概述

OCI指的是Open Container Initiative即开放容器计划。OCI 制定的主要标准有三个分别是 runtime-spec 、image-spec 和 distribution-spec 这三个标准分别定义了容器运行时，容器镜像还有分发的规范.

oci-image

从pull流程看镜像

client: image_name:tag , server: -> manifest
client: manifest -> image_id(config.digest) , server: -> image_config
clinet: image_config -> layer diff_ids , server: manifest_id -> layer
client: layer -> unzip -> diff match diff_ids

从id讲起

manifest.config.digest: registry唯一标识一个image
diff_ids: 每一层对应的tar(未压缩)对应的id
layer digest(manifest.layers.digest): layer存储在registry中的id，对应压缩后的tar的哈希值

那么，结合examples，整个id生成的链条就清晰了：

image的原初形象是一个文件系统目录，里面有一堆文件，以overlayfs格式组织，任何一次修改都会产生一层layer；
每层layer打包为一个tar，就可以求出他的哈希值，称为diff_ids，保存在image-config中；
一个image由各层layer的tar.zip加上image-config组成，然后对image-config求哈希值得到image-id，是为了保证image和layer不被篡改；因为一旦篡改，image-config的diff_ids就会改变，image-config的哈希就会改变，image-id就会改变；

examples

manifest

GET /v2/<name>/manifests/<reference>
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "digest": "sha256:b5b2b2c507a0944348e0303114d8d93aaaa081732b86451d9bce1f432a537bc7",
    "size": 7023
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:9834876dcfb05cb167a5c24953eba58c4ac89b1adf57f28f2f9d09af107ee8f0",
      "size": 32654
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:3c3a4604a545cdc127456d94e421cd355bca5b528f4a9c1905b15da2eb4a4c6b",
      "size": 16724
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:ec4b8955958665577945c89419d1af06b5f7636b4ac3da7f12184802ad867736",
      "size": 73109
    }
  ],
  "subject": {
    "mediaType": "application/vnd.oci.image.manifest.v1+json",
    "digest": "sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270",
    "size": 7682
  },
  "annotations": {
    "com.example.key1": "value1",
    "com.example.key2": "value2"
  }
}

image config

{
    "created": "2015-10-31T22:22:56.015925234Z",
    "author": "Alyssa P. Hacker <alyspdev@example.com>",
    "architecture": "amd64",
    "os": "linux",
    "config": {
        "User": "alice",
        "ExposedPorts": {
            "8080/tcp": {}
        },
        "Env": [
            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
            "FOO=oci_is_a",
            "BAR=well_written_spec"
        ],
        "Entrypoint": [
            "/bin/my-app-binary"
        ],
        "Cmd": [
            "--foreground",
            "--config",
            "/etc/my-app.d/default.cfg"
        ],
        "Volumes": {
            "/var/job-result-data": {},
            "/var/log/my-app-logs": {}
        },
        "WorkingDir": "/home/alice",
        "Labels": {
            "com.example.project.git.url": "https://example.com/project.git",
            "com.example.project.git.commit": "45a939b2999782a3f005621a8d0f29aa387e1d6b"
        }
    },
    "rootfs": {
      "diff_ids": [
        "sha256:c6f988f4874bb0add23a778f753c65efe992244e148a1d2ec2a8b664fb66bbd1",
        "sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef"
      ],
      "type": "layers"
    },
    "history": [
      {
        "created": "2015-10-31T22:22:54.690851953Z",
        "created_by": "/bin/sh -c #(nop) ADD file:a3bc1e842b69636f9df5256c49c5374fb4eef1e281fe3f282c65fb853ee171c5 in /"
      },
      {
        "created": "2015-10-31T22:22:55.613815829Z",
        "created_by": "/bin/sh -c #(nop) CMD [\"sh\"]",
        "empty_layer": true
      }
    ]
}

index(多架构)

{
  "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"
  }
}