Our docker compose role is configured via ansible variables in a way
that overwrites each other if it is activated twice with different
variable assignments (unless e.g. a role that just installs more
packages).
To prevent misuse of the role, the allow_duplicates key of the role
meta is set to false. This should make ansible complain if the role
is included twice for a single host.
This is needed for situations, where one wants to use a vendor-provided
compose file and configure it using environment variables.
Like for example:
https://github.com/zammad/zammad-docker-compose