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We want to check if an image exists in the public registry (Docker Hub) automatically before we start a deployment. With the v1 API, we would just query https://index.docker.io/v1/repositories/gliderlabs/alpine/tags/3.2 for example.

But now the official API for the registry is v2, what is the official way of checking the existence of an image in the public registry?

v1

$ curl -i https://index.docker.io/v1/repositories/gliderlabs/alpine/tags/latest
HTTP/1.1 200 OK
Server: nginx/1.6.2
Date: Tue, 11 Aug 2015 10:02:09 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Strict-Transport-Security: max-age=31536000

[{"pk": 20307475, "id": "5bd56d81"}, {"pk": 20355979, "id": "511136ea"}]

v2:

$ curl -i https://index.docker.io/v2/repositories/gliderlabs/alpine/tags/latest
HTTP/1.1 301 MOVED PERMANENTLY
Server: nginx/1.6.2
Date: Tue, 11 Aug 2015 10:04:20 GMT
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
X-Frame-Options: SAMEORIGIN
Location: https://index.docker.io/v2/repositories/gliderlabs/alpine/tags/latest/
Strict-Transport-Security: max-age=31536000

$ curl -i https://index.docker.io/v2/repositories/gliderlabs/alpine/tags/latest/
HTTP/1.1 301 MOVED PERMANENTLY
Server: nginx/1.6.2
Date: Tue, 11 Aug 2015 10:04:26 GMT
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
X-Frame-Options: SAMEORIGIN
Location: https://registry.hub.docker.com/v2/repositories/gliderlabs/alpine/tags/latest/
Strict-Transport-Security: max-age=31536000

$ curl -i https://registry.hub.docker.com/v2/repositories/gliderlabs/alpine/tags/latest/
HTTP/1.1 200 OK
Server: nginx/1.6.2
Date: Tue, 11 Aug 2015 10:04:34 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Allow: GET, DELETE, HEAD, OPTIONS
Strict-Transport-Security: max-age=31536000

{"name": "latest", "full_size": 5250074, "id": 130839, "repository": 127805, "creator": 152141, "last_updater": 152141, "image_id": null, "v2": false}

Am I supposed to stick to the v1 url even though it is now kind of deprecated or use v2 URLs but there is no documentation about it? If I use v2, shall I use directly https://registry.hub.docker.com/v2/ or still use https://index.docker.io/v1/ and follow the redirects?

WispyCloud
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    Possible duplicate: http://stackoverflow.com/questions/30113726/docker-registry-2-0-api-v2 – Kasisnu Aug 11 '15 at 04:58
  • This is not a duplicate, the linked question is about the private registry that you can run yourself, this question is about the public registry i.e. dockerhub. – WispyCloud Aug 11 '15 at 07:58
  • The v2 api is spec'd out at https://github.com/docker/distribution/blob/master/docs/spec/api.md. That is a part of the distribution project which lets you run a private registry. – Kasisnu Aug 11 '15 at 09:32
  • @Kasisnu Yes I know that but there is no official word for the public registry. Going to add a bit of details to the question. – WispyCloud Aug 11 '15 at 10:01
  • @jtblin Did you ever rind a solution for this? – jmreicha May 04 '16 at 19:40

1 Answers1

3

Upstream's download-frozen-image-v2.sh script should be of some use as at least a decent API example here (https://github.com/docker/docker/blob/6bf8844f1179108b9fabd271a655bf9eaaf1ee8c/contrib/download-frozen-image-v2.sh#L47-L54).

The main key is that you'll need to be hitting registry-1.docker.io instead of index.docker.io, and that you need a "token" from auth.docker.io (https://auth.docker.io/token?service=registry.docker.io&scope=repository:gliderlabs/alpine:pull), even if you're just requesting read-only access to a public repository. Once you've got that token, you can hit https://registry-1.docker.io/v2/gliderlabs/alpine/manifests/latest with an Authorization header which will either return the JSON manifest of the image or error out with a 404.

token="$(curl -sSL "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$image:pull" | jq --raw-output .token)"

curl -fsSL -H "Authorization: Bearer $token" "https://registry-1.docker.io/v2/$image/manifests/$digest"
tianon
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