How to create mass 301 redirects with PHP in Nginx server without using a WP plugin

Question

Seems the easiest way to do it is via PHP without changing any Nginx server config by adding this at the start of the wp-config.php file:

// Trailing slashes matters here so /old1 is different from /old1/
$redirect_targets = array(
  '/old-url' => '/new-url',
  '/old-url2' => '/new-url2',
  '/old-url3' => '/new-url3',
);

// Added a way not to accidentally break wp-cli
if ( (isset($redirect_targets[ $_SERVER['REQUEST_URI'] ] ) ) && (php_sapi_name() != "cli") ) {
  header('HTTP/1.0 301 Moved Permanently');
  header('Location: https://'. $_SERVER['HTTP_HOST'] . $redirect_targets[ $_SERVER['REQUEST_URI'] ]);

  exit();
}