You should map your /config to a known folder on your NAS. I do it like this on my QNAP:
volumes:
- /share/container/service:/config
and I have a shared folder named container:

You should map your /config to a known folder on your NAS. I do it like this on my QNAP:
volumes:
- /share/container/service:/config
and I have a shared folder named container:
