OK - I found the solution.
I edit the docker-compose.yml file and add a aliases flag for the cms-db service. Now the cms-db Container is linked in the cms-web Container again with “mysql” and everything is working as before.
And the reason it took so long for me to find the solution was: I didn’t understand how to access the default network, because the examples I found always mention a concrete docker network. So I missed the keyword “default” and my tries failed.
cms-db:
image: mysql:5.7
volumes:
- "./shared/db:/var/lib/mysql:Z"
environment:
- MYSQL_DATABASE=cms
- MYSQL_USER=cms
- MYSQL_RANDOM_ROOT_PASSWORD=yes
mem_limit: 1g
env_file: config.env
restart: always
networks:
default:
aliases:
- mysql