diff --git a/apps/advanced/backend/config/main.php b/apps/advanced/backend/config/main.php
index 7d82a3415d..a0b5fc9932 100644
--- a/apps/advanced/backend/config/main.php
+++ b/apps/advanced/backend/config/main.php
@@ -10,6 +10,7 @@ return [
     'id' => 'app-backend',
     'basePath' => dirname(__DIR__),
     'controllerNamespace' => 'backend\controllers',
+    'bootstrap' => ['log'],
     'modules' => [],
     'components' => [
         'user' => [
diff --git a/apps/advanced/console/config/main.php b/apps/advanced/console/config/main.php
index f91278d262..ec60922f97 100644
--- a/apps/advanced/console/config/main.php
+++ b/apps/advanced/console/config/main.php
@@ -9,6 +9,7 @@ $params = array_merge(
 return [
     'id' => 'app-console',
     'basePath' => dirname(__DIR__),
+    'bootstrap' => ['log'],
     'controllerNamespace' => 'console\controllers',
     'modules' => [],
     'components' => [
diff --git a/apps/advanced/frontend/config/main.php b/apps/advanced/frontend/config/main.php
index e891885551..1ed8305ec8 100644
--- a/apps/advanced/frontend/config/main.php
+++ b/apps/advanced/frontend/config/main.php
@@ -9,6 +9,7 @@ $params = array_merge(
 return [
     'id' => 'app-frontend',
     'basePath' => dirname(__DIR__),
+    'bootstrap' => ['log'],
     'controllerNamespace' => 'frontend\controllers',
     'components' => [
         'user' => [
diff --git a/apps/basic/config/console.php b/apps/basic/config/console.php
index 88c43c5264..462f35bd6c 100644
--- a/apps/basic/config/console.php
+++ b/apps/basic/config/console.php
@@ -8,6 +8,7 @@ $db = require(__DIR__ . '/db.php');
 return [
     'id' => 'basic-console',
     'basePath' => dirname(__DIR__),
+    'bootstrap' => ['log'],
     'controllerNamespace' => 'app\commands',
     'extensions' => require(__DIR__ . '/../vendor/yiisoft/extensions.php'),
     'components' => [
diff --git a/apps/basic/config/web.php b/apps/basic/config/web.php
index 845a521c4b..fb9c6791c9 100644
--- a/apps/basic/config/web.php
+++ b/apps/basic/config/web.php
@@ -6,6 +6,7 @@ $db = require(__DIR__ . '/db.php');
 $config = [
     'id' => 'basic',
     'basePath' => dirname(__DIR__),
+    'bootstrap' => ['log'],
     'extensions' => require(__DIR__ . '/../vendor/yiisoft/extensions.php'),
     'components' => [
         'cache' => [
diff --git a/extensions/debug/Module.php b/extensions/debug/Module.php
index 6a61ebe1f3..6271bdc4cc 100644
--- a/extensions/debug/Module.php
+++ b/extensions/debug/Module.php
@@ -71,9 +71,15 @@ class Module extends \yii\base\Module implements BootstrapInterface
     public function init()
     {
         parent::init();
-
         $this->dataPath = Yii::getAlias($this->dataPath);
+        $this->initPanels();
+    }
 
+    /**
+     * Initializes panels.
+     */
+    protected function initPanels()
+    {
         // merge custom panels and core panels so that they are ordered mainly by custom panels
         if (empty($this->panels)) {
             $this->panels = $this->corePanels();
diff --git a/framework/base/Application.php b/framework/base/Application.php
index 82724814cd..e6778b0589 100644
--- a/framework/base/Application.php
+++ b/framework/base/Application.php
@@ -137,29 +137,32 @@ abstract class Application extends Module
      * [
      *     'name' => 'extension name',
      *     'version' => 'version number',
-     *     'bootstrap' => 'BootstrapClassName',
+     *     'bootstrap' => 'BootstrapClassName',  // optional, may also be a configuration array
      *     'alias' => [
      *         '@alias1' => 'to/path1',
      *         '@alias2' => 'to/path2',
      *     ],
      * ]
      * ~~~
+     *
+     * The "bootstrap" class listed above will be instantiated during the application
+     * [[bootstrap()|bootstrapping process]]. If the class implements [[BootstrapInterface]],
+     * its [[BootstrapInterface::bootstrap()|bootstrap()]] method will be also be called.
      */
     public $extensions = [];
     /**
-     * @var array list of bootstrap components that should be run right after
-     * the application is configured.
+     * @var array list of components that should be run during the application [[bootstrap()|bootstrapping process]].
      *
-     * Each bootstrap component may be specified in one of the following formats:
+     * Each component may be specified in one of the following formats:
      *
      * - an application component ID as specified via [[components]].
      * - a module ID as specified via [[modules]].
      * - a class name.
      * - a configuration array.
      *
-     * Note that a bootstrap component must implement [[BootstrapInterface]], or an exception will be thrown.
-     * The [[BootstrapInterface::bootstrap()]] method of each bootstrap component will be called
-     * when the component is instantiated and run in in [[bootstrap()]].
+     * During the bootstrapping process, each component will be instantiated. If the component class
+     * implements [[BootstrapInterface]], its [[BootstrapInterface::bootstrap()|bootstrap()]] method
+     * will be also be called.
      */
     public $bootstrap = [];
     /**
@@ -245,7 +248,6 @@ abstract class Application extends Module
     public function init()
     {
         $this->state = self::STATE_INIT;
-        $this->get('log');
         $this->bootstrap();
     }
 
@@ -253,7 +255,6 @@ abstract class Application extends Module
      * Initializes extensions and executes bootstrap components.
      * This method is called by [[init()]] after the application has been fully configured.
      * If you override this method, make sure you also call the parent implementation.
-     * @throws InvalidConfigException if a bootstrap component does not implement BootstrapInterface
      */
     protected function bootstrap()
     {
@@ -266,10 +267,10 @@ abstract class Application extends Module
             if (isset($extension['bootstrap'])) {
                 $component = Yii::createObject($extension['bootstrap']);
                 if ($component instanceof BootstrapInterface) {
+                    Yii::trace("Bootstrap with " . get_class($component) . '::bootstrap()', __METHOD__);
                     $component->bootstrap($this);
                 } else {
-                    $class = is_array($extension['bootstrap']) ? $extension['bootstrap']['class'] : $extension['bootstrap'];
-                    throw new InvalidConfigException("$class must implement \\yii\\base\\BootstrapInterface");
+                    Yii::trace("Bootstrap with " . get_class($component), __METHOD__);
                 }
             }
         }
@@ -280,6 +281,8 @@ abstract class Application extends Module
                     $component = $this->get($class);
                 } elseif ($this->hasModule($class)) {
                     $component = $this->getModule($class);
+                } elseif (strpos($class, '\\') === false) {
+                    throw new InvalidConfigException("Unknown bootstrap component ID: $class");
                 }
             }
             if (!isset($component)) {
@@ -287,9 +290,10 @@ abstract class Application extends Module
             }
 
             if ($component instanceof BootstrapInterface) {
+                Yii::trace("Bootstrap with " . get_class($component) . '::bootstrap()', __METHOD__);
                 $component->bootstrap($this);
             } else {
-                throw new InvalidConfigException((is_array($class) ? $class['class'] : $class) . " must implement \\yii\\base\\BootstrapInterface");
+                Yii::trace("Bootstrap with " . get_class($component), __METHOD__);
             }
         }
     }