Tagging images

Learn to tag images with the -t flag.

Tagging images

A full image name has the form [registry/][user/]repository:tag. The tag usually shows the version. One build can get several tags:

docker build -t api:1.4.2 -t api:1.4 -t api:latest .
docker build -t ghcr.io/ali/api:1.4.2 .

Semantic versioning (major.minor.patch) is common: 1.4.2 is fixed, while 1.4 and latest are moving tags pointing at the latest patch.

A tag is a pointer

A tag is a name pointing at an image ID (content digest); the same image can have several tags. docker tag adds a new name, the image isn't copied:

$ docker tag api:1.4.2 ali/api:1.4.2
$ docker images
REPOSITORY   TAG     IMAGE ID       SIZE
api          1.4.2   4f1e2d3c4b5a   162MB
ali/api      1.4.2   4f1e2d3c4b5a   162MB    # same ID

Exercise Multiple tags

Write the command that produces the tags api:2.0.1, api:2.0 and api:latest from the current folder with a single build.

Test yourself

Why is a fixed version tag used in production instead of latest?
- latest can't be pulled
- latest is only for Windows
- latest may point at different images over time; rollback and reproduction get hard
- latest is slower
Show answer

latest may point at different images over time; rollback and reproduction get hard — Knowing which version runs is the first step of debugging.

Give an existing image a new name.

docker ____ api:1.4.2 ali/api:1.4.2

Show answer

docker tag api:1.4.2 ali/api:1.4.2

Match.

1.4.2

Fixed version
1.4

Moving minor version
ghcr.io/

Registry address
IMAGE ID

Content ID

Next lesson: Build context

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies