The problem about index: REQUIRED or OPTIONAL?

[Zheaoli]

I have noticed that we describe the index as an optional in here

image-spec/spec.md

Line 5 in f5f8701

This specification defines an OCI Image, consisting of an [image manifest](manifest.md), an [image index](image-index.md) (optional), a set of [filesystem layers](layer.md), and a [configuration](config.md).

But we describe that the index.json is REQUIRED in here

image-spec/image-layout.md

Line 28 in f5f8701

- It MUST exist

Is there a conflict description?

FYI I have noticed that the OPTIONAL is added in this PR https://github.com/opencontainers/image-spec/pull/455/files

cc @coolljt0725

[michaelb990]

The image-layout.md describes the way to organize an image as a directory structure. The index.json file described in the Image Layout spec is specific to the on-disk representation of an image and isn't the same as an "image index" described in the image-index.md file. Perhaps it's worth disambiguating the index.json file in the image-layout.md specification.

[sudo-bmitch]

I believe this is a duplicate of #1175. I'm curious if there's something outside of OCI happening that is causing the sudden attention on this?