Load configuration files depending on host in Symfony

AcmeExtension.php

// src/AcmeBundle/DependencyInjection/AcmeExtension.php

<?php

namespace AcmeBundle\DependencyInjection;

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

class AcmeExtension extends Extension
{
    public function load(array $configs, ContainerBuilder $container)
    {
        $configuration = new Configuration();
        $config = $this->processConfiguration($configuration, $configs);
        $rootdir = $container->getParameter('kernel.root_dir');

        // Load the bundle's services.yml
        $loader = new Loader\YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
        $loader->load('services.yml');

        // Load parameters depending on current host
        $paramLoader = new Loader\YamlFileLoader($container, new FileLocator($rootdir.'/config')); // Access the root config directory
        $parameters = sprintf('parameters_%s.yml', $container->getParameter('router.request_context.host'));

        if (!file_exists($rootdir.'/config/'.$parameters)) {
            $parameters = 'parameters.yml'; // Default
        }

        $paramLoader->load($parameters); 
    }
}

Configuration.php

// src/AcmeBundle/DependencyInjection/Configuration.php

<?php

namespace AcmeBundle\DependencyInjection;

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

class Configuration implements ConfigurationInterface
{
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('acme');

        return $treeBuilder;
    }
}

If router.request_context.host is always equal to localhost, use $_SERVER['SERVER_NAME'] instead.