Chapter 4. Image-naming conventions

4.1. Red Hat’s Naming Policy

Red Hat has provided a consistent naming policy for Docker-formatted images in order to provide predictability for users.

Docker URLs in the V1 version of the protocol and registry format work similar to GitHub repository names. Their structure is:

REGISTRY[:PORT]/USER/REPO[:TAG]

The implicit default registry is docker.io. This means that relative URLs, such as "redhat/rhel" resolve to docker.io/redhat/rhel.

The special name "library/*" maps to direct, non-prefixed images. For instance: "docker.io/rhel".

4.2. Redirection of Requests

Requests for Red Hat content are redirected from docker.io to registry.access.redhat.com. The following mappings describe this redirection:

  • docker.io/rhel → registry.access.redhat.com/rhel (alias for rhel7)
  • docker.io/rhel7 → registry.access.redhat.com/rhel7
  • docker.io/rhel6 → registry.access.redhat.com/rhel6
  • docker.io/redhat/* → registry.access.redhat.com/redhat/*

The version of Docker that ships with Red Hat Enterprise Linux 7.2 contacts the internal Red Hat registry by default. This allows Red Hat to segment the namespace by registry.

The registry content is a mapping of tagged names and does not involve any copying of content. This mapping is achieved by means of multiple symbolic links. Red Hat keeps these links up-to-date to ensure the integrity of your data.

The REPO is a repository containing a number of explicitly tagged and a number of hidden layers. An 'IMAGE' is a specific layer-complete branch within a repository. Often the terms 'image' and 'repository' are used synonymously, even thought they are not the same. For instance, different images can be tagged into a single repository.