Mysql container and php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution

Hello everyone,

I’m a bit stumped on this one and I hope to get help from you guys.

I have a working docker-compose file on my home box (Linux Mint 18 Sarah): apache, php, phpmyadmin and mysql work fine together. My Symfony based project works fine.
The same docker-compose.yml file on my work box (Ubuntu 18.04) yields the dreaded php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution.

Php container does not seem to be able to resolve mysql (service name) in the DB connection:

DATABASE_URL=mysql://sf4:sf4@mysql:3306/backoffice

I get a different error message if I change it to localhost

DATABASE_URL=mysql://sf4:sf4@localhost:3306/backoffice
An exception occurred in driver: SQLSTATE[HY000] [2002] No such file or directory

I am using the same network on both computers.

Docker-compose.yml is as follows:

version: '3'
services:
    apache:
        build: .docker/apache
        container_name: sf4_apache
        ports:
          - 80:80
        expose:
            - 80
            - 9000 # x-debug
        volumes:
          - .docker/config/vhosts:/etc/apache2/sites-enabled
          - .:/var/www/back-office
        depends_on:
          - php

    mysql:
        image: mysql:5.7.23
        container_name: sf4_mysql
        volumes:
            - .docker/data/db:/var/lib/mysql
        environment:
            MYSQL_ROOT_PASSWORD: root
            MYSQL_DATABASE: backoffice
            MYSQL_USER: sf4
            MYSQL_PASSWORD: sf4

    php:
        build: .docker/php
        container_name: sf4_php
        volumes:
          - .:/var/www/back-office
        environment:
          - maildev_host=sf4_maildev
        depends_on:
          - maildev
          - mysql

    phpmyadmin:
        image: phpmyadmin/phpmyadmin
        container_name: sf4_phpmyadmin
        depends_on:
            - mysql
        ports:
            - 8080:80
        links:
            - mysql
        environment:
            PMA_HOSTS: mysql

    maildev:
        image: djfarrelly/maildev
        container_name: sf4_maildev
        ports:
          - 8001:80

Thanks!