Tagging an image

Each image has a so-called tag. A tag is often used to version images, but it has a broader reach than just being a version number. If we do not explicitly specify a tag when working with images, then Docker automatically assumes we're referring to the latest tag. This is relevant when pulling an image from Docker Hub, for example:

$ docker image pull alpine

The preceding command will pull the alpine:latest image from the Hub. If we want to explicitly specify a tag, we do so like this:

$ docker image pull alpine:3.5

This will now pull the alpine image that has been tagged with 3.5.