namespace SymfonyComponentHttpKernel;

...


/**
 * The Kernel is the heart of the Symfony system.
 *
 * It manages an environment made of bundles.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 */
abstract class Kernel implements KernelInterface, TerminableInterface
{
    ...
        /**
     * Initializes the service container.
     *
     * The cached version of the service container is used when fresh, otherwise the
     * container is built.
     */
    protected function initializeContainer()
    {
        $class = $this->getContainerClass();
        // !!!!!! cache config object construction
        $cache = new ConfigCache($this->getCacheDir().'/'.$class.'.php', $this->debug);
        $fresh = true;
        if (!$cache->isFresh()) {
            $container = $this->buildContainer();
            $container->compile();
            $this->dumpContainer($cache, $container, $class, $this->getContainerBaseClass());

            $fresh = false;
        }

        require_once $cache->getPath();

        $this->container = new $class();
        $this->container->set('kernel', $this);

        if (!$fresh && $this->container->has('cache_warmer')) {
            $this->container->get('cache_warmer')->warmUp($this->container->getParameter('kernel.cache_dir'));
        }
    }
}

-home

 --symfony_app

 --custom_cache_directory

public function getCacheDir()
{
    return dirname(__DIR__).'/../custom_cache_directory/cache/'.$this->getEnvironment();
}