Dockerfile specification

What are the challenges that we are trying to solve?
What ideas do we have for how to address these challenges?
How do these ideas break down into…
1. Already existing OCI specs?
2. A new project (CNCF or OCI)
Questions?
What pre-existing work or software can support these ideas?
Relevant OCI Issues

What are the challenges that we are trying to solve?

The best specification I’ve been able to find for Dockerfile syntax and semantics is the Dockerfile reference. However, this is a usage manual rather than a specification, so it doesn’t cover all the edge cases.

In particular:

There is no official Dockerfile grammar. The best way I’ve found to evaluate compatibility is seek bug-compatibility with Docker, which is time-consuming and error-prone. (Charliecloud has reverse engineered a grammar for ch-image that works OK for us.)
Extensibility is currently via comment hacks rather than a robust mechanism, e.g. an OPTIONS instruction (a la Python’s from __future__ statement or ignoring unknown instructions by default.

What ideas do we have for how to address these challenges?

Solid specification of the Dockerfile syntax and semantics, including a grammar. This could certainly be based on the Dockerfile reference.

It could be an opportunity to fix some of the inconsistencies, also; e.g. ARG and ENV do almost the same thing but have different syntax.

How do these ideas break down into…

Already existing OCI specs?

A new project (CNCF or OCI)

This idea suggests creating a new spec to describe the format of the Dockerfile. It should also come with conformance tests.

Questions?

What pre-existing work or software can support these ideas?

Charliecloud has made a lot of progress formalizing Dockerfile syntax and explaining where we found ambiguities.