Thanks for poking me. @jdstrand
@elopio Yes, the project instruction is a bit out of date and needs some updates.
Basically, I started this simple experimental project prior to 17.06.0-ce-1 release which is the one you now can find at stable channel of latest and 17.06 track in store. It aims to demonstrate how to build a dockerzied app through the content-interface shared by the docker snap. So people could just simply ship a piece of Dockerfile or a docker-compose.yml into their snap package and invoke docker from a dockerized snap sandbox to build images and run a container. With the content shared from docker snap, we can achieve great results with extremely small package size and people won't need to include docker binary in their final snap package. Another benefit of this is that it allows people using snap as a delivery mechanism to update Dockerfile or docker-compose.yml. It's small and cheap.
As Jamie commented, the downside of this approach is that docker-support gives people high-privilege access to OS. So it's highly recommended not to use this method in untrusted apps due to security escape. This approach is a reasonable and effective compromise for trusted apps in a brand store.
Meanwhile, I'd like to mention that a dockerized app probably won't work if it runs as a daemon according to my findings. It seems like a bug in snapd.
I'll update the instruction and limitation of this approach in the sample repo.
Thanks for your feedbacks!