I’m not sure it is aufs. We restored a good backup to another VM and have the service working there. /var/lib/docker/aufs doesn’t exist on that VM. The storage driver on that VM is “devicemapper”. On the copy of the broken production VM (which has other services working on it) I’m trying to setup up Discourse and Docker on a partition with more disk space. That partition was already there and is in use but, I just discovered, is XFS and does not have d_type set. Strangely, without /etc/docker/daemon.json on the working VM the storage driver is devicemapper by default and on the “broken” VM copy it is overlay. I guess this is because docker knows it’s being written to XFS.
This allowed us to install the container with the base discourse. After we added the socket template we got an error related to Nginx starting up in the container but quickly fixed that. We then restored the Discourse backup and now know how to resurrect the site in production. Thanks for your help.