diff --git a/config/schema/search_api.index.schema.yml b/config/schema/search_api.index.schema.yml
index 427f03f..bec9eb0 100644
--- a/config/schema/search_api.index.schema.yml
+++ b/config/schema/search_api.index.schema.yml
@@ -17,7 +17,7 @@ search_api.index.*:
     read_only:
       type: boolean
       label: 'Read-only'
-    fields:
+    field_settings:
       type: sequence
       label: 'Indexed fields'
       sequence:
@@ -76,23 +76,30 @@ search_api.index.*:
         index_directly:
           type: boolean
           label: 'Index items immediately'
-    datasources:
+    datasource_settings:
       type: sequence
-      label: 'Datasource plugin IDs'
+      label: 'Datasource settings'
       sequence:
-        type: string
-    datasource_configs:
+        type: mapping
+        label: 'A datasource'
+        mapping:
+          plugin_id:
+            type: string
+            label: 'The plugin ID of the datasource config'
+          settings:
+            type: plugin.plugin_configuration.search_api_datasource.[%parent.plugin_id]
+    tracker_settings:
       type: sequence
-      label: 'Datasource plugin configurations'
+      label: 'Tracker settings'
       sequence:
-        type: plugin.plugin_configuration.search_api_datasource.[%key]
-        label: 'Datasource plugin configuration'
-    tracker:
-      type: string
-      label: 'Tracker plugin ID'
-    tracker_config:
-      label: 'Tracker config plugin'
-      type: plugin.plugin_configuration.search_api_tracker.[%parent.tracker]
+        type: mapping
+        label: 'A tracker'
+        mapping:
+          plugin_id:
+            type: string
+            label: 'The plugin ID of the tracker config'
+          settings:
+            type: plugin.plugin_configuration.search_api_tracker.[%parent.plugin_id]
     server:
       type: string
       label: 'Server ID'
diff --git a/config/schema/search_api.tracker.schema.yml b/config/schema/search_api.tracker.schema.yml
index 297badc..1cb3518 100644
--- a/config/schema/search_api.tracker.schema.yml
+++ b/config/schema/search_api.tracker.schema.yml
@@ -1,4 +1,3 @@
-# @todo Update the key when https://www.drupal.org/node/2291073 is fixed.
 plugin.plugin_configuration.search_api_tracker.default:
   type: sequence
   label: 'Entity tracker configuration'
diff --git a/search_api.drush.inc b/search_api.drush.inc
index e403668..07954f8 100644
--- a/search_api.drush.inc
+++ b/search_api.drush.inc
@@ -325,8 +325,8 @@ function drush_search_api_status($index_id = NULL) {
   );
 
   foreach ($indexes as $index) {
-    $indexed = $index->getTracker()->getIndexedItemsCount();
-    $total = $index->getTracker()->getTotalItemsCount();
+    $indexed = $index->getTrackerInstance()->getIndexedItemsCount();
+    $total = $index->getTrackerInstance()->getTotalItemsCount();
 
     $complete = '-';
     if ($total > 0) {
@@ -365,7 +365,7 @@ function drush_search_api_index($index_id = NULL, $limit = NULL, $batch_size = N
   }
 
   foreach ($indexes as $index) {
-    $tracker = $index->getTracker();
+    $tracker = $index->getTrackerInstance();
     $remaining = $tracker->getTotalItemsCount() - $tracker->getIndexedItemsCount();
 
     if (!$remaining) {
diff --git a/search_api.theme.inc b/search_api.theme.inc
index 7de7c73..677cf52 100644
--- a/search_api.theme.inc
+++ b/search_api.theme.inc
@@ -230,7 +230,7 @@ function theme_search_api_index($variables) {
   /** @var $index \Drupal\search_api\IndexInterface */
   $index = $variables['index'];
   $server = $index->hasValidServer() ? $index->getServer() : NULL;
-  $tracker = $index->hasValidTracker() ? $index->getTracker() : NULL;
+  $tracker = $index->hasValidTracker() ? $index->getTrackerInstance() : NULL;
 
   $output = '';
 
diff --git a/search_api_db/search_api_db_defaults/config/optional/search_api.index.default_index.yml b/search_api_db/search_api_db_defaults/config/optional/search_api.index.default_index.yml
index 7941caa..4587ca0 100644
--- a/search_api_db/search_api_db_defaults/config/optional/search_api.index.default_index.yml
+++ b/search_api_db/search_api_db_defaults/config/optional/search_api.index.default_index.yml
@@ -2,7 +2,7 @@ id: default_index
 name: 'Default content index'
 description: 'Default content index created by the Database Search Defaults module'
 read_only: false
-fields:
+field_settings:
   search_api_language:
     label: 'Item language'
     type: string
@@ -202,16 +202,18 @@ processors:
 options:
   index_directly: true
   cron_limit: 50
-datasources:
-  - 'entity:node'
-datasource_configs:
+datasource_settings:
   'entity:node':
-    default: '1'
-    bundles:
-      article: '0'
-      page: '0'
-tracker: default
-tracker_config: {  }
+    plugin_id: 'entity:node'
+    settings:
+      default: '1'
+      bundles:
+        article: '0'
+        page: '0'
+tracker_settings:
+  'default':
+    plugin_id: default
+    settings: {  }
 server: default_server
 status: true
 langcode: en
diff --git a/search_api_db/tests/src/Kernel/BackendTest.php b/search_api_db/tests/src/Kernel/BackendTest.php
index 5c43111..62b4bee 100644
--- a/search_api_db/tests/src/Kernel/BackendTest.php
+++ b/search_api_db/tests/src/Kernel/BackendTest.php
@@ -157,8 +157,11 @@ class BackendTest extends KernelTestBase {
     $index = $this->getIndex();
     $this->assertTrue((bool) $index, 'The index was successfully created.');
 
-    $this->assertEquals(5, $index->getTracker()->getTotalItemsCount(), 'Correct item count.');
-    $this->assertEquals(0, $index->getTracker()->getIndexedItemsCount(), 'All items still need to be indexed.');
+    $this->assertEquals(array("entity:entity_test"), $index->getDatasourceIds());
+    $this->assertEquals('default', $index->getTrackerId());
+
+    $this->assertEquals(5, $index->getTrackerInstance()->getTotalItemsCount(), 'Correct item count.');
+    $this->assertEquals(0, $index->getTrackerInstance()->getIndexedItemsCount(), 'All items still need to be indexed.');
   }
 
   /**
diff --git a/src/Entity/Index.php b/src/Entity/Index.php
index c466fc1..59a9f21 100644
--- a/src/Entity/Index.php
+++ b/src/Entity/Index.php
@@ -57,13 +57,11 @@ use Drupal\views\Views;
  *     "name",
  *     "description",
  *     "read_only",
- *     "fields",
+ *     "field_settings",
  *     "processors",
  *     "options",
- *     "datasources",
- *     "datasource_configs",
- *     "tracker",
- *     "tracker_config",
+ *     "datasource_settings",
+ *     "tracker_settings",
  *     "server",
  *   },
  *   links = {
@@ -115,7 +113,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *
    * @var array
    */
-  protected $fields = array();
+  protected $field_settings = array();
 
   /**
    * An array of options configuring this index.
@@ -127,18 +125,11 @@ class Index extends ConfigEntityBase implements IndexInterface {
   protected $options = array();
 
   /**
-   * The IDs of the datasources selected for this index.
+   * The settings of the datasources selected for this index.
    *
    * @var string[]
    */
-  protected $datasources = array();
-
-  /**
-   * The configuration for the selected datasources.
-   *
-   * @var array
-   */
-  protected $datasource_configs = array();
+  protected $datasource_settings = array();
 
   /**
    * The instantiated datasource plugins.
@@ -147,30 +138,28 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *
    * @see getDatasources()
    */
-  protected $datasourcePlugins;
-
-  /**
-   * The tracker plugin ID.
-   *
-   * @var string
-   */
-  protected $tracker = 'default';
+  protected $datasourceInstances;
 
   /**
-   * The tracker plugin configuration.
+   * The tracker settings
    *
    * @var array
    */
-  protected $tracker_config = array();
+  protected $tracker_settings = array(
+    'default' => array(
+      'plugin_id' => 'default',
+      'settings' => array()
+    ),
+  );
 
   /**
    * The tracker plugin instance.
    *
    * @var \Drupal\search_api\Tracker\TrackerInterface|null
    *
-   * @see getTracker()
+   * @see getTrackerInstance()
    */
-  protected $trackerPlugin;
+  protected $trackerInstance;
 
   /**
    * The ID of the server on which data should be indexed.
@@ -210,7 +199,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *
    * @see loadProcessors()
    */
-  protected $processorPlugins;
+  protected $processorInstances;
 
   /**
    * Whether reindexing has been triggered for this index in this page request.
@@ -301,7 +290,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getDatasourceIds() {
-    return $this->datasources;
+    return array_keys($this->datasource_settings);
   }
 
   /**
@@ -329,20 +318,20 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getDatasources($only_enabled = TRUE) {
-    if (!isset($this->datasourcePlugins)) {
-      $this->datasourcePlugins = array();
+    if (!isset($this->datasourceInstances)) {
+      $this->datasourceInstances = array();
       /** @var $datasource_plugin_manager \Drupal\search_api\Datasource\DatasourcePluginManager */
       $datasource_plugin_manager = \Drupal::service('plugin.manager.search_api.datasource');
 
       foreach ($datasource_plugin_manager->getDefinitions() as $name => $datasource_definition) {
-        if (class_exists($datasource_definition['class']) && empty($this->datasourcePlugins[$name])) {
+        if (class_exists($datasource_definition['class']) && empty($this->datasourceInstances[$name])) {
           // Create our settings for this datasource.
-          $config = isset($this->datasource_configs[$name]) ? $this->datasource_configs[$name] : array();
+          $config = isset($this->datasource_settings[$name]) ? $this->datasource_settings[$name]['settings'] : array();
           $config += array('index' => $this);
 
           /** @var $datasource \Drupal\search_api\Datasource\DatasourceInterface */
           $datasource = $datasource_plugin_manager->createInstance($name, $config);
-          $this->datasourcePlugins[$name] = $datasource;
+          $this->datasourceInstances[$name] = $datasource;
         }
         elseif (!class_exists($datasource_definition['class'])) {
           \Drupal::logger('search_api')->warning('Datasource @id specifies a non-existing @class.', array('@id' => $name, '@class' => $datasource_definition['class']));
@@ -352,9 +341,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
 
     // Filter datasources by status if required.
     if (!$only_enabled) {
-      return $this->datasourcePlugins;
+      return $this->datasourceInstances;
     }
-    return array_intersect_key($this->datasourcePlugins, array_flip($this->datasources));
+
+    return array_intersect_key($this->datasourceInstances, array_flip(array_keys($this->datasource_settings)));
   }
 
   /**
@@ -368,23 +358,35 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getTrackerId() {
-    return $this->tracker;
+    if (is_null($this->tracker_settings)) {
+      return 'default';
+    }
+
+    $plugins = array_keys($this->tracker_settings);
+    return $this->tracker_settings[$plugins[0]]['plugin_id'];
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getTracker() {
-    if (!$this->trackerPlugin) {
-      $tracker_plugin_configuration = array('index' => $this) + $this->tracker_config;
-      if (!($this->trackerPlugin = \Drupal::service('plugin.manager.search_api.tracker')->createInstance($this->getTrackerId(), $tracker_plugin_configuration))) {
-        $args['@tracker'] = $this->tracker;
+  public function getTrackerInstance() {
+    if (!$this->trackerInstance) {
+
+      if (is_null($this->tracker_settings)) {
+        $tracker_plugin_configuration = array('index' => $this);
+      } else {
+        $plugins = array_keys($this->tracker_settings);
+        $tracker_plugin_configuration = array('index' => $this) + $this->tracker_settings[$plugins[0]]['settings'];
+      }
+
+      if (!($this->trackerInstance = \Drupal::service('plugin.manager.search_api.tracker')->createInstance($this->getTrackerId(), $tracker_plugin_configuration))) {
+        $args['@tracker'] = $this->getTrackerId();
         $args['%index'] = $this->label();
         throw new SearchApiException(new FormattableMarkup('The tracker with ID "@tracker" could not be retrieved for index %index.', $args));
       }
     }
 
-    return $this->trackerPlugin;
+    return $this->trackerInstance;
   }
 
   /**
@@ -486,13 +488,13 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *   The loaded processors, keyed by processor ID.
    */
   protected function loadProcessors() {
-    if (empty($this->processorPlugins)) {
+    if (empty($this->processorInstances)) {
       /** @var $processor_plugin_manager \Drupal\search_api\Processor\ProcessorPluginManager */
       $processor_plugin_manager = \Drupal::service('plugin.manager.search_api.processor');
       $processor_settings = $this->getProcessorSettings();
 
       foreach ($processor_plugin_manager->getDefinitions() as $name => $processor_definition) {
-        if (class_exists($processor_definition['class']) && empty($this->processorPlugins[$name])) {
+        if (class_exists($processor_definition['class']) && empty($this->processorInstances[$name])) {
           // Create our settings for this processor.
           $settings = empty($processor_settings[$name]['settings']) ? array() : $processor_settings[$name]['settings'];
           $settings['index'] = $this;
@@ -500,7 +502,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
           /** @var $processor \Drupal\search_api\Processor\ProcessorInterface */
           $processor = $processor_plugin_manager->createInstance($name, $settings);
           if ($processor->supportsIndex($this)) {
-            $this->processorPlugins[$name] = $processor;
+            $this->processorInstances[$name] = $processor;
           }
         }
         elseif (!class_exists($processor_definition['class'])) {
@@ -509,7 +511,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       }
     }
 
-    return $this->processorPlugins;
+    return $this->processorInstances;
   }
 
   /**
@@ -578,7 +580,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       throw new SearchApiException(new FormattableMarkup('Cannot add field with machine name %field_id: machine name is already taken.', $args));
     }
 
-    $this->fields[$field_id] = $field->getSettings();
+    $this->field_settings[$field_id] = $field->getSettings();
 
     $this->resetCaches();
     return $this;
@@ -588,7 +590,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function renameField($old_field_id, $new_field_id) {
-    if (isset($this->fields[$old_field_id])) {
+    if (isset($this->getFields()[$old_field_id])) {
       $args['%field_id'] = $old_field_id;
       throw new SearchApiException(new FormattableMarkup('Could not rename field with machine name %field_id: no such field.', $args));
     }
@@ -596,13 +598,13 @@ class Index extends ConfigEntityBase implements IndexInterface {
       $args['%field_id'] = $new_field_id;
       throw new SearchApiException(new FormattableMarkup('%field_id is a reserved value and cannot be used as the machine name of a normal field.', $args));
     }
-    if (isset($this->fields[$new_field_id])) {
+    if (isset($this->getFields()[$new_field_id])) {
       $args['%field_id'] = $new_field_id;
       throw new SearchApiException(new FormattableMarkup('%field_id is a reserved value and cannot be used as the machine name of a normal field.', $args));
     }
 
-    $this->fields[$new_field_id] = $this->fields[$old_field_id];
-    unset($this->fields[$old_field_id]);
+    $this->field_settings[$new_field_id] = $this->field_settings[$old_field_id];
+    unset($this->field_settings[$old_field_id]);
 
     $this->resetCaches();
     return $this;
@@ -621,7 +623,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       throw new SearchApiException(new FormattableMarkup('Cannot remove field with machine name %field_id: field is locked.', $args));
     }
 
-    unset($this->fields[$field_id]);
+    unset($this->field_settings[$field_id]);
 
     $this->resetCaches();
     return $this;
@@ -657,7 +659,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
   public function getFieldsByDatasource($datasource_id) {
     $datasource_fields = $this->getCache(__FUNCTION__);
     if (!$datasource_fields) {
-      $datasource_fields = array_fill_keys($this->datasources, array());
+      $datasource_fields = array_fill_keys(array_keys($this->datasource_settings), array());
       $datasource_fields[NULL] = array();
       foreach ($this->getFields() as $field_id => $field) {
         $datasource_fields[$field->getDatasourceId()][$field_id] = $field;
@@ -689,14 +691,14 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getFieldSettings() {
-    return $this->fields;
+    return $this->field_settings;
   }
 
   /**
    * {@inheritdoc}
    */
   public function setFieldSettings(array $fields = array()) {
-    $this->fields = $fields;
+    $this->field_settings = $fields;
     return $this;
   }
 
@@ -767,7 +769,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    */
   public function indexItems($limit = '-1', $datasource_id = NULL) {
     if ($this->hasValidTracker() && !$this->isReadOnly()) {
-      $tracker = $this->getTracker();
+      $tracker = $this->getTrackerInstance();
       $next_set = $tracker->getRemainingItems($limit, $datasource_id);
       $items = $this->loadItemsMultiple($next_set);
       if ($items) {
@@ -793,7 +795,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
     if (!$this->status) {
       throw new SearchApiException(new FormattableMarkup("Couldn't index values on index %index (index is disabled)", array('%index' => $this->label())));
     }
-    if (empty($this->fields)) {
+    if (empty($this->getFields())) {
       throw new SearchApiException(new FormattableMarkup("Couldn't index values on index %index (no fields selected)", array('%index' => $this->label())));
     }
 
@@ -838,7 +840,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
 
     if ($processed_ids) {
       if ($this->hasValidTracker()) {
-        $this->getTracker()->trackItemsIndexed($processed_ids);
+        $this->getTrackerInstance()->trackItemsIndexed($processed_ids);
       }
       // Since we've indexed items now, triggering reindexing would have some
       // effect again. Therefore, we reset the flag.
@@ -883,7 +885,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       foreach ($ids as $id) {
         $item_ids[] = Utility::createCombinedId($datasource_id, $id);
       }
-      $this->getTracker()->$tracker_method($item_ids);
+      $this->getTrackerInstance()->$tracker_method($item_ids);
       if (!$this->isReadOnly() && $this->getOption('index_directly')) {
         try {
           $items = $this->loadItemsMultiple($item_ids);
@@ -907,7 +909,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       foreach ($ids as $id) {
         $item_ids[] = Utility::createCombinedId($datasource_id, $id);
       }
-      $this->getTracker()->trackItemsDeleted($item_ids);
+      $this->getTrackerInstance()->trackItemsDeleted($item_ids);
       if (!$this->isReadOnly() && $this->isServerEnabled()) {
         $this->getServer()->deleteItems($this, $item_ids);
       }
@@ -920,7 +922,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
   public function reindex() {
     if ($this->status() && !$this->hasReindexed) {
       $this->hasReindexed = TRUE;
-      $this->getTracker()->trackAllItemsUpdated();
+      $this->getTrackerInstance()->trackAllItemsUpdated();
       \Drupal::moduleHandler()->invokeAll('search_api_index_reindex', array($this, FALSE));
     }
   }
@@ -935,7 +937,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       if (!$this->hasReindexed) {
         $invoke_hook = TRUE;
         $this->hasReindexed = TRUE;
-        $this->getTracker()->trackAllItemsUpdated();
+        $this->getTrackerInstance()->trackAllItemsUpdated();
       }
       if (!$this->isReadOnly()) {
         $invoke_hook = TRUE;
@@ -1014,10 +1016,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function resetCaches($include_stored = TRUE) {
-    $this->datasourcePlugins = NULL;
-    $this->trackerPlugin = NULL;
+    $this->datasourceInstances = NULL;
+    $this->trackerInstance = NULL;
     $this->serverInstance = NULL;
-    $this->processorPlugins = NULL;
+    $this->processorInstances = NULL;
     $this->cache = array();
     if ($include_stored) {
       Cache::invalidateTags($this->getCacheTags());
@@ -1069,10 +1071,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
 
     // Remove all "locked" and "hidden" flags from all fields of the index. If
     // they are still valid, they should be re-added by the processors.
-    foreach ($this->fields as $field_id => $field_settings) {
-      unset($this->fields[$field_id]['indexed_locked']);
-      unset($this->fields[$field_id]['type_locked']);
-      unset($this->fields[$field_id]['hidden']);
+    foreach ($this->field_settings as $field_id => $field_settings) {
+      unset($this->field_settings[$field_id]['indexed_locked']);
+      unset($this->field_settings[$field_id]['type_locked']);
+      unset($this->field_settings[$field_id]['hidden']);
     }
 
     // We first have to check for locked processors, otherwise their
@@ -1215,7 +1217,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
    *   The previous version of the index.
    */
   protected function reactToTrackerSwitch(IndexInterface $original) {
-    if ($this->tracker != $original->getTrackerId()) {
+    if ($this->getTrackerId() != $original->getTrackerId()) {
       $index_task_manager = \Drupal::getContainer()->get('search_api.index_task_manager');
       if ($original->hasValidTracker()) {
         $index_task_manager->stopTracking($this);
@@ -1291,7 +1293,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
     /** @var \Drupal\search_api\IndexInterface[] $entities */
     foreach ($entities as $index) {
       if ($index->hasValidTracker()) {
-        $index->getTracker()->trackAllItemsDeleted();
+        $index->getTrackerInstance()->trackAllItemsDeleted();
       }
       if ($index->hasValidServer()) {
         $index->getServer()->removeIndex($index);
@@ -1522,17 +1524,29 @@ class Index extends ConfigEntityBase implements IndexInterface {
     // according to plugin type, unfortunately.
     // First, remove plugins that need to be removed.
     $this->processors = array_intersect_key($this->processors, $all_plugins['processors']);
-    $this->datasources = array_keys($all_plugins['datasources']);
-    $this->datasource_configs = array_intersect_key($this->datasource_configs, $all_plugins['datasources']);
+    $new_datasources = array();
+    foreach ($all_plugins['datasources'] as $plugin_id => $settings) {
+      $new_datasources[$plugin_id] = array(
+        'plugin_id' => $plugin_id,
+        'settings' => $settings,
+      );
+    }
+    $this->datasource_settings = array_intersect_key($this->datasource_settings, $new_datasources);
+
     // There always needs to be a tracker.
     if (empty($all_plugins['tracker'])) {
-      $this->tracker = \Drupal::config('search_api.settings')->get('default_tracker');
-      $this->tracker_config = array();
+      $default_tracker_id = \Drupal::config('search_api.settings')->get('default_tracker');
+      $this->tracker_settings = array(
+        $default_tracker_id = array(
+          'plugin_id' => $default_tracker_id,
+          'settings' => array(),
+        )
+      );
     }
     // There also always needs to be a datasource, but here we have no easy way
     // out – if we had to remove all datasources, the operation fails. Return
     // FALSE to indicate this, which will cause the index to be deleted.
-    if (!$this->datasources) {
+    if (!$this->datasource_settings) {
       return FALSE;
     }
 
@@ -1544,10 +1558,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
             $this->processors[$plugin_id]['settings'] = $plugin_config;
             break;
           case 'datasources':
-            $this->datasource_configs[$plugin_id] = $plugin_config;
+            $this->datasource_settings[$plugin_id]['settings'] = $plugin_config;
             break;
           case 'tracker':
-            $this->tracker_config = $plugin_config;
+            $this->tracker_settings[$plugin_id]['settings'] = $plugin_config;
             break;
         }
       }
@@ -1571,7 +1585,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
     $plugins = array();
 
     if ($this->hasValidTracker()) {
-      $plugins['tracker'][$this->getTrackerId()] = $this->getTracker();
+      $plugins['tracker'][$this->getTrackerId()] = $this->getTrackerInstance();
     }
     $plugins['processors'] = $this->getProcessors();
     $plugins['datasources'] = $this->getDatasources();
@@ -1596,10 +1610,10 @@ class Index extends ConfigEntityBase implements IndexInterface {
    */
   public function __sleep() {
     $properties = get_object_vars($this);
-    unset($properties['datasourcePlugins']);
-    unset($properties['trackerPlugin']);
+    unset($properties['datasourceInstances']);
+    unset($properties['trackerInstance']);
     unset($properties['serverInstance']);
-    unset($properties['processorPlugins']);
+    unset($properties['processorInstances']);
     unset($properties['cache']);
     return array_keys($properties);
   }
diff --git a/src/Form/IndexForm.php b/src/Form/IndexForm.php
index 2bfca64..93d8358 100644
--- a/src/Form/IndexForm.php
+++ b/src/Form/IndexForm.php
@@ -262,7 +262,7 @@ class IndexForm extends EntityForm {
       '#title' => $this->t('Tracker'),
       '#description' => $this->t('Select the type of tracker which should be used for keeping track of item changes.'),
       '#options' => $this->getTrackerPluginManager()->getOptionsList(),
-      '#default_value' => $index->hasValidTracker() ? $index->getTracker()->getPluginId() : key($tracker_options),
+      '#default_value' => $index->hasValidTracker() ? $index->getTrackerInstance()->getPluginId() : key($tracker_options),
       '#required' => TRUE,
       '#disabled' => !$index->isNew(),
       '#ajax' => array(
@@ -392,7 +392,7 @@ class IndexForm extends EntityForm {
    */
   public function buildTrackerConfigForm(array &$form, FormStateInterface $form_state, IndexInterface $index) {
     if ($index->hasValidTracker()) {
-      $tracker = $index->getTracker();
+      $tracker = $index->getTrackerInstance();
       // @todo Create, use and save SubFormState already here, not only in
       //   validate(). Also, use proper subset of $form for first parameter?
       if ($config_form = $tracker->buildConfigurationForm(array(), $form_state)) {
@@ -484,7 +484,7 @@ class IndexForm extends EntityForm {
     //   form structure).
     $tracker_id = $form_state->getValue('tracker', NULL);
     if ($this->originalEntity->getTrackerId() == $tracker_id) {
-      $tracker = $this->originalEntity->getTracker();
+      $tracker = $this->originalEntity->getTrackerInstance();
     }
     else {
       $tracker = $this->trackerPluginManager->createInstance($tracker_id, array('index' => $this->originalEntity));
@@ -526,15 +526,17 @@ class IndexForm extends EntityForm {
     $datasources = $form_state->getValue('datasources', array());
     /** @var \Drupal\search_api\Datasource\DatasourceInterface[] $datasource_plugins */
     $datasource_plugins = $this->originalEntity->getDatasources(FALSE);
-    $datasource_configuration = array();
+    $datasource_settings = array();
     foreach ($datasources as $datasource_id) {
       $datasource = $datasource_plugins[$datasource_id];
       $datasource_form = (!empty($form['datasource_configs'][$datasource_id])) ? $form['datasource_configs'][$datasource_id] : array();
       $datasource_form_state = new SubFormState($form_state, array('datasource_configs', $datasource_id));
       $datasource->submitConfigurationForm($datasource_form, $datasource_form_state);
-      $datasource_configuration[$datasource_id] = $datasource->getConfiguration();
+
+      $datasource_settings[$datasource_id]['plugin_id'] = $datasource_id;
+      $datasource_settings[$datasource_id]['settings'] = $datasource->getConfiguration();
     }
-    $index->set('datasource_configs', $datasource_configuration);
+    $index->set('datasource_settings', $datasource_settings);
 
     // Call submitConfigurationForm() for the (possibly new) tracker.
     // @todo It seems if we change the tracker, we would validate/submit the old
@@ -544,7 +546,7 @@ class IndexForm extends EntityForm {
     //   form structure).
     $tracker_id = $form_state->getValue('tracker', NULL);
     if ($this->originalEntity->getTrackerId() == $tracker_id) {
-      $tracker = $this->originalEntity->getTracker();
+      $tracker = $this->originalEntity->getTrackerInstance();
     }
     else {
       $tracker = $this->trackerPluginManager->createInstance($tracker_id, array('index' => $this->originalEntity));
@@ -552,7 +554,12 @@ class IndexForm extends EntityForm {
 
     $tracker_form_state = new SubFormState($form_state, array('tracker_config'));
     $tracker->submitConfigurationForm($form['tracker_config'], $tracker_form_state);
-    $index->set('tracker_config', $tracker->getConfiguration());
+    $index->set('tracker_settings', array(
+      $tracker_id => array(
+        'plugin_id' => $tracker_id,
+        'settings' => $tracker->getConfiguration(),
+      )
+    ));
   }
 
   /**
diff --git a/src/Form/IndexStatusForm.php b/src/Form/IndexStatusForm.php
index 640e795..ad42155 100644
--- a/src/Form/IndexStatusForm.php
+++ b/src/Form/IndexStatusForm.php
@@ -65,7 +65,7 @@ class IndexStatusForm extends FormBase {
           'class' => array('container-inline'),
         ),
       );
-      $has_remaining_items = ($index->getTracker()->getRemainingItemsCount() > 0);
+      $has_remaining_items = ($index->getTrackerInstance()->getRemainingItemsCount() > 0);
       $all_value = $this->t('all', array(), array('context' => 'items to index'));
       $limit = array(
         '#type' => 'textfield',
diff --git a/src/IndexBatchHelper.php b/src/IndexBatchHelper.php
index 56c4d3b..144817d 100644
--- a/src/IndexBatchHelper.php
+++ b/src/IndexBatchHelper.php
@@ -137,7 +137,7 @@ class IndexBatchHelper {
     // Get the remaining item count. When no valid tracker is available then
     // the value will be set to zero which will cause the batch process to
     // stop.
-    $remaining_item_count = ($index->hasValidTracker() ? $index->getTracker()->getRemainingItemsCount() : 0);
+    $remaining_item_count = ($index->hasValidTracker() ? $index->getTrackerInstance()->getRemainingItemsCount() : 0);
 
     // Check if an explicit limit needs to be used.
     if ($context['sandbox']['limit'] > -1) {
diff --git a/src/IndexInterface.php b/src/IndexInterface.php
index a435f35..deac9e8 100644
--- a/src/IndexInterface.php
+++ b/src/IndexInterface.php
@@ -200,7 +200,7 @@ interface IndexInterface extends ConfigEntityInterface {
    * @throws \Drupal\search_api\SearchApiException
    *   Thrown if the tracker couldn't be instantiated.
    */
-  public function getTracker();
+  public function getTrackerInstance();
 
   /**
    * Determines whether this index is lying on a valid server.
diff --git a/src/Plugin/search_api/datasource/ContentEntity.php b/src/Plugin/search_api/datasource/ContentEntity.php
index 8bb2378..03d98d2 100644
--- a/src/Plugin/search_api/datasource/ContentEntity.php
+++ b/src/Plugin/search_api/datasource/ContentEntity.php
@@ -936,7 +936,7 @@ class ContentEntity extends DatasourcePluginBase {
     $entity_bundle = $entity->bundle();
 
     $index_names = \Drupal::entityQuery('search_api_index')
-      ->condition('datasources.*', $datasource_id)
+      ->condition('datasource_settings.*.plugin_id', $datasource_id)
       ->execute();
 
     if (!$index_names) {
diff --git a/src/Task/IndexTaskManager.php b/src/Task/IndexTaskManager.php
index db1b5b8..4cfafcb 100644
--- a/src/Task/IndexTaskManager.php
+++ b/src/Task/IndexTaskManager.php
@@ -99,7 +99,7 @@ class IndexTaskManager implements IndexTaskManagerInterface {
             $item_ids[] = Utility::createCombinedId($datasource_id, $raw_id);
           }
           $added = count($item_ids);
-          $index->getTracker()->trackItemsInserted($item_ids);
+          $index->getTrackerInstance()->trackItemsInserted($item_ids);
         }
       }
     }
@@ -195,7 +195,7 @@ class IndexTaskManager implements IndexTaskManagerInterface {
     if (!isset($datasource_ids)) {
       $this->state->delete($this->getIndexStateKey($index));
       if ($valid_tracker) {
-        $index->getTracker()->trackAllItemsDeleted();
+        $index->getTrackerInstance()->trackAllItemsDeleted();
       }
       return;
     }
@@ -211,7 +211,7 @@ class IndexTaskManager implements IndexTaskManagerInterface {
     foreach ($datasource_ids as $datasource_id) {
       unset($index_state['pages'][$datasource_id]);
       if ($valid_tracker) {
-        $index->getTracker()->trackAllItemsDeleted($datasource_id);
+        $index->getTrackerInstance()->trackAllItemsDeleted($datasource_id);
       }
     }
 
diff --git a/src/Tests/IntegrationTest.php b/src/Tests/IntegrationTest.php
index a14f24d..0ef3d1b 100644
--- a/src/Tests/IntegrationTest.php
+++ b/src/Tests/IntegrationTest.php
@@ -97,6 +97,54 @@ class IntegrationTest extends WebTestBase {
     $this->deleteServer();
   }
 
+
+  /**
+   * Test what happens when an index has an integer as id/label.
+   *
+   * This needs to be in a seperate index because we also want to see what
+   * happens with the content and we don't want to mess with the content entity
+   * tracking of the other index.
+   */
+  public function testIntegerIndex() {
+    $this->drupalLogin($this->adminUser);
+    $this->getTestServer();
+
+    $this->drupalCreateNode(array('type' => 'article'));
+    $this->drupalCreateNode(array('type' => 'article'));
+
+    $this->drupalGet('admin/config/search/search-api/add-index');
+
+    $this->indexId = 123;
+    $edit = array(
+        'name' => $this->indexId,
+        'id' => $this->indexId,
+        'status' => 1,
+        'description' => 'test Index:: 123~',
+        'server' => 'webtest_server',
+        'datasources[]' => array('entity:node'),
+      );
+    $this->drupalPostForm(NULL, $edit, $this->t('Save'));
+    $this->assertText($this->t('The index was successfully saved.'));
+    $this->assertText($this->t('Successfully tracked @count items for this index.', array('@count' => 2)));
+    $this->assertEqual(2, $this->countTrackedItems());
+
+    $this->enableAllProcessors();
+    $this->checkFieldLabels();
+
+    $this->addFieldsToIndex();
+    $this->removeFieldsFromIndex();
+
+    $this->configureFilter();
+    $this->configureFilterPage();
+    $this->checkProcessorChanges();
+    $this->changeProcessorFieldBoost();
+
+    $this->setReadOnly();
+    $this->disableEnableIndex();
+    $this->changeIndexDatasource();
+    $this->changeIndexServer();
+  }
+
   /**
    * Tests creating a search server via the UI.
    */
@@ -382,7 +430,7 @@ class IntegrationTest extends WebTestBase {
    *   The number of tracked items in the test index.
    */
   protected function countTrackedItems() {
-    return $this->getIndex()->getTracker()->getTotalItemsCount();
+    return $this->getIndex()->getTrackerInstance()->getTotalItemsCount();
   }
 
   /**
@@ -392,7 +440,7 @@ class IntegrationTest extends WebTestBase {
    *   The number of unindexed items in the test index.
    */
   protected function countRemainingItems() {
-    return $this->getIndex()->getTracker()->getRemainingItemsCount();
+    return $this->getIndex()->getTrackerInstance()->getRemainingItemsCount();
   }
 
   /**
@@ -723,7 +771,7 @@ class IntegrationTest extends WebTestBase {
 
     $this->drupalPostForm($index_path, array(), $this->t('Index now'));
 
-    $remaining_after = $index->getTracker()->getRemainingItemsCount();
+    $remaining_after = $index->getTrackerInstance()->getRemainingItemsCount();
     $this->assertEqual(0, $remaining_after, 'Items were indexed after removing the "read only" flag.');
 
   }
diff --git a/src/Tests/LanguageIntegrationTest.php b/src/Tests/LanguageIntegrationTest.php
index 5dfec22..0dc654e 100644
--- a/src/Tests/LanguageIntegrationTest.php
+++ b/src/Tests/LanguageIntegrationTest.php
@@ -128,7 +128,7 @@ class LanguageIntegrationTest extends WebTestBase {
   protected function countTrackedItems() {
     /** @var \Drupal\search_api\IndexInterface $index */
     $index = Index::load($this->indexId);
-    return $index->getTracker()->getTotalItemsCount();
+    return $index->getTrackerInstance()->getTotalItemsCount();
   }
 
   /**
diff --git a/src/Tests/Processor/ContentAccessTest.php b/src/Tests/Processor/ContentAccessTest.php
index b301cd4..b0320b9 100644
--- a/src/Tests/Processor/ContentAccessTest.php
+++ b/src/Tests/Processor/ContentAccessTest.php
@@ -109,7 +109,23 @@ class ContentAccessTest extends ProcessorTestBase {
     $this->nodes[2]->save();
 
     // Also index users, to verify that they are unaffected by the processor.
-    $this->index->set('datasources', array('entity:comment', 'entity:node', 'entity:user'));
+    $this->index->set(
+      'datasource_settings',
+      array(
+        'entity:comment' => array(
+          'plugin_id' => 'entity:comment',
+          'settings' => array(),
+        ),
+        'entity:node' => array(
+          'plugin_id' => 'entity:node',
+          'settings' => array(),
+        ),
+        'entity:user' => array(
+          'plugin_id' => 'entity:user',
+          'settings' => array(),
+        ),
+      )
+    );
     $this->index->save();
 
     \Drupal::getContainer()->get('search_api.index_task_manager')->addItemsAll($this->index);
@@ -125,6 +141,8 @@ class ContentAccessTest extends ProcessorTestBase {
     user_role_grant_permissions('anonymous', array('access content', 'access comments'));
     $this->index->reindex();
     $this->index->indexItems();
+    $this->assertEqual(5, $this->index->getTrackerInstance()->getIndexedItemsCount(), '5 items indexed, as expected.');
+
     $query = Utility::createQuery($this->index);
     $result = $query->execute();
 
@@ -138,6 +156,8 @@ class ContentAccessTest extends ProcessorTestBase {
     user_role_grant_permissions('anonymous', array('access comments'));
     $this->index->reindex();
     $this->index->indexItems();
+    $this->assertEqual(5, $this->index->getTrackerInstance()->getIndexedItemsCount(), '5 items indexed, as expected.');
+
     $query = Utility::createQuery($this->index);
     $result = $query->execute();
 
@@ -154,6 +174,7 @@ class ContentAccessTest extends ProcessorTestBase {
     $this->nodes[3] = Node::create(array('status' => NODE_NOT_PUBLISHED, 'type' => 'page', 'title' => 'foo', 'uid' => 2));
     $this->nodes[3]->save();
     $this->index->indexItems();
+    $this->assertEqual(7, $this->index->getTrackerInstance()->getIndexedItemsCount(), '7 items indexed, as expected.');
 
     $query = Utility::createQuery($this->index);
     $query->setOption('search_api_access_account', $authenticated_user);
diff --git a/src/Tests/Processor/ProcessorIntegrationTest.php b/src/Tests/Processor/ProcessorIntegrationTest.php
index ad617c8..24ea7d4 100644
--- a/src/Tests/Processor/ProcessorIntegrationTest.php
+++ b/src/Tests/Processor/ProcessorIntegrationTest.php
@@ -32,7 +32,12 @@ class ProcessorIntegrationTest extends WebTestBase {
       'name' => 'Test index',
       'id' => $this->indexId,
       'status' => 1,
-      'datasources' => array('entity:node'),
+      'datasource_settings' => array(
+        'entity:node' => array(
+          'plugin_id' => 'entity:user',
+          'settings' => array(),
+        ),
+      ),
     ))->save();
   }
 
diff --git a/src/Tests/Processor/ProcessorTestBase.php b/src/Tests/Processor/ProcessorTestBase.php
index 2809c31..a9ccdeb 100644
--- a/src/Tests/Processor/ProcessorTestBase.php
+++ b/src/Tests/Processor/ProcessorTestBase.php
@@ -87,7 +87,16 @@ abstract class ProcessorTestBase extends EntityUnitTestBase {
       'id' => 'index',
       'name' => 'Index name',
       'status' => TRUE,
-      'datasources' => array('entity:comment', 'entity:node'),
+      'datasource_settings' => array(
+        'entity:comment' => array(
+          'plugin_id' => 'entity:comment',
+          'settings' => array(),
+        ),
+        'entity:node' => array(
+          'plugin_id' => 'entity:node',
+          'settings' => array(),
+        ),
+      ),
       'server' => 'server',
       'tracker' => 'default',
     ));
diff --git a/src/Tests/Processor/RenderedItemTest.php b/src/Tests/Processor/RenderedItemTest.php
index 8a920e4..4b561fc 100644
--- a/src/Tests/Processor/RenderedItemTest.php
+++ b/src/Tests/Processor/RenderedItemTest.php
@@ -115,6 +115,35 @@ class RenderedItemTest extends ProcessorTestBase {
   }
 
   /**
+   * Tests that the processor is added correctly.
+   */
+  public function testAddProcessor() {
+    $processors = $this->index->getProcessors();
+    $this->assertTrue(
+      array_key_exists('rendered_item', $processors),
+      'Processor successfully added.'
+    );
+
+    $items = array();
+    foreach ($this->nodes as $node) {
+      $items[] = array(
+        'datasource' => 'entity:node',
+        'item' => $node->getTypedData(),
+        'item_id' => $node->id(),
+        'text' => 'node text' . $node->id(),
+      );
+    }
+    $items = $this->generateItems($items);
+
+    foreach ($items as $item) {
+      $this->assertTrue(
+        array_key_exists('rendered_item', $item->getFields()),
+        'Field successfully added.'
+      );
+    }
+  }
+
+  /**
    * Tests whether the rendered_item field is correctly filled by the processor.
    */
   public function testPreprocessIndexItems() {
diff --git a/src/Tests/WebTestBase.php b/src/Tests/WebTestBase.php
index 8b85ea6..4dd9113 100644
--- a/src/Tests/WebTestBase.php
+++ b/src/Tests/WebTestBase.php
@@ -169,7 +169,12 @@ abstract class WebTestBase extends SimpletestWebTestBase {
         'name' => $name,
         'description' => $name . ' description',
         'server' => $server_id,
-        'datasources' => array($datasource_id),
+        'datasource_settings' => array(
+          $datasource_id => array(
+            'plugin_id' => $datasource_id,
+            'settings' => array()
+          )
+        ),
       ));
       $index->save();
       $this->indexId = $index->id();
diff --git a/src/UnsavedIndexConfiguration.php b/src/UnsavedIndexConfiguration.php
index 8fe07be..ebbd30d 100644
--- a/src/UnsavedIndexConfiguration.php
+++ b/src/UnsavedIndexConfiguration.php
@@ -249,8 +249,8 @@ class UnsavedIndexConfiguration implements IndexInterface, UnsavedConfigurationI
   /**
    * {@inheritdoc}
    */
-  public function getTracker() {
-    return $this->entity->getTracker();
+  public function getTrackerInstance() {
+    return $this->entity->getTrackerInstance();
   }
 
   /**
diff --git a/tests/search_api_test_db/config/install/search_api.index.database_search_index.yml b/tests/search_api_test_db/config/install/search_api.index.database_search_index.yml
index 4f42d29..04cea6b 100644
--- a/tests/search_api_test_db/config/install/search_api.index.database_search_index.yml
+++ b/tests/search_api_test_db/config/install/search_api.index.database_search_index.yml
@@ -2,7 +2,7 @@ id: database_search_index
 name: 'Test index'
 description: 'An index used for testing'
 read_only: false
-fields:
+field_settings:
   id:
     label: ID
     type: integer
@@ -54,11 +54,14 @@ processors:
 options:
   cron_limit: -1
   index_directly: false
-datasources:
-  - 'entity:entity_test'
-datasource_configs: {  }
-tracker: default
-tracker_config: {  }
+datasource_settings:
+  'entity:entity_test':
+    plugin_id: 'entity:entity_test'
+    settings: {  }
+tracker_settings:
+  'default':
+    plugin_id: default
+    settings: {  }
 server: database_search_server
 status: true
 langcode: en
diff --git a/tests/src/Kernel/CliTest.php b/tests/src/Kernel/CliTest.php
index 70fd5cc..95c3395 100644
--- a/tests/src/Kernel/CliTest.php
+++ b/tests/src/Kernel/CliTest.php
@@ -94,15 +94,20 @@ class CliTest extends KernelTestBase {
       'name' => 'Test index',
       'id' => 'index',
       'status' => 1,
-      'datasources' => array('entity:entity_test'),
+      'datasource_settings' => array(
+        'entity:entity_test' => array(
+          'plugin_id' => 'entity:entity_test',
+          'settings' => array(),
+        ),
+      ),
       'tracker' => 'default',
       'server' => $this->server->id(),
       'options' => array('index_directly' => TRUE),
     ));
     $index->save();
 
-    $total_items = $index->getTracker()->getTotalItemsCount();
-    $indexed_items = $index->getTracker()->getIndexedItemsCount();
+    $total_items = $index->getTrackerInstance()->getTotalItemsCount();
+    $indexed_items = $index->getTrackerInstance()->getIndexedItemsCount();
 
     $this->assertEquals($total_items, 2, 'The 2 items are tracked.');
     $this->assertEquals($indexed_items, 0, 'No items are indexed');
@@ -122,8 +127,8 @@ class CliTest extends KernelTestBase {
       'category' => 'item_category'
     ))->save();
 
-    $total_items = $index->getTracker()->getTotalItemsCount();
-    $indexed_items = $index->getTracker()->getIndexedItemsCount();
+    $total_items = $index->getTrackerInstance()->getTotalItemsCount();
+    $indexed_items = $index->getTrackerInstance()->getIndexedItemsCount();
 
     $this->assertEquals($total_items, 4, 'All 4 items are tracked.');
     $this->assertEquals($indexed_items, 2, '2 items are indexed');
diff --git a/tests/src/Kernel/DependencyRemovalTest.php b/tests/src/Kernel/DependencyRemovalTest.php
index 9245486..717ea0d 100644
--- a/tests/src/Kernel/DependencyRemovalTest.php
+++ b/tests/src/Kernel/DependencyRemovalTest.php
@@ -57,9 +57,17 @@ class DependencyRemovalTest extends KernelTestBase {
     $this->index = Index::create(array(
       'id' => 'test_index',
       'name' => 'Test index',
-      'tracker' => 'default',
-      'datasources' => array(
-        'entity:user',
+      'tracker_settings' => array(
+        'default' => array(
+          'plugin_id' => 'default',
+          'settings' => array()
+        )
+      ),
+      'datasource_settings' => array(
+        'entity:user' => array(
+          'plugin_id' => 'entity:user',
+          'settings' => array(),
+        )
       ),
     ));
 
@@ -79,13 +87,13 @@ class DependencyRemovalTest extends KernelTestBase {
    * If the dependency does not get removed, proper cascading to the index is
    * also verified.
    *
-   * @param bool $remove_dependency
+   * @param bool $dependency_removal_return_value
    *   Whether to remove the dependency from the backend when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testBackendDependency($remove_dependency) {
+  public function testBackendDependency($dependency_removal_return_value) {
     $dependency_key = $this->dependency->getConfigDependencyKey();
     $dependency_name = $this->dependency->getConfigDependencyName();
 
@@ -125,7 +133,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_backend\Plugin\search_api\backend\TestBackend::onDependencyRemoval().
     $key = 'search_api_test_backend.dependencies.remove';
-    \Drupal::state()->set($key, $remove_dependency);
+    \Drupal::state()->set($key, $dependency_removal_return_value);
 
     // Delete the backend's dependency.
     $this->dependency->delete();
@@ -139,7 +147,7 @@ class DependencyRemovalTest extends KernelTestBase {
     $storage->resetCache();
     $server = $storage->load($server->id());
 
-    if ($remove_dependency) {
+    if ($dependency_removal_return_value) {
       $this->assertInstanceOf('Drupal\search_api\ServerInterface', $server, 'Server was not removed');
       $this->assertArrayNotHasKey('dependencies', $server->get('backend_config'), 'Backend config was adapted');
       // @todo Logically, this should not be changed: if the server does not get
@@ -161,28 +169,33 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a datasource with a dependency that gets removed.
    *
-   * @param bool $remove_dependency
+   * @param bool $dependency_removal_return_value
    *   Whether to remove the dependency from the datasource when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testDatasourceDependency($remove_dependency) {
+  public function testDatasourceDependency($dependency_removal_return_value) {
     // Add the datasource to the index and save it. The datasource configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
     $dependency_key = $this->dependency->getConfigDependencyKey();
     $dependency_name = $this->dependency->getConfigDependencyName();
-    $this->index->set('datasources', array(
-      'entity:user',
-      'search_api_test_dependencies',
-    ));
-    $this->index->set('datasource_configs', array(
-      'search_api_test_dependencies' => array(
-        $dependency_key => array(
-          $dependency_name,
+    $this->index->set(
+      'datasource_settings',
+      array(
+        'entity:user' => array(
+          'plugin_id' => 'entity:user',
+          'settings' => array(),
+        ),
+        'search_api_test_dependencies' => array(
+          'plugin_id' => 'search_api_test_dependencies',
+          'settings' => array(
+            $dependency_key => array(
+              $dependency_name,
+            ),
+          ),
         ),
-      ),
     ));
     $this->index->save();
 
@@ -194,7 +207,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\datasource\TestDatasource::onDependencyRemoval().
     $key = 'search_api_test_dependencies.datasource.remove';
-    \Drupal::state()->set($key, $remove_dependency);
+    \Drupal::state()->set($key, $dependency_removal_return_value);
 
     // Delete the datasource's dependency.
     $this->dependency->delete();
@@ -210,15 +223,14 @@ class DependencyRemovalTest extends KernelTestBase {
 
     // Depending on whether the plugin should have removed the dependency or
     // not, make sure the right action was taken.
-    $datasources = $this->index->get('datasources');
-    $datasource_configs = $this->index->get('datasource_configs');
-    if ($remove_dependency) {
-      $this->assertContains('search_api_test_dependencies', $datasources, 'Datasource not removed');
-      $this->assertEmpty($datasource_configs['search_api_test_dependencies'], 'Datasource settings adapted');
+    $datasources = $this->index->get('datasource_settings');
+    if ($dependency_removal_return_value) {
+      $this->assertContains('search_api_test_dependencies', array_keys($datasources), 'Datasource not removed');
+      $this->assertEmpty($datasources['search_api_test_dependencies']['settings'], 'Datasource settings adapted');
     }
     else {
-      $this->assertNotContains('search_api_test_dependencies', $datasources, 'Datasource removed');
-      $this->assertArrayNotHasKey('search_api_test_dependencies', $datasource_configs, 'Datasource config removed');
+      $this->assertNotContains('search_api_test_dependencies', array_keys($datasources), 'Datasource removed');
+      $this->assertArrayNotHasKey('search_api_test_dependencies', $datasources, 'Datasource config removed');
     }
   }
 
@@ -231,15 +243,13 @@ class DependencyRemovalTest extends KernelTestBase {
     // server.
     $dependency_key = $this->dependency->getConfigDependencyKey();
     $dependency_name = $this->dependency->getConfigDependencyName();
-    $this->index->set('datasources', array(
-      'search_api_test_dependencies',
-    ));
-    $this->index->set('datasource_configs', array(
+    $this->index->set('datasource_settings', array(
       'search_api_test_dependencies' => array(
-        $dependency_key => array(
-          $dependency_name,
+        'plugin_id' => 'search_api_test_dependencies',
+        'settings' => array(
+          $dependency_key => array($dependency_name)
         ),
-      ),
+      )
     ));
     $this->index->save();
 
@@ -263,13 +273,13 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a processor with a dependency that gets removed.
    *
-   * @param bool $remove_dependency
+   * @param bool $dependency_removal_return_value
    *   Whether to remove the dependency from the processor when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testProcessorDependency($remove_dependency) {
+  public function testProcessorDependency($dependency_removal_return_value) {
     // Add the processor to the index and save it. The processor configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
@@ -295,7 +305,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\processor\TestProcessor::onDependencyRemoval().
     $key = 'search_api_test_dependencies.processor.remove';
-    \Drupal::state()->set($key, $remove_dependency);
+    \Drupal::state()->set($key, $dependency_removal_return_value);
 
     // Delete the processor's dependency.
     $this->dependency->delete();
@@ -312,7 +322,7 @@ class DependencyRemovalTest extends KernelTestBase {
     // Depending on whether the plugin should have removed the dependency or
     // not, make sure the right action was taken.
     $processors = $this->index->get('processors');
-    if ($remove_dependency) {
+    if ($dependency_removal_return_value) {
       $this->assertArrayHasKey('search_api_test_dependencies', $processors, 'Processor not removed');
       $this->assertEmpty($processors['search_api_test_dependencies']['settings'], 'Processor settings adapted');
     }
@@ -324,23 +334,27 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Tests a tracker with a dependency that gets removed.
    *
-   * @param bool $remove_dependency
+   * @param bool $dependency_removal_return_value
    *   Whether to remove the dependency from the tracker when the object
    *   depended on is deleted.
    *
    * @dataProvider dependencyTestDataProvider
    */
-  public function testTrackerDependency($remove_dependency) {
+  public function testTrackerDependency($dependency_removal_return_value) {
     // Set the tracker for the index and save it. The tracker configuration
     // contains the dependencies it will return – in our case, we use the test
     // server.
     $dependency_key = $this->dependency->getConfigDependencyKey();
     $dependency_name = $this->dependency->getConfigDependencyName();
-    $this->index->set('tracker', 'search_api_test_dependencies');
-    $this->index->set('tracker_config', array(
-      $dependency_key => array(
-        $dependency_name,
-      ),
+    $this->index->set('tracker_settings', array(
+      'search_api_test_dependencies' => array(
+        'plugin_id' => 'search_api_test_dependencies',
+        'settings' => array(
+          $dependency_key => array(
+            $dependency_name,
+          ),
+        )
+      )
     ));
     $this->index->save();
 
@@ -352,10 +366,10 @@ class DependencyRemovalTest extends KernelTestBase {
     // dependency should be removed or not. See
     // \Drupal\search_api_test_dependencies\Plugin\search_api\tracker\TestTracker::onDependencyRemoval().
     $key = 'search_api_test_dependencies.tracker.remove';
-    \Drupal::state()->set($key, $remove_dependency);
+    \Drupal::state()->set($key, $dependency_removal_return_value);
     // If the index resets the tracker, it needs to know the ID of the default
     // tracker.
-    if (!$remove_dependency) {
+    if (!$dependency_removal_return_value) {
       \Drupal::configFactory()->getEditable('search_api.settings')
         ->set('default_tracker', 'default')
         ->save();
@@ -375,9 +389,11 @@ class DependencyRemovalTest extends KernelTestBase {
 
     // Depending on whether the plugin should have removed the dependency or
     // not, make sure the right action was taken.
-    $tracker = $this->index->get('tracker');
-    $tracker_config = $this->index->get('tracker_config');
-    if ($remove_dependency) {
+    $config = $this->index->get('tracker_settings');
+    $plugins = array_keys($config);
+    $tracker = $config[$plugins[0]]['plugin_id'];
+    $tracker_config = $config[$plugins[0]]['settings'];
+    if ($dependency_removal_return_value) {
       $this->assertEquals('search_api_test_dependencies', $tracker, 'Tracker not reset');
       $this->assertEmpty($tracker_config, 'Tracker settings adapted');
     }
@@ -392,9 +408,15 @@ class DependencyRemovalTest extends KernelTestBase {
    */
   public function testModuleDependency() {
     // Test with all types of plugins at once.
-    $this->index->set('datasources', array(
-      'entity:user',
-      'search_api_test_dependencies',
+    $this->index->set('datasource_settings', array(
+      'entity:user' => array(
+        'plugin_id' => 'entity:user',
+        'settings' => array(),
+      ),
+      'search_api_test_dependencies' => array(
+        'plugin_id' => 'search_api_test_dependencies',
+        'settings' => array(),
+      ),
     ));
     $this->index->set('processors', array(
       'search_api_test_dependencies' => array(
@@ -439,13 +461,24 @@ class DependencyRemovalTest extends KernelTestBase {
   /**
    * Data provider for this class's test methods.
    *
+   * If $dependency_removal_return_value is TRUE, in
+   * Plugin::onDependencyRemoval() it clears its configuration (and thus its
+   * dependency, in those test plugins) and returns TRUE, which the index will
+   * take as "all OK, dependency removed" and leave the plugin where it is,
+   * only with updated configuration.
+   *
+   * If $dependency_removal_return_value is FALSE, Plugin::onDependencyRemoval()
+   * will do nothing and just return FALSE, the index says "oh, that plugin
+   * still has that removed depenency, so I should better remove the plugin"
+   * and the plugin gets removed.
+   *
    * @return array
    *   An array of argument arrays for this class's test methods.
    */
   public function dependencyTestDataProvider() {
     return array(
-      'Remove dependency' => array(TRUE),
-      'Keep dependency' => array(FALSE),
+      'Keep dependency' => array(TRUE),
+      'Remove dependency' => array(FALSE),
     );
   }
 
diff --git a/tests/src/Kernel/LanguageKernelTest.php b/tests/src/Kernel/LanguageKernelTest.php
index 671a957..75c8bc6 100644
--- a/tests/src/Kernel/LanguageKernelTest.php
+++ b/tests/src/Kernel/LanguageKernelTest.php
@@ -108,8 +108,18 @@ class LanguageKernelTest extends KernelTestBase {
       'name' => 'Test Index',
       'id' => 'test_index',
       'status' => 1,
-      'datasources' => array('entity:' . $this->testEntityTypeId),
-      'tracker' => 'default',
+      'datasource_settings' => array(
+        'entity:' . $this->testEntityTypeId => array(
+          'plugin_id' => 'entity:' . $this->testEntityTypeId,
+          'settings' => array(),
+        ),
+      ),
+      'tracker_settings' => array(
+        'default' => array(
+          'plugin_id' => 'default',
+          'settings' => array(),
+        )
+      ),
       'server' => $this->server->id(),
       'options' => array('index_directly' => FALSE),
     ));
@@ -153,10 +163,10 @@ class LanguageKernelTest extends KernelTestBase {
     $this->assertEquals($expected, $datasource_item_ids, 'Datasource returns correct item ids.');
 
     // Test indexing the new entity.
-    $this->assertEquals(0, $this->index->getTracker()->getIndexedItemsCount(), 'The index is empty.');
-    $this->assertEquals(2, $this->index->getTracker()->getTotalItemsCount(), 'There are two items to be indexed.');
+    $this->assertEquals(0, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'The index is empty.');
+    $this->assertEquals(2, $this->index->getTrackerInstance()->getTotalItemsCount(), 'There are two items to be indexed.');
     $this->index->indexItems();
-    $this->assertEquals(2, $this->index->getTracker()->getIndexedItemsCount(), 'Two items have been indexed.');
+    $this->assertEquals(2, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'Two items have been indexed.');
 
     // Now, make the first entity language-specific by assigning a language.
     $default_langcode = $this->langcodes[0];
@@ -175,8 +185,8 @@ class LanguageKernelTest extends KernelTestBase {
     $this->assertEquals($expected, $datasource_item_ids, 'Datasource returns correct item ids.');
 
     // Test that the index needs to be updated.
-    $this->assertEquals(1, $this->index->getTracker()->getIndexedItemsCount(), 'The updated item needs to be reindexed.');
-    $this->assertEquals(2, $this->index->getTracker()->getTotalItemsCount(), 'There are two items in total.');
+    $this->assertEquals(1, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'The updated item needs to be reindexed.');
+    $this->assertEquals(2, $this->index->getTrackerInstance()->getTotalItemsCount(), 'There are two items in total.');
 
     // Set two translations for the first entity and test that the datasource
     // returns three separate item IDs, one for each translation.
@@ -197,8 +207,8 @@ class LanguageKernelTest extends KernelTestBase {
     $this->assertEquals($expected, $datasource_item_ids, 'Datasource returns correct item ids for a translated entity.');
 
     // Test that the index needs to be updated.
-    $this->assertEquals(1, $this->index->getTracker()->getIndexedItemsCount(), 'The updated items needs to be reindexed.');
-    $this->assertEquals(4, $this->index->getTracker()->getTotalItemsCount(), 'There are four items in total.');
+    $this->assertEquals(1, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'The updated items needs to be reindexed.');
+    $this->assertEquals(4, $this->index->getTrackerInstance()->getTotalItemsCount(), 'There are four items in total.');
 
     // Delete one translation and test that the datasource returns only three
     // items.
@@ -215,10 +225,10 @@ class LanguageKernelTest extends KernelTestBase {
     $this->assertEquals($expected, $datasource_item_ids, 'Datasource returns correct item ids for a translated entity.');
 
     // Test reindexing.
-    $this->assertEquals(3, $this->index->getTracker()->getTotalItemsCount(), 'There are three items in total.');
-    $this->assertEquals(1, $this->index->getTracker()->getIndexedItemsCount(), 'The updated items needs to be reindexed.');
+    $this->assertEquals(3, $this->index->getTrackerInstance()->getTotalItemsCount(), 'There are three items in total.');
+    $this->assertEquals(1, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'The updated items needs to be reindexed.');
     $this->index->indexItems();
-    $this->assertEquals(3, $this->index->getTracker()->getIndexedItemsCount(), 'Three items are indexed.');
+    $this->assertEquals(3, $this->index->getTrackerInstance()->getIndexedItemsCount(), 'Three items are indexed.');
   }
 
 }
diff --git a/tests/src/Kernel/ServerTaskTest.php b/tests/src/Kernel/ServerTaskTest.php
index a31595d..e83a87f 100644
--- a/tests/src/Kernel/ServerTaskTest.php
+++ b/tests/src/Kernel/ServerTaskTest.php
@@ -91,7 +91,12 @@ class ServerTaskTest extends KernelTestBase {
       'name' => 'Test index',
       'id' => 'test_index',
       'status' => 1,
-      'datasources' => array('entity:user'),
+      'datasource_settings' => array(
+        'entity:user' => array(
+          'plugin_id' => 'entity:user',
+          'settings' => array(),
+        ),
+      ),
       'tracker' => 'default',
       'server' => $this->server->id(),
       'options' => array('index_directly' => FALSE),