Automation/tooling support for building a local Dockerfile as a 'base image'

[baronfel]

One of our escape hatches for users that have a need to customize their base image with RUN commands (or any other functionality that we can't support) is to put just those customizations in a Dockerfile and then build and use that. It would be nice if we had a smooth, documented pathway to making that happen in the easy cases.

We might need to support:

• invoking a build of a Dockerfile
• in a given Docker build context,
• with Build Args and
• a tagged image name

in a seamless manner.

[rainersigwald]

Spitballing minimum effort approach: should we doc something like having a custom target that hooks before the container stuff that does something like docker build whatever -t mybaseimage:latest + use mybaseimage:latest as your base? There's still a missing "get the manifest info from local daemon instead of a registry" step.