I think the problem might be that my host is using devicemapper. However I found this thread and this Github commit linked from it:
https://github.com/discourse/discourse_docker/commit/48f22d14f39496c8df446cbc65ee04b258c5a1a0
Yet, on my system it is not working, I get no warning or error at all from launcher.
Here is my docker info 2> /dev/null | grep 'Driver: ':
Storage Driver: devicemapper
Logging Driver: json-file
Cgroup Driver: cgroupfs