Is that possible to get image ID from Docker Registry V2?

问题

When an image has been pushed to registry V2, does the image ID will be pushed to registry as well? Is that possible to get image ID for a certain repository from V2 registry?

回答1:

If the image was pushed with Docker Client 1.10 or above, you can obtain the image ID from the registry with

GET /v2/<image>/manifests/<tag> 

Your request must include the header

Accept: application/vnd.docker.distribution.manifest.v2+json

In the response, the image ID will be in the Content-Docker-Digest Response header.

回答2:

From my research, you can obtain the image ID from the registry(2.3.0+) with

curl -H 'Accept: application/vnd.docker.distribution.manifest.v2+json' http://$server/v2/$repo/manifests/$tag

and the config.digest field in the response represents imageID,that what you want!

for example

refers: https://duyanghao.github.io/docker-registry-pull-manifest-v2/

回答3:

As best I can tell, they are not stored in any api accessible location:

bash$ docker run -d -p 5000:5000 --restart=always --name registry registry:2
Unable to find image 'registry:2' locally
2: Pulling from library/registry
...
bash$ docker tag busybox localhost:5000/busybox
bash$ docker push localhost:5000/busybox
The push refers to a repository [localhost:5000/busybox]
5f70bf18a086: Pushed 
...
bash$ curl http://localhost:5000/v2/busybox/tags/list
{"name":"busybox","tags":["latest"]}
bash$ curl http://localhost:5000/v2/busybox/manifests/latest
{
   "schemaVersion": 1,
   "name": "busybox",
   "tag": "latest",
   "architecture": "amd64",
   "fsLayers": [
      {
         "blobSum": "sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4"
      },
      {
         "blobSum": "sha256:385e281300cc6d88bdd155e0931fbdfbb1801c2b0265340a40481ee2b733ae66"
      }
   ],
   "history": [
      {
         "v1Compatibility": "{\"architecture\":\"amd64\",\"config\":{\"Hostname\":\"156e10b83429\",\"Domainname\":\"\",\"User\":\"\",\"AttachStdin\":false,\"AttachStdout\":false,\"AttachStderr\":false,\"Tty\":false,\"OpenStdin\":false,\"StdinOnce\":false,\"Env\":null,\"Cmd\":[\"sh\"],\"Image\":\"56ed16bd6310cca65920c653a9bb22de6b235990dcaa1742ff839867aed730e5\",\"Volumes\":null,\"WorkingDir\":\"\",\"Entrypoint\":null,\"OnBuild\":null,\"Labels\":{}},\"container\":\"5f8098ec29947b5bea80483cd3275008911ce87438fed628e34ec0c522665510\",\"container_config\":{\"Hostname\":\"156e10b83429\",\"Domainname\":\"\",\"User\":\"\",\"AttachStdin\":false,\"AttachStdout\":false,\"AttachStderr\":false,\"Tty\":false,\"OpenStdin\":false,\"StdinOnce\":false,\"Env\":null,\"Cmd\":[\"/bin/sh\",\"-c\",\"#(nop) CMD [\\\"sh\\\"]\"],\"Image\":\"56ed16bd6310cca65920c653a9bb22de6b235990dcaa1742ff839867aed730e5\",\"Volumes\":null,\"WorkingDir\":\"\",\"Entrypoint\":null,\"OnBuild\":null,\"Labels\":{}},\"created\":\"2016-03-18T18:22:48.810791943Z\",\"docker_version\":\"1.9.1\",\"id\":\"437595becdebaaaf3a4fc3db02c59a980f955dee825c153308c670610bb694e1\",\"os\":\"linux\",\"parent\":\"920777304d1d5e337bc59877253e946f224df5aae64c72538672eb74637b3c9e\"}"
      },
      {
         "v1Compatibility": "{\"id\":\"920777304d1d5e337bc59877253e946f224df5aae64c72538672eb74637b3c9e\",\"created\":\"2016-03-18T18:22:48.262403239Z\",\"container_config\":{\"Cmd\":[\"/bin/sh -c #(nop) ADD file:47ca6e777c36a4cfffe3f918b64a445c8f32300deeb9dfa5cc47261bd7b75d21 in /\"]}}"
      }
   ],
   "signatures": [
      {
         "header": {
            "jwk": {
               "crv": "P-256",
               "kid": "FIFX:SJRD:AQHW:MCFX:M6WC:LXI2:3VO2:4LFW:UHDZ:QUN7:OLX4:6WGD",
               "kty": "EC",
               "x": "Xm8wJTzw3nb--rGoD3dxjKffikj7Snb9dHW-qGbqSAM",
               "y": "GnATS--7lVcA_-jQGuDKTtjhmnGgvBrx8rLdlPOJV3U"
            },
            "alg": "ES256"
         },
         "signature": "f8NVzOF6ujm_0COedniGCGL_q3KsTfKFM9T8ZZDf2MSIMJ3TYoR_s795NqdEy8yWaoLuT2LoI0BCEsuOTZUhCw",
         "protected": "eyJmb3JtYXRMZW5ndGgiOjE5MTQsImZvcm1hdFRhaWwiOiJDbjAiLCJ0aW1lIjoiMjAxNi0wNi0xMVQwMToxMzoyMVoifQ"
      }
   ]
bash$ curl -I http://localhost:5000/v2/busybox/manifests/latest
HTTP/1.1 200 OK
Content-Length: 2561
Content-Type: application/vnd.docker.distribution.manifest.v1+prettyjws
Docker-Content-Digest: sha256:e45f25b1760f616e65f106b424f4ef29185fbd80822255d79dabc73b8eb715ad
Docker-Distribution-Api-Version: registry/2.0
Etag: "sha256:e45f25b1760f616e65f106b424f4ef29185fbd80822255d79dabc73b8eb715ad"
X-Content-Type-Options: nosniff
Date: Sat, 11 Jun 2016 01:21:26 GMT

No where in any of those API calls could I find the desired 47bcc53... image id that I see locally.

bash$ docker inspect busybox:latest
[
    {
        "Id": "sha256:47bcc53f74dc94b1920f0b34f6036096526296767650f223433fe65c35f149eb",
        "RepoTags": [
            "busybox:latest",
            "localhost:5000/busybox:latest"
        ],
        "RepoDigests": [],
        "Parent": "",
        "Comment": "",
        "Created": "2016-03-18T18:22:48.810791943Z",
        "Container": "5f8098ec29947b5bea80483cd3275008911ce87438fed628e34ec0c522665510",
        "ContainerConfig": {
            "Hostname": "156e10b83429",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": null,
            "Cmd": [
                "/bin/sh",
                "-c",
                "#(nop) CMD [\"sh\"]"
            ],
            "Image": "56ed16bd6310cca65920c653a9bb22de6b235990dcaa1742ff839867aed730e5",
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {}
        },
        "DockerVersion": "1.9.1",
        "Author": "",
        "Config": {
            "Hostname": "156e10b83429",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": null,
            "Cmd": [
                "sh"
            ],
            "Image": "56ed16bd6310cca65920c653a9bb22de6b235990dcaa1742ff839867aed730e5",
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {}
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 1112820,
        "VirtualSize": 1112820,
        "GraphDriver": {
            "Name": "aufs",
            "Data": null
        },
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:1834950e52ce4d5a88a1bbd131c537f4d0e56d10ff0dd69e66be3b7dfa9df7e6",
                "sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef"
            ]
        }
    }
]

From this image spec the image id is a reproducible hash, and I do see the same value for the image id on different systems.

ImageID Each image's ID is given by the SHA256 hash of its configuration JSON. It is represented as a hexadecimal encoding of 256 bits, e.g., sha256:a9561eb1b190625c9adb5a9513e72c4dedafc1cb2d4c5236c9a6957ec7dfd5a9. Since the configuration JSON that gets hashed references hashes of each layer in the image, this formulation of the ImageID makes images content-addresable.

So if you can reproduce the configuration JSON from the API calls, then you may be able to generate the image id yourself.

来源：https://stackoverflow.com/questions/37758258/is-that-possible-to-get-image-id-from-docker-registry-v2