1、下载镜像的manifest 2、从manifest中获取镜像的imageid,若imageid在本地已存在,则结束 3、从manifest中获取各个layer的digest,根据digest查找该layer是否存在本地,若存在则无需下载该layer;若不存在,则从registry下载该layer 4、根据本地的后端存储更新相应的文件
/v2/{repository}/manifests/{tag}
{
"schemaVersion": 2,
"mediaType": "application/vnd.docker.distribution.manifest.v2+json",
"config": {
"mediaType": "application/vnd.docker.container.image.v1+json",
"size": 3017,
"digest": "sha256:c6c14b3960bdf9f5c50b672ff566f3dabd3e450b54ae5496f326898513362c98"
},
"layers": [
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 2310286,
"digest": "sha256:e110a4a1794126ef308a49f2d65785af2f25538f06700721aad8283b81fdfa58"
},
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 614066,
"digest": "sha256:2ee5ed28ffa762104505295c3c256c52a87fe8af0114b9e0198e9036495e10b8"
},
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 6726616,
"digest": "sha256:d1562c23a8aa4913a2fc720a3c478121f45d26597b58bbf9a29238276ca420a7"
},
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 370,
"digest": "sha256:06ba8e23299fcf9dd9efb3c5acd4c9d03badac5392953001c75d38197113a63a"
},
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 215,
"digest": "sha256:802d2a9c64e8f556e510b4fe6c5378b9d49d8335a766d156ef21c7aeac64c9d6"
}
]
}
在得到镜像的manifest之后,根据layers中layer的digest,去registry的API中下载相应的layer。关于layer的API有如下几个:
HEAD /v2/{repository}/blobs/{digest}
GET /v2/{repository}/blobs/{digest}