Sharing or shipping images
To be able to ship our custom image to other environments, we need to give it a globally unique name. This action is often called tagging an image. We then need to publish the image to a central location from which other interested or entitled parties can pull it. These central locations are called image registries.
In the following sections, we will describe how this works in more detail.
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, as shown in the following example:
$ docker image pull alpine
The preceding command will pull the alpine:latest image from Docker Hub. If we want to explicitly specify a tag, we can do so like this:
$ docker image...
