## apps/frontend/config/factories.yml

all:
  controller:
    class: mySfFrontWebController


## apps/frontend/config/app.yml

all:
  database_not_connected:
    module:       main
    action:       notconnected


## apps/frontend/config/frontendConfiguration.class.php

class frontendConfiguration extends sfApplicationConfiguration
{
  public function configure()
  {
    $this->dispatcher->connect('doctrine.configure_connection', array($this, 'listenToAddCheckDatabaseConnection'));
  }

  public function listenToAddCheckDatabaseConnection(sfEvent $event)
  {
    $actions = $event->getSubject();
    sfConfig::set('sf_database_is_connected', $actions->getCurrentConnection()->isConnected());
  }

}


## lib/controller/mySfFrontWebController.class.php

class mySfFrontWebController extends sfFrontWebController
{
  public function dispatch()
  {
    if (!sfConfig::get('sf_database_is_connected', true))
    {
      $request    = $this->context->getRequest();
      $moduleName = $request->getParameter('module');
      $actionName = $request->getParameter('action');

      if ((!$module = sfConfig::get('app_database_not_connected_module')) ||
      (!$action = sfConfig::get('app_database_not_connected_action')))
      {
        throw new sfConfigurationException('Missing parameters app_database_not_connected_module and/or app_database_not_connected_action in app.yml');
      }
      else
      {
        if (($moduleName != $module) && ($actionName != $action))
        {
          $this->forward($module, $action);
          exit;
        }
      }
    }
    parent::dispatch();
  }
}