From memory, the early versions of Docker were basically just combining LXC with an image implementation using overlayfs. They then switched to spinning up thei

From memory, the early versions of Docker were basically just combining LXC with an image implementation using overlayfs. They then switched to spinning up their own container processes directly. Storage with LXC is just a block device, so you could roll your own using overlayfs. Probably a fair amount of work though. And in the other direction, I have used btrfs instead of overlayfs with Docker.