10.1 Registry Concepts
A focused guide to Registry Concepts, connecting core concepts with practical Docker and container operations.
Registry concepts cover the foundational vocabulary and structure underlying how container registries organize and identify images — repositories, tags, namespaces, and digests — providing the shared terminology needed to understand registry interactions clearly.
Repositories as Named Collections of an Image's Versions
A repository groups together every version of a particular image under a shared name, with individual tags distinguishing specific versions within it.
docker pull postgres:16
docker pull postgres:15
docker pull postgres:14
All three of these pulls reference the same postgres repository, differing only in which tagged version is requested.
Namespaces Organizing Images by Publisher or Organization
A namespace, appearing as a prefix in an image's full name, identifies which organization or individual published a particular repository.
docker pull myteam/myapi:2.3.0
Here, myteam is the namespace, distinguishing this repository from a similarly named one published by a different organization.
Tags as Human-Readable Version Identifiers
A tag provides a memorable, human-readable label for a specific version within a repository, though as a mutable label, a given tag's underlying content can in principle change over time.
docker pull node:20-alpine
Digests as Immutable Content Identifiers
A digest, a cryptographic hash of an image's actual content, provides an immutable identifier guaranteed to always refer to exactly the same content, unlike a tag.
docker pull node@sha256:a1b2c3d4e5f6...
Why Registry Concepts Matter
A clear grasp of this foundational vocabulary — repositories, namespaces, tags, digests — is essential for accurately understanding and discussing how images are organized, versioned, and referenced within any registry, public or private.