I am trying to tag a Docker image sitting in Google Container Registry but am not having any luck. If the image were sitting on my local machine, i could do something like:

docker tag my-image:existing-tag my-image:new-tag

This would result in a second tag for my image. However, in Google Container Registry, I cannot simply use the gcloud wrapper to do so. For example:

gcloud docker -- tag gcr.io/my-project/my-image:existing-tag gcr.io/my-project/my-image:new-tag

This command will not work because even though I am running with gcloud, I get the following response:

Error response from daemon: no such id gcr.io/my-project/my-image:existing-tag

Is what I am attempting possible, and how would one accomplish it?