LXC running docker fails to start after upgrade from 6.4 to 7.0

I was doing a test upgrade today on on server, followed the upgrade guide. I had a number of turnkey core 16.0 LXC's running docker, and after upgrade these failed to start docker. I eventually chased the first issue down to "overlay" not being available, so I added that to /etc/modules-load.d/modules.conf. and rebooted. Then I ran into the second issue with cgroups:

WARN[2021-07-06T14:42:58.934309464-05:00] Your kernel does not support cgroup memory limit...

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