Symfony2 Custom Configuration

AppCoreExtension.php

<?php
/**
 * application/src/App/CoreBundle/DependencyInjection/AppCoreExtension.php
 * 
*/

namespace App\CoreBundle\DependencyInjection;

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\HttpKernel\DependencyInjection\Extension;
use Symfony\Component\DependencyInjection\Loader;

/**
 * This is the class that loads and manages your bundle configuration
 *
 * To learn more see {@link http://symfony.com/doc/current/cookbook/bundles/extension.html}
 */
class AppCoreExtension extends Extension
{
    /**
     * {@inheritDoc}
     */
    public function load(array $configs, ContainerBuilder $container)
    {
        $configuration = new Configuration();
        $config = $this->processConfiguration($configuration, $configs);

        $loader = new Loader\YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
        $loader->load('services.yml');
        
        if (!isset($config['amazon_s3']['aws_key'])) {
        	throw new \InvalidArgumentException('The option "app.amazon_s3.aws_key" must be set.');
        }
        $container->setParameter('app.amazon_s3.aws_key', $config['amazon_s3']['aws_key']);
        
        if (!isset($config['amazon_s3']['aws_secret_key'])) {
        	throw new \InvalidArgumentException('The option "app.amazon_s3.aws_secret_key" must be set.');
        }
        $container->setParameter('app.amazon_s3.aws_secret_key', $config['amazon_s3']['aws_secret_key']);
        
        if (!isset($config['test_variable'])) {
          throw new \InvalidArgumentException('The option "app.test_variable" must be set.');
        }
        $container->setParameter('app.test_variable', $config['test_variable']);
    }
}

AppKernel.php

<?php
/**
 * application/app/AppKernel.php
 * 
*/

use Symfony\Component\HttpKernel\Kernel;
use Symfony\Component\Config\Loader\LoaderInterface;

class AppKernel extends Kernel
{
    public function registerBundles()
    {
        $bundles = array(
            new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
            new Symfony\Bundle\SecurityBundle\SecurityBundle(),
            new Symfony\Bundle\TwigBundle\TwigBundle(),
            new Symfony\Bundle\MonologBundle\MonologBundle(),
            new Symfony\Bundle\SwiftmailerBundle\SwiftmailerBundle(),
            new Symfony\Bundle\AsseticBundle\AsseticBundle(),
            new Doctrine\Bundle\DoctrineBundle\DoctrineBundle(),
            new Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle(),
            new FOS\ElasticaBundle\FOSElasticaBundle(),
            new FOS\JsRoutingBundle\FOSJsRoutingBundle(),
            new WhiteOctober\PagerfantaBundle\WhiteOctoberPagerfantaBundle(),
            new Doctrine\Bundle\FixturesBundle\DoctrineFixturesBundle(),
            new App\CoreBundle\AppCoreBundle(),
            new JMS\SerializerBundle\JMSSerializerBundle(),
            new HWI\Bundle\OAuthBundle\HWIOAuthBundle(),
            new Liip\ThemeBundle\LiipThemeBundle(),
            new Knp\Bundle\MenuBundle\KnpMenuBundle(),
            new FOS\RestBundle\FOSRestBundle(),
            new Nelmio\ApiDocBundle\NelmioApiDocBundle(),
            new Lsw\MemcacheBundle\LswMemcacheBundle(),
            new Exercise\HTMLPurifierBundle\ExerciseHTMLPurifierBundle(),
            new Misd\GuzzleBundle\MisdGuzzleBundle(),
            new Gregwar\CaptchaBundle\GregwarCaptchaBundle(),
        );

        return $bundles;
    }

    public function registerContainerConfiguration(LoaderInterface $loader)
    {
        $loader->load(__DIR__.'/config/config_'.$this->getEnvironment().'.yml');

        $envParameters = $this->getEnvParameters();
        $loader->load(function($container) use($envParameters) {
            $container->getParameterBag()->add($envParameters);
        });
    }

    public function getCacheDir()
    {
        return '/tmp/application/cache/'.$this->environment;
    }

    public function getLogDir()
    {
        return '/tmp/application/logs';
    }
}

config.yml

# application/app/config/config.yml

app_core:
    amazon_s3:
        aws_key:        "%amazon_aws_key%"
        aws_secret_key: "%amazon_aws_secret_key%"
    test_variable: "%test.variable%"

Configuration.php

<?php
/**
 * application/src/App/CoreBundle/DependencyInjection/Configuration.php
 * 
*/

namespace App\CoreBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

/**
 * This is the class that validates and merges configuration from your app/config files
 *
 * To learn more see {@link http://symfony.com/doc/current/cookbook/bundles/extension.html#cookbook-bundles-extension-config-class}
 */
class Configuration implements ConfigurationInterface {

    /**
     * {@inheritDoc}
     */
    public function getConfigTreeBuilder() {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('app_core');

        $rootNode
                ->children()
                    ->arrayNode('amazon_s3')
                        ->children()
                            ->scalarNode('aws_key')->end()
                            ->scalarNode('aws_secret_key')->end()
                        ->end()
                    ->end()
                    ->scalarNode('test_variable')->end()
                ->end();

        // Here you should define the parameters that are allowed to
        // configure your bundle. See the documentation linked above for
        // more information on that topic.

        return $treeBuilder;
    }

}