Image Addressing Convention

In this lesson, you’ll learn how Docker interprets image names when you pull or reference them. Understanding these conventions helps you avoid naming conflicts and ensures you’re pulling or pushing images to the correct registry.

Pulling an Image

For example, running:

docker image pull httpd

might look simple—but what does httpd actually represent, and where does Docker retrieve it from?

Docker Image Naming Components

A complete Docker image reference can include up to three parts:

Implicit Namespace

When you specify only httpd, Docker assumes you want the official image from Docker Hub’s library namespace.
Effectively, Docker interprets:

image: library/httpd

Here, library is the namespace for curated, official images on Docker Hub, and httpd is the repository name.

Default Registry

By default, Docker pulls from Docker Hub (docker.io). Omitting the registry is shorthand for:

image: docker.io/library/httpd

The registry is where images are stored. When you build and push an image, it goes to this registry; when you pull, it comes from here.

docker image inspect httpd --format '{{.RepoDigests}}'

Referencing Other Registries

If your image lives in a different registry—such as Google Container Registry or a private registry—you must prepend the registry hostname:

# Google Container Registry (GCR)
image: gcr.io/your-project/httpd

# Private registry
image: registry.example.com/your-namespace/httpd

Before interacting with private registries, authenticate using:

docker login <registry-hostname>

Links and References

• Docker Image Overview
• Docker Hub Documentation
• Google Container Registry