Docker – pushing an image with two tags to gcr.io results in two different images

dockergoogle-kubernetes-engine

I'm doing the following:

docker build -t gcr.io/projid/imgname:333 -t gcr.io/projid/imgname:latest .

docker login -u _json_key -p "$(cat /secrets/service-account.json)" https://gcr.io

docker push gcr.io/projid/imgname:333

docker push gcr.io/projid/imgname:latest

Output of 1st push command:

Pushing to google container registry ...
The push refers to a repository [gcr.io/projid/imgname]
24af4f7c7118: Preparing
17b0972980d8: Preparing
6d6a6425aacb: Preparing
809c8c0dd73c: Preparing
e8d45b8ab3ca: Preparing
e8fa134cb7b8: Preparing
7cbcbac42c44: Preparing
e8fa134cb7b8: Waiting
7cbcbac42c44: Waiting
809c8c0dd73c: Layer already exists
e8d45b8ab3ca: Layer already exists
7cbcbac42c44: Layer already exists
e8fa134cb7b8: Layer already exists
17b0972980d8: Pushed
24af4f7c7118: Pushed
6d6a6425aacb: Pushed
333: digest: sha256:dae8cf914ba49928e6f0a34f6740802403813e6d10aa1c1d448a62ce9bb69066 size: 1779

Output of 2nd push command:

Pushing to google container registry ...
The push refers to a repository [gcr.io/projid/imgname]
24af4f7c7118: Preparing
17b0972980d8: Preparing
6d6a6425aacb: Preparing
809c8c0dd73c: Preparing
e8d45b8ab3ca: Preparing
e8fa134cb7b8: Preparing
7cbcbac42c44: Preparing
e8fa134cb7b8: Waiting
7cbcbac42c44: Waiting
e8d45b8ab3ca: Layer already exists
809c8c0dd73c: Layer already exists
24af4f7c7118: Layer already exists
17b0972980d8: Layer already exists
6d6a6425aacb: Layer already exists
7cbcbac42c44: Layer already exists
e8fa134cb7b8: Layer already exists
latest: digest: sha256:4f57375919829982741d095f8917306fe0c1410e115d030179bae4b8e4299c30 size: 1742

Question: Why the same image with two tags results in two different images in google container registry?

Best Answer

You are certainly pushing two image tags. I suggest building with a single tag, then adding the second one and pushing the image tags one by one. If the second one adds a new digest is a GCR bug. I have ran into this bug and solved by deleting the repository so it gets re-created at the next push. In my configuration the Docker version was also a factor. Version 17.04.0-ce, build 4845c56 would trigger the extra digest while version 17.03.1-ce, build c6d412e would work fine.

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