OCI Image Media Types

Image Media Types简介

application/vnd.oci.descriptor.v1+json Content Descriptor
application/vnd.oci.layout.header.v1+json OCI Layout
application/vnd.oci.image.index.v1+json Image Index
application/vnd.oci.image.manifest.v1+json Image Manifest
application/vnd.oci.image.config.v1+json Image Config
application/vnd.oci.image.layer.v1.tar “Layer”, as a tar archive
application/vnd.oci.image.layer.v1.tar+gzip “Layer”, as a tar archive compressed with gzip
application/vnd.oci.image.layer.nondistributable.v1.tar “Layer”, as a tar archive with distribution restrictions
application/vnd.oci.image.layer.nondistributable.v1.tar+gzip “Layer”, as a tar archive with distribution restrictions compressed with gzip

各Media Types之间关系

以上各个Image Type之间的关系如下图所示：

Content Descriptor

概念

An OCI Image包含包含多个组件。
组件之间的引用格式为：content descriptor。
一个Content Descriptor表示目标content。
Content Descriptor包含至少三部分：type of content，digest of content，byte-size of the raw content。
Descriptors应该嵌入在其他的格式（Image Types）中，用来引用外部的content。
其他的格式（Image Types）应该使用Descriptors引用外部content。
属性

三个必需的属性：
mediaType
digest
size 两个可选的属性：
urls
annotations
例子

```json { “mediaType”: “application/vnd.oci.image.manifest.v1+json”, “size”: 7682, “digest”: “sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270” }

{ “mediaType”: “application/vnd.oci.image.manifest.v1+json”, “size”: 7682, “digest”: “sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270”, “urls”: [ “https://example.com/example-manifest” ] }

## Image Layout
### 三部分
* blobs
* oci-layout
* index.json
### BLOBS
* `blobs`的子目录为各个hash算法。比如sha256，sha512。
* `blobs/<alg>/<encoded>的内容必须和content descriptor中的`digest <alg>:<encoded>`相匹配。比如：blobs/sha256/da39a3ee5e6b4b0d3255bfef95601890afd80709的内容和descriptor中的digest sha256:da39a3ee5e6b4b0d3255bfef95601890afd80709完全匹配。
### OCI-LAYOUT
Image Type of OCI-Layout是：`application/vnd.oci.layout.header.v1+json`

```json
{
    "imageLayoutVersion": "1.0.0"
}

INDEX.JSON

该文件是Image Layout中的references和descriptors中的入口。该文件的格式为application/vnd.oci.image.index.v1+json

OCI Image Index Specification

application/vnd.oci.image.index.v1+json。

Image Index指向具体的Image Manifests，是一个higher-levle manifest。

属性

schemaVersion： 2
mediaType
manifests
- mediaType：一般由2个选择：
  1. application/vnd.oci.image.manifest.v1+json
  2. application/vnd.oci.image.index.v1+json (nested index)
- platform
  - architecture
  - os
  - os.version
  - os.features：字符串数组
  - variant
  - features

annotations

例子

{
"schemaVersion": 2,
"manifests": [
  {
    "mediaType": "application/vnd.oci.image.manifest.v1+json",
    "size": 7143,
    "digest": "sha256:e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f",
    "platform": {
      "architecture": "ppc64le",
      "os": "linux"
    }
  },
  {
    "mediaType": "application/vnd.oci.image.manifest.v1+json",
    "size": 7682,
    "digest": "sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270",
    "platform": {
      "architecture": "amd64",
      "os": "linux"
    }
  }
],
"annotations": {
  "com.example.key1": "value1",
  "com.example.key2": "value2"
}
}

OCI Image Manifest Specification

application/vnd.oci.image.manifest.v1+json。

概念

Image Manifest：描述了一个针对具体arch和os的container image，包括两大部分：一个configuration和多个layers。

configuration由application/vnd.oci.image.config.v1+json描述
layers的格式较多，包括：
- application/vnd.oci.image.layer.v1.tar
- application/vnd.oci.image.layer.v1.tar+gzip
- application/vnd.oci.image.layer.nondistributable.v1.tar
- application/vnd.oci.image.layer.nondistributable.v1.tar+gzip

属性

schemaVersion
mediaType
config
- mediaType
- size
- digest
layers [ { * mediaType * size * digest } ]

annotations

例子

{
"schemaVersion": 2,
"config": {
  "mediaType": "application/vnd.oci.image.config.v1+json",
  "size": 7023,
  "digest": "sha256:b5b2b2c507a0944348e0303114d8d93aaaa081732b86451d9bce1f432a537bc7"
},
"layers": [
  {
    "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
    "size": 32654,
    "digest": "sha256:9834876dcfb05cb167a5c24953eba58c4ac89b1adf57f28f2f9d09af107ee8f0"
  },
  {
    "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
    "size": 16724,
    "digest": "sha256:3c3a4604a545cdc127456d94e421cd355bca5b528f4a9c1905b15da2eb4a4c6b"
  },
  {
    "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
    "size": 73109,
    "digest": "sha256:ec4b8955958665577945c89419d1af06b5f7636b4ac3da7f12184802ad867736"
  }
],
"annotations": {
  "com.example.key1": "value1",
  "com.example.key2": "value2"
}
}

OCI Image Configuration

application/vnd.oci.image.config.v1+json。

An OCI Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime.

ImageID

Each image’s ID is given by the SHA256 hash of its configuration JSON.

Layers Types

application/vnd.oci.image.layer.v1.tar
application/vnd.oci.image.layer.v1.tar+gzip
application/vnd.oci.image.layer.nondistributable.v1.tar
application/vnd.oci.image.layer.nondistributable.v1.tar+gzip

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