67 lines
3.9 KiB
Markdown
67 lines
3.9 KiB
Markdown
# Open Container Initiative
|
|
## Image Format Specification
|
|
|
|
This specification defines an OCI Image, consisting of a [manifest](manifest.md), an [image index](image-index.md) (optional), a set of [filesystem layers](layer.md), and a [configuration](config.md).
|
|
|
|
The goal of this specification is to enable the creation of interoperable tools for building, transporting, and preparing a container image to run.
|
|
|
|
### Table of Contents
|
|
|
|
- [Introduction](spec.md)
|
|
- [Notational Conventions](#notational-conventions)
|
|
- [Overview](#overview)
|
|
- [Understanding the Specification](#understanding-the-specification)
|
|
- [Media Types](media-types.md)
|
|
- [Content Descriptors](descriptor.md)
|
|
- [Image Layout](image-layout.md)
|
|
- [Image Manifest](manifest.md)
|
|
- [Image Index](image-index.md)
|
|
- [Filesystem Layers](layer.md)
|
|
- [Image Configuration](config.md)
|
|
- [Annotations](annotations.md)
|
|
- [Considerations](considerations.md)
|
|
- [Extensibility](considerations.md#extensibility)
|
|
- [Canonicalization](considerations.md#canonicalization)
|
|
|
|
## Notational Conventions
|
|
|
|
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC 2119](http://tools.ietf.org/html/rfc2119) (Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997).
|
|
|
|
The key words "unspecified", "undefined", and "implementation-defined" are to be interpreted as described in the [rationale for the C99 standard][c99-unspecified].
|
|
|
|
An implementation is not compliant if it fails to satisfy one or more of the MUST, MUST NOT, REQUIRED, SHALL, or SHALL NOT requirements for the protocols it implements.
|
|
An implementation is compliant if it satisfies all the MUST, MUST NOT, REQUIRED, SHALL, and SHALL NOT requirements for the protocols it implements.
|
|
|
|
## Overview
|
|
|
|
At a high level the image manifest contains metadata about the contents and dependencies of the image including the content-addressable identity of one or more [filesystem layer changeset](layer.md) archives that will be unpacked to make up the final runnable filesystem.
|
|
The image configuration includes information such as application arguments, environments, etc.
|
|
The image index is a higher-level manifest which points to a list of manifests and descriptors.
|
|
Typically, these manifests may provide different implementations of the image, possibly varying by platform or other attributes.
|
|
|
|
|
|
|
|
Once built the OCI Image can then be discovered by name, downloaded, verified by hash, trusted through a signature, and unpacked into an [OCI Runtime Bundle](https://github.com/opencontainers/runtime-spec/blob/master/bundle.md).
|
|
|
|
|
|
|
|
### Understanding the Specification
|
|
|
|
The [OCI Image Media Types](media-types.md) document is a starting point to understanding the overall structure of the specification.
|
|
|
|
The high-level components of the spec include:
|
|
|
|
* [Image Manifest](manifest.md) - a document describing the components that make up a container image
|
|
* [Image Index](image-index.md) - an annotated index of image manifests
|
|
* [Image Layout](image-layout.md) - a filesystem layout representing the contents of an image
|
|
* [Filesystem Layer](layer.md) - a changeset that describes a container's filesystem
|
|
* [Image Configuration](config.md) - a document determining layer ordering and configuration of the image suitable for translation into a [runtime bundle][runtime-spec]
|
|
* [Descriptor](descriptor.md) - a reference that describes the type, metadata and content address of referenced content
|
|
|
|
Future versions of this specification may include the following OPTIONAL features:
|
|
|
|
* Signatures that are based on signing image content address
|
|
* Naming that is federated based on DNS and can be delegated
|
|
|
|
[c99-unspecified]: http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf#page=18
|
|
[runtime-spec]: https://github.com/opencontainers/runtime-spec
|