diff --git a/public/index.php b/public/index.php
index 8cf5ce347c82..6d78241411ba 100644
--- a/public/index.php
+++ b/public/index.php
@@ -36,18 +36,20 @@
 
 $paths = new Config\Paths();
 
-// Location of the framework bootstrap file.
-require rtrim($paths->systemDirectory, '\\/ ') . DIRECTORY_SEPARATOR . 'bootstrap.php';
-
 // Load environment settings from .env files into $_SERVER and $_ENV
-require_once SYSTEMPATH . 'Config/DotEnv.php';
-(new CodeIgniter\Config\DotEnv(ROOTPATH))->load();
+require_once $paths->systemDirectory . '/Config/DotEnv.php';
+(new CodeIgniter\Config\DotEnv($paths->appDirectory . '/../'))->load();
 
 // Define ENVIRONMENT
 if (! defined('ENVIRONMENT')) {
-    define('ENVIRONMENT', env('CI_ENVIRONMENT', 'production'));
+    $env = $_ENV['CI_ENVIRONMENT'] ?? $_SERVER['CI_ENVIRONMENT'] ?? getenv('CI_ENVIRONMENT');
+    define('ENVIRONMENT', ($env !== false) ? $env : 'production');
+    unset($env);
 }
 
+// Location of the framework bootstrap file.
+require rtrim($paths->systemDirectory, '\\/ ') . DIRECTORY_SEPARATOR . 'bootstrap.php';
+
 // Load Config Cache
 // $factoriesCache = new \CodeIgniter\Cache\FactoriesCache();
 // $factoriesCache->load('config');
diff --git a/spark b/spark
index 7029eee1f775..7428b8a392a5 100755
--- a/spark
+++ b/spark
@@ -71,18 +71,20 @@ require FCPATH . '../app/Config/Paths.php';
 
 $paths = new Config\Paths();
 
-// Location of the framework bootstrap file.
-require rtrim($paths->systemDirectory, '\\/ ') . DIRECTORY_SEPARATOR . 'bootstrap.php';
-
 // Load environment settings from .env files into $_SERVER and $_ENV
-require_once SYSTEMPATH . 'Config/DotEnv.php';
-(new CodeIgniter\Config\DotEnv(ROOTPATH))->load();
+require_once $paths->systemDirectory . '/Config/DotEnv.php';
+(new CodeIgniter\Config\DotEnv($paths->appDirectory . '/../'))->load();
 
 // Define ENVIRONMENT
 if (! defined('ENVIRONMENT')) {
-    define('ENVIRONMENT', env('CI_ENVIRONMENT', 'production'));
+    $env = $_ENV['CI_ENVIRONMENT'] ?? $_SERVER['CI_ENVIRONMENT'] ?? getenv('CI_ENVIRONMENT');
+    define('ENVIRONMENT', ($env !== false) ? $env : 'production');
+    unset($env);
 }
 
+// Location of the framework bootstrap file.
+require rtrim($paths->systemDirectory, '\\/ ') . DIRECTORY_SEPARATOR . 'bootstrap.php';
+
 // Grab our CodeIgniter
 $app = Config\Services::codeigniter();
 $app->initialize();
diff --git a/system/CodeIgniter.php b/system/CodeIgniter.php
index 85776368ed24..2bd5965bb22a 100644
--- a/system/CodeIgniter.php
+++ b/system/CodeIgniter.php
@@ -186,9 +186,6 @@ public function __construct(App $config)
      */
     public function initialize()
     {
-        // Define environment variables
-        $this->bootstrapEnvironment();
-
         // Setup Exception Handling
         Services::exceptions()->initialize();
 
@@ -584,6 +581,8 @@ protected function detectEnvironment()
      * is wrong. At the very least, they should have error reporting setup.
      *
      * @return void
+     *
+     * @deprecated 4.5.0 Moved to system/bootstrap.php.
      */
     protected function bootstrapEnvironment()
     {
diff --git a/system/bootstrap.php b/system/bootstrap.php
index be1e43c85e03..9777c7177eaa 100644
--- a/system/bootstrap.php
+++ b/system/bootstrap.php
@@ -52,6 +52,26 @@
     define('TESTPATH', realpath(rtrim($paths->testsDirectory, '\\/ ')) . DIRECTORY_SEPARATOR);
 }
 
+/**
+ * ---------------------------------------------------------------
+ * LOAD ENVIRONMENT BOOTSTRAP
+ * ---------------------------------------------------------------
+ *
+ * Load any custom boot files based upon the current environment.
+ * If no boot file exists, we shouldn't continue because something
+ * is wrong. At the very least, they should have error reporting setup.
+ */
+if (is_file(APPPATH . 'Config/Boot/' . ENVIRONMENT . '.php')) {
+    require_once APPPATH . 'Config/Boot/' . ENVIRONMENT . '.php';
+} else {
+    // @codeCoverageIgnoreStart
+    header('HTTP/1.1 503 Service Unavailable.', true, 503);
+    echo 'The application environment is not set correctly.';
+
+    exit(EXIT_ERROR); // EXIT_ERROR
+    // @codeCoverageIgnoreEnd
+}
+
 /*
  * ---------------------------------------------------------------
  * GRAB OUR CONSTANTS & COMMON