One approach I've seen rather successfully is to have a container that just contains the files to deploy, and another one for the runtime. You only need to update the runtime container ~ once a week or so (to get OS security updates), and the files container is literally just a COPY command to a volume.

I've only seen that in one place, ever. Most people just do the insane 40 minute docker build -- though I've also seen some that take over 4 hours...