Load environment specific configuration in symfony 4 kernel

Kernel.php

<?php

namespace App;

use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\Config\Loader\LoaderInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
use Symfony\Component\Routing\RouteCollectionBuilder;

class Kernel extends BaseKernel
{
    use MicroKernelTrait;

    public const APP_LOCAL_ENVS = [
        'test',
        'dev',
        'dev_security',
    ];
    public const APP_CF_ENVS = [
        'prod',
        'cf_test',
        'cf_dev',
    ];
    private const CONFIG_EXTS = '.{php,xml,yaml,yml}';
    private const VAGRANT_USER = 'vagrant';

    /**
     * Use cache directory outside of project dir when in vagrant to not have cache go over NFS.
     */
    public function getCacheDir()
    {
        if (self::VAGRANT_USER === getenv('USER')) {
            return '/dev/shm/cache/'.$this->environment;
        }

        return $this->getProjectDir().'/var/cache/'.$this->environment;
    }

    protected function configureContainer(ContainerBuilder $container, LoaderInterface $loader)
    {
        ...

        // [standard] load regular configuration
        $loader->load($confDir.'/{packages}/*'.self::CONFIG_EXTS, 'glob');
        // [custom] load configuration overwrite for local environments
        if (\in_array($this->environment, self::APP_LOCAL_ENVS, true)) {
            $loader->load($confDir.'/{packages}/local/*'.self::CONFIG_EXTS, 'glob');
        }
        // [custom] load configuration overwrite for cloud environments
        if (\in_array($this->environment, self::APP_CF_ENVS, true)) {
            $loader->load($confDir.'/{packages}/cf/*'.self::CONFIG_EXTS, 'glob');
        }
        // [standard] load environment specific configuration
        $loader->load($confDir.'/{packages}/'.$this->environment.'/**/*'.self::CONFIG_EXTS, 'glob');

        // [custom] load regular parameters & environment group & environment specific parameters
        $loader->load($confDir.'/{parameters}/*'.self::CONFIG_EXTS, 'glob');
        if (\in_array($this->environment, self::APP_LOCAL_ENVS, true)) {
            $loader->load($confDir.'/{parameters}/local/*'.self::CONFIG_EXTS, 'glob');
        }
        if (\in_array($this->environment, self::APP_CF_ENVS, true)) {
            $loader->load($confDir.'/{parameters}/cf/*'.self::CONFIG_EXTS, 'glob');
        }
        $loader->load($confDir.'/{parameters}/'.$this->environment.'/*'.self::CONFIG_EXTS, 'glob');

        // [standard] load services & environment specific services
        $loader->load($confDir.'/{services}'.self::CONFIG_EXTS, 'glob');
        $loader->load($confDir.'/{services}/*'.self::CONFIG_EXTS, 'glob');
        $loader->load($confDir.'/{services}_'.$this->environment.self::CONFIG_EXTS, 'glob');
    }

    ...
}

list config directory

# illustration of the config/ directory structure

├── bundles.php
├── packages
│   ├── cf
│   │   └── security.yaml
│   ├── dev
│   │   ├── routing.yaml
│   │   ├── swiftmailer.yaml
│   │   └── web_profiler.yaml
│   ├── dev_security
│   │   └── dev_security.yaml
│   ├── doctrine.yaml
│   ├── framework.yaml
│   ├── jms_serializer.yaml
│   ├── rokka.yaml
│   ├── routing.yaml
│   ├── sensio_framework_extra.yaml
│   ├── swiftmailer.yaml
│   ├── test
│   │   ├── framework.yaml
│   │   ├── swiftmailer.yaml
│   │   └── web_profiler.yaml
│   ├── translation.yaml
│   ├── twig.yaml
│   └── workers.yml
├── parameters
│   ├── cf
│   │   └── cf.yaml
│   ├── cf_dev
│   │   ├── cf_dev.yaml
│   │   └── database.yaml
│   ├── cf_test
│   │   ├── cf_test.yaml
│   │   └── database.yaml
│   ├── classifications.yml
│   ├── default.yaml
│   ├── local
│   │   ├── database.yaml
│   │   └── local.yaml
│   ├── prod
│   │   ├── database.yaml
│   │   └── prod.yaml
│   ├── test
│   │   └── test.yaml
│   └── xcampaign_newsletter.yml
├── routes
│   ├── api_debug.yaml
│   ├── api.yaml
│   ├── dev
│   │   ├── twig.yaml
│   │   └── web_profiler.yaml
│   ├── dev_security
│   │   └── dev_security.yaml
│   └── user_content.yaml
├── routes.yaml
├── services
│   ├── api.product.controller.yaml
│   ├── api.product.factory.xml
│   ├── api.product.yaml
│   └── user_content.yaml
└── services_test.yaml