Tags

What is tag

Tags are notation for a image, a same image may have multiple tags. But the tag for named image can only represent one image. As long as at least one tag exists for the image, the image itself(distinct by id) won't be removed. So adding a new tag for image actually made a fork from it.

Add tag for existing image

docker images


REPOSITORY   TAG       IMAGE ID       CREATED          SIZE
vue-app      latest    d70d1656b8d2   32 minutes ago   420MB
ubuntu       latest    e4c58958181a   5 weeks ago      77.8MB

docker image tag vue-app vue-app:1

The new tag ref to the same container with the same id.

docker images


REPOSITORY   TAG       IMAGE ID       CREATED          SIZE
vue-app      1         d70d1656b8d2   33 minutes ago   420MB
vue-app      latest    d70d1656b8d2   33 minutes ago   420MB
ubuntu       latest    e4c58958181a   5 weeks ago      77.8MB

Assign tag when build

Assign tag after colon, if not specified, latest is the default.

docker build --tag vue-app:2 .

Remove tag

docker images

REPOSITORY   TAG       IMAGE ID       CREATED         SIZE
vue-app      latest    9a138abb00e2   4 minutes ago   420MB
vue-app      1         d70d1656b8d2   3 hours ago     420MB
ubuntu       latest    e4c58958181a   5 weeks ago     77.8MB

We perform docker image remove <container:tag> to remove its fork.

docker image remove vue-app:1

Untagged: vue-app:1
Deleted: sha256:d70d1656b8d292bfaecdee9f943e07580cdbabd8dd9ce7753c94645af2b0f6d9

Since it's the last existing image for this image, so when we remove its tag, meaning that this image shall be deleted forever.