CODEWITHSUNDEEP
dockerdocker-registry
nVitius
nVitius

Reputation: 2224

Comparing Docker Tags

Given that I build and tag an image like so:

docker build -t foo:bar .
docker tag foo:bar foo:baz

How can I. later, confirm whether or not the two tags refer to the same thing? I would like to be able to do this through the Registry API (v2), since I might not have both images locally.

Upvotes: 1

Views: 1123

Answers (1)

Nicolas
Nicolas

Reputation: 2231

One (tedious?) way of doing that includes comparing the fsLayers registered in the manifest file attached to each tag:

Download http://your-registry/v2/repo/image/manifests/tag1 and http://your-registry/v2/repo/image/manifests/tag2:

{
    "name": "repo/image",
    "tag": "tag1",
    "architecture": "amd64",
    "fsLayers": [{
        "blobSum": "sha256:d7958e841d1f103cc24e45cb6108eaf09ecf0b424f071ac6b6ab39241cec293d"
    }, {
        "blobSum": "sha256:d7958e841d1f103cc24e45cb6108eaf09ecf0b424f071ac6b6ab39241cec293d"
    }, {
        "blobSum": "sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4"
    }],
    "history": [
        (...)
    ],
    "schemaVersion": 1,
    "signatures": [{
        "header": { (...) },
        "signature": "PwuBjXLvQE_DtF29YtyJF2N-zHkVGRh93It4zxL1Igtoi093ykMvXBL_0J6E6-eQVeYrXm3IdDAll-922zeYzQ",
        "protected": "eyJmb3JtYXRMZW5ndGgiOjIwOTk0LCJmb3JtYXRUYWlsIjoiQ24wIiwidGltZSI6IjIwMTUtMTItMDdUMTM6NDE6MjJaIn0"
    }]
}

Then compare the fsLayers array. If it is equal between the two manifests, then building a container based on any of these tags will give the same results (i.e. they point to the same thing).

If you have the images locally, comparing the imageId (via docker inspect for each tag) is enough and easier. But I don't think that this id can be obtained from the registry.

Upvotes: 2

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