Lowercase images names in Docker

Why does Docker only allow lowercase letters for image names?

Why not uppercase letters?

During the commit of a container:

docker commit [OPTIONS] CONTAINER [REPOSITORY[:TAG]]

Are docker image tags case sensitive?

A tag name must be valid ASCII and may contain lowercase and uppercase letters, digits, underscores, periods and dashes. A tag name may not start with a period or a dash and may contain a maximum of 128 characters.

How do I name an image in docker?

You can rename your docker image by docker tag command. Use the below given command to do that. To rename docker container, use the rename sub-command as shown, in the following example, we renaming the container discourse_app to a new name disc_app.

Why should docker images be small?

Smaller Docker images take up less disk space. A Docker image is composed of reusable layers, i.e. different images might share some layers. Because of such architecture, image size and disk consumption are not necessarily directly correlated.

This was a design choice; technically, there should probably be no real issues with allowing mixed-case names, but we decided to stick with lowercase for now (which keeps the road open to allow uppercase characters in future, without breaking backward compatibility).