cri-o/vendor/github.com/opencontainers/runtime-spec/bundle.md

Filesystem Bundle

Container Format

This section defines a format for encoding a container as a filesystem bundle - a set of files organized in a certain way, and containing all the necessary data and metadata for any compliant runtime to perform all standard operations against it. See also OS X application bundles for a similar use of the term bundle.

The definition of a bundle is only concerned with how a container, and its configuration data, are stored on a local file system so that it can be consumed by a compliant runtime.

A Standard Container bundle contains all the information needed to load and run a container. This MUST include the following artifacts:

1. config.json : contains configuration data. This REQUIRED file MUST reside in the root of the bundle directory and MUST be named config.json. See config.json for more details.

2. A directory representing the root filesystem of the container. While the name of this REQUIRED directory may be arbitrary, users should consider using a conventional name, such as rootfs. This directory MUST be referenced from within the config.json file.

While these artifacts MUST all be present in a single directory on the local filesystem, that directory itself is not part of the bundle. In other words, a tar archive of a bundle will have these artifacts at the root of the archive, not nested within a top-level directory.