SWhat container runtime/network setup are you running? This seems like an issue with container setup (cgroups and what I assume is a network namespace issue)
SAlso, if you’re running docker, take a look at the dockerd logs…I suspect you’ll see errors about setting up cgroups or your network namespace. I’d confirm both containers are in the same network ns or have port forwarding enabled. Can inspect the ns of each container by determining the PID of the windmill and Postgres container and inspecting
SNot entirely sure what distro of Linux your NAS is running, it’s a little strange it can’t find the CFS tho 
SWell if your windmill container isn’t running in the root namespace, I don’t think it’d be able to connect to the container.
SNo root network namespace, slightly different
SMind pasting your docker-compose config?
SSo I think swap the port back to 5432 (it won’t conflict as it’s in a different namespace)
SDon’t add the expose as that will conflict