WordPress via Docker behind proxy - cURL error 7, no route to host

I'm trying to set up a WordPress site via Docker and I'm behind a proxy 193.56.47.8:8080.

When I do a check with the Health Check plugin, here are the errors I have:

REST API availability: The REST API request failed due to an error. Error encountered: (0) cURL error 7: Failed to connect to 172.24.155.18 port 80: No route to host

I've deleted all other plugins and themes and made the proxy settings in the wp-config.php file:

define('WP_PROXY_HOST', '193.56.47.8');
define('WP_PROXY_PORT', '8080');
define('WP_PROXY_USERNAME', 'xxxxxxxxxx');
define('WP_PROXY_PASSWORD', 'xxxxxxxxxx');
define('WP_PROXY_BYPASS_HOSTS', 'localhost, *.wordpress.org');

Here is my docker-compose.yml:

wordpress:
    image: wordpress
    links:
     - mariadb:mysql
    environment:
     - WORDPRESS_DB_PASSWORD=password
    ports:
     - "172.24.155.18:80:80"
    volumes:
     - ./code:/code
     - ./html:/var/www/html
mariadb:
    image: mariadb
    environment:
     - MYSQL_ROOT_PASSWORD=password
     - MYSQL_DATABASE=wordpress
    volumes:
     - ./database:/var/lib/mysql

The website is running but didn't I miss any additional settings?

-centOS 7