Symfony_2_local_config_file.php

/**
 * Enhance your Symfony 2 kernel to check for a local configuration file.
 */

public function registerContainerConfiguration()
{
    $loader = new ContainerLoader($this->getBundleDirs());
    $configuration = $loader->load(__DIR__.'/config/config_'.$this->getEnvironment().'.yml');

    // check for a local configuration file
    if (file_exists($file = __DIR__.'/config/config_local.yml')) {
        $configuration->merge($loader->load($file));
    }

    return $configuration;
}