHandlerInterface
@@ -232,10 +225,8 @@ public function destruct() {
    *   The defined routes, keyed by provider.
    */
   protected function getRouteDefinitions() {
-    if (!isset($this->yamlDiscovery)) {
-      $this->yamlDiscovery = new YamlDiscovery('routing', $this->moduleHandler->getModuleDirectories());
-    }
-    return $this->yamlDiscovery->findAll();
+    $discovery = new YamlDiscovery('routing', $this->moduleHandler->getModuleDirectories());
+    return $discovery->findAll();
   }
 
 }
diff --git a/core/modules/book/src/Tests/BookUninstallTest.php b/core/modules/book/src/Tests/BookUninstallTest.php
index dbd4de5..5762366 100644
--- a/core/modules/book/src/Tests/BookUninstallTest.php
+++ b/core/modules/book/src/Tests/BookUninstallTest.php
@@ -23,14 +23,13 @@ class BookUninstallTest extends KernelTestBase {
    *
    * @var array
    */
-  public static $modules = array('system', 'user', 'field', 'filter', 'text', 'entity_reference', 'node', 'book');
+  public static $modules = array('user', 'field', 'filter', 'text', 'entity_reference', 'node', 'book');
 
   /**
    * {@inheritdoc}
    */
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', array('router'));
     $this->installEntitySchema('user');
     $this->installEntitySchema('node');
     $this->installSchema('book', array('book'));
diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index ab303b6..25558d3 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -44,7 +44,6 @@ protected function setUp() {
 
     // Install the Filter module.
     $this->installSchema('system', 'url_alias');
-    $this->installSchema('system', 'router');
 
     // Create text format, associate CKEditor.
     $filtered_html_format = entity_create('filter_format', array(
diff --git a/core/modules/comment/src/Tests/CommentStringIdEntitiesTest.php b/core/modules/comment/src/Tests/CommentStringIdEntitiesTest.php
index ddfaf8f..3cb8ab0 100644
--- a/core/modules/comment/src/Tests/CommentStringIdEntitiesTest.php
+++ b/core/modules/comment/src/Tests/CommentStringIdEntitiesTest.php
@@ -29,7 +29,6 @@ class CommentStringIdEntitiesTest extends KernelTestBase {
     'field_ui',
     'entity',
     'entity_test',
-    'system',
     'text',
   );
 
@@ -37,7 +36,6 @@ protected function setUp() {
     parent::setUp();
     $this->installEntitySchema('comment');
     $this->installSchema('comment', array('comment_entity_statistics'));
-    $this->installSchema('system', array('router'));
     // Create the comment body field storage.
     $this->installConfig(array('field'));
   }
diff --git a/core/modules/config/src/Tests/ConfigCRUDTest.php b/core/modules/config/src/Tests/ConfigCRUDTest.php
index c530b96..f42d722 100644
--- a/core/modules/config/src/Tests/ConfigCRUDTest.php
+++ b/core/modules/config/src/Tests/ConfigCRUDTest.php
@@ -39,11 +39,6 @@ class ConfigCRUDTest extends KernelTestBase {
    */
   public static $modules = array('system');
 
-  protected function setUp() {
-      parent::setUp();
-      $this->installSchema('system', 'router');
-    }
-
   /**
    * Tests CRUD operations.
    */
diff --git a/core/modules/config/src/Tests/DefaultConfigTest.php b/core/modules/config/src/Tests/DefaultConfigTest.php
index 2d5412c..99ff07a 100644
--- a/core/modules/config/src/Tests/DefaultConfigTest.php
+++ b/core/modules/config/src/Tests/DefaultConfigTest.php
@@ -45,7 +45,6 @@ class DefaultConfigTest extends KernelTestBase {
 
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', 'router');
     \Drupal::service('theme_handler')->install($this->themes);
   }
 
diff --git a/core/modules/field_ui/src/Tests/EntityDisplayTest.php b/core/modules/field_ui/src/Tests/EntityDisplayTest.php
index 9cedc2d..ef0f476 100644
--- a/core/modules/field_ui/src/Tests/EntityDisplayTest.php
+++ b/core/modules/field_ui/src/Tests/EntityDisplayTest.php
@@ -26,7 +26,6 @@ class EntityDisplayTest extends KernelTestBase {
 
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', array('router'));
     $this->installEntitySchema('node');
     $this->installConfig(array('field'));
   }
diff --git a/core/modules/filter/src/Tests/FilterAPITest.php b/core/modules/filter/src/Tests/FilterAPITest.php
index 3ceb5eb..6ee11e2 100644
--- a/core/modules/filter/src/Tests/FilterAPITest.php
+++ b/core/modules/filter/src/Tests/FilterAPITest.php
@@ -28,7 +28,6 @@ class FilterAPITest extends EntityUnitTestBase {
   protected function setUp() {
     parent::setUp();
 
-    $this->installSchema('system', array('router'));
     $this->installConfig(array('system', 'filter'));
   }
 
diff --git a/core/modules/node/src/Tests/Config/NodeImportCreateTest.php b/core/modules/node/src/Tests/Config/NodeImportCreateTest.php
index f6902e39..97fe51f 100644
--- a/core/modules/node/src/Tests/Config/NodeImportCreateTest.php
+++ b/core/modules/node/src/Tests/Config/NodeImportCreateTest.php
@@ -30,7 +30,6 @@ class NodeImportCreateTest extends KernelTestBase {
    */
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', array('router'));
     $this->installEntitySchema('user');
 
     // Set default storage backend.
diff --git a/core/modules/simpletest/src/Tests/KernelTestBaseTest.php b/core/modules/simpletest/src/Tests/KernelTestBaseTest.php
index 8d2382e..218d0b9 100644
--- a/core/modules/simpletest/src/Tests/KernelTestBaseTest.php
+++ b/core/modules/simpletest/src/Tests/KernelTestBaseTest.php
@@ -21,7 +21,7 @@ class KernelTestBaseTest extends KernelTestBase {
    *
    * @var array
    */
-  public static $modules = array('entity_test', 'system');
+  public static $modules = array('entity_test');
 
   /**
    * {@inheritdoc}
@@ -44,7 +44,6 @@ function simpletest_test_stub_settings_function() {}
 
     $original_container = $this->originalContainer;
     parent::setUp();
-    $this->installSchema('system', array('router'));
     $this->assertNotIdentical(\Drupal::getContainer(), $original_container, 'KernelTestBase test creates a new container.');
   }
 
@@ -52,7 +51,7 @@ function simpletest_test_stub_settings_function() {}
    * Tests expected behavior of setUp().
    */
   function testSetUp() {
-    $modules = array('entity_test', 'system');
+    $modules = array('entity_test');
     $table = 'entity_test';
 
     // Verify that specified $modules have been loaded.
diff --git a/core/modules/system/src/Tests/Field/FieldModuleUninstallValidatorTest.php b/core/modules/system/src/Tests/Field/FieldModuleUninstallValidatorTest.php
index ea46747..f427ade 100644
--- a/core/modules/system/src/Tests/Field/FieldModuleUninstallValidatorTest.php
+++ b/core/modules/system/src/Tests/Field/FieldModuleUninstallValidatorTest.php
@@ -31,7 +31,6 @@ class FieldModuleUninstallValidatorTest extends EntityUnitTestBase {
    */
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', 'router');
     $this->installSchema('user', 'users_data');
     $this->entityDefinitionUpdateManager = $this->container->get('entity.definition_update_manager');
 
diff --git a/core/modules/system/src/Tests/Module/ModuleImplementsAlterTest.php b/core/modules/system/src/Tests/Module/ModuleImplementsAlterTest.php
index b831830..2a34c20 100644
--- a/core/modules/system/src/Tests/Module/ModuleImplementsAlterTest.php
+++ b/core/modules/system/src/Tests/Module/ModuleImplementsAlterTest.php
@@ -16,16 +16,6 @@
  */
 class ModuleImplementsAlterTest extends KernelTestBase {
 
-  public static $modules = array('system');
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-    $this->installSchema('system', array('router'));
-  }
-
   /**
    * Tests hook_module_implements_alter() adding an implementation.
    *
diff --git a/core/modules/system/src/Tests/Routing/RouterTest.php b/core/modules/system/src/Tests/Routing/RouterTest.php
index 85e5e4b..92e9608 100644
--- a/core/modules/system/src/Tests/Routing/RouterTest.php
+++ b/core/modules/system/src/Tests/Routing/RouterTest.php
@@ -194,6 +194,7 @@ public function testControllerResolutionAjax() {
    */
   public function testRouterUninstallInstall() {
     \Drupal::service('module_installer')->uninstall(array('router_test'));
+    \Drupal::service('router.builder')->rebuild();
     try {
       \Drupal::service('router.route_provider')->getRouteByName('router_test.1');
       $this->fail('Route was delete on uninstall.');
@@ -203,6 +204,7 @@ public function testRouterUninstallInstall() {
     }
     // Install the module again.
     \Drupal::service('module_installer')->install(array('router_test'));
+    \Drupal::service('router.builder')->rebuild();
     $route = \Drupal::service('router.route_provider')->getRouteByName('router_test.1');
     $this->assertNotNull($route, 'Route exists after module installation');
   }
diff --git a/core/modules/system/src/Tests/System/InfoAlterTest.php b/core/modules/system/src/Tests/System/InfoAlterTest.php
index 42f5041..02cdd17 100644
--- a/core/modules/system/src/Tests/System/InfoAlterTest.php
+++ b/core/modules/system/src/Tests/System/InfoAlterTest.php
@@ -19,14 +19,6 @@ class InfoAlterTest extends KernelTestBase {
   public static $modules = array('system');
 
   /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-    $this->installSchema('system', array('router'));
-  }
-
-  /**
    * Tests that theme .info.yml data is rebuild after enabling a module.
    *
    * Tests that info data is rebuilt after a module that implements
diff --git a/core/modules/system/src/Tests/System/TrustedHostsTest.php b/core/modules/system/src/Tests/System/TrustedHostsTest.php
index 3719bd1..e54decc 100644
--- a/core/modules/system/src/Tests/System/TrustedHostsTest.php
+++ b/core/modules/system/src/Tests/System/TrustedHostsTest.php
@@ -69,6 +69,7 @@ public function testStatusPageWithConfiguration() {
    */
   public function testFakeRequests() {
     $this->container->get('module_installer')->install(['trusted_hosts_test']);
+    $this->container->get('router.builder')->rebuild();
 
     $host = $this->container->get('request_stack')->getCurrentRequest()->getHost();
     $settings['settings']['trusted_host_patterns'] = (object) array(
@@ -88,6 +89,7 @@ public function testFakeRequests() {
   public function testShortcut() {
     $this->container->get('module_installer')->install(['block', 'shortcut']);
     $this->rebuildContainer();
+    $this->container->get('router.builder')->rebuild();
 
     /** @var \Drupal\Core\Entity\EntityManagerInterface $entity_manager */
     $entity_manager = $this->container->get('entity.manager');
diff --git a/core/modules/system/src/Tests/Theme/RegistryTest.php b/core/modules/system/src/Tests/Theme/RegistryTest.php
index 763372e..8872f10 100644
--- a/core/modules/system/src/Tests/Theme/RegistryTest.php
+++ b/core/modules/system/src/Tests/Theme/RegistryTest.php
@@ -28,15 +28,6 @@ class RegistryTest extends KernelTestBase {
   protected $profile = 'testing';
 
   /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-     parent::setUp();
-
-     $this->installSchema('system', ['router']);
-  }
-
-  /**
    * Tests the behavior of the theme registry class.
    */
   function testRaceCondition() {
diff --git a/core/modules/system/src/Tests/Theme/ThemeSettingsTest.php b/core/modules/system/src/Tests/Theme/ThemeSettingsTest.php
index 09d73e7..3ef48d0 100644
--- a/core/modules/system/src/Tests/Theme/ThemeSettingsTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeSettingsTest.php
@@ -34,7 +34,6 @@ class ThemeSettingsTest extends KernelTestBase {
 
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', array('router'));
     // Theme settings rely on System module's system.theme.global configuration.
     $this->installConfig(array('system'));
 
diff --git a/core/modules/tracker/src/Tests/TrackerTest.php b/core/modules/tracker/src/Tests/TrackerTest.php
index 3ca1dc4..94e981d 100644
--- a/core/modules/tracker/src/Tests/TrackerTest.php
+++ b/core/modules/tracker/src/Tests/TrackerTest.php
@@ -347,6 +347,7 @@ function testTrackerCronIndexing() {
    */
   function testTrackerAdminUnpublish() {
     \Drupal::service('module_installer')->install(array('views'));
+    \Drupal::service('router.builder')->rebuild();
     $admin_user = $this->drupalCreateUser(array('access content overview', 'administer nodes', 'bypass node access'));
     $this->drupalLogin($admin_user);
 
diff --git a/core/modules/user/src/Tests/UserCancelTest.php b/core/modules/user/src/Tests/UserCancelTest.php
index 029a66c..2ef966a 100644
--- a/core/modules/user/src/Tests/UserCancelTest.php
+++ b/core/modules/user/src/Tests/UserCancelTest.php
@@ -72,6 +72,7 @@ function testUserCancelWithoutPermission() {
    */
   public function testUserCancelChangePermission() {
     \Drupal::service('module_installer')->install(array('user_form_test'));
+    \Drupal::service('router.builder')->rebuild();
     $this->config('user.settings')->set('cancel_method', 'user_cancel_reassign')->save();
 
     // Create a regular user.
@@ -96,6 +97,7 @@ public function testUserCancelChangePermission() {
    */
   function testUserCancelUid1() {
     \Drupal::service('module_installer')->install(array('views'));
+    \Drupal::service('router.builder')->rebuild();
     // Update uid 1's name and password to we know it.
     $password = user_password();
     $account = array(
@@ -453,6 +455,7 @@ function testUserWithoutEmailCancelByAdmin() {
    */
   function testMassUserCancelByAdmin() {
     \Drupal::service('module_installer')->install(array('views'));
+    \Drupal::service('router.builder')->rebuild();
     $this->config('user.settings')->set('cancel_method', 'user_cancel_reassign')->save();
     // Enable account cancellation notification.
     $this->config('user.settings')->set('notify.status_canceled', TRUE)->save();
diff --git a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
index b8f212f..36cd9cd 100644
--- a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
@@ -290,6 +290,13 @@ public function setYamlDiscovery(YamlDiscovery $yaml_discovery) {
     $this->yamlDiscovery = $yaml_discovery;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function getRouteDefinitions() {
+    return $this->yamlDiscovery->findAll();
+  }
+
 }
 
 /**