Ok, meanwhile I know much more of the problem.
It is the same issue described here:
But I ran Version 2.3.x and after I did this mysql update:
I got the same problem as before. The cms-web Container can’t connect the cms-db Container with the alias “mysql” but over the IP and even with “cms-db” the mysql connection from cms-web to cms-db work fine.
For me it looks like the docker-compose “links” flag don’t work. May this is the reason?
“The --link flag is a legacy feature of Docker. It may eventually be removed.”