10.1.2 Registry Authentication
A focused guide to Registry Authentication, connecting core concepts with practical Docker and container operations.
Registry authentication is the process of proving identity and authorization to a registry before performing an action — typically pulling a private image or pushing any image at all — preventing unauthorized access to private content and unauthorized publishing under a given namespace.
Authenticating With a Registry
The login command establishes an authenticated session with a specified registry, persisting credentials for subsequent commands.
docker login registry.example.com
Username: myuser
Password: ********
Login Succeeded
Subsequent push and pull commands against this registry now use these established credentials automatically.
Why Public Images Often Don't Require Authentication
A public repository on Docker Hub or another registry can typically be pulled without any authentication at all, since public content is, by definition, intended to be freely accessible.
docker pull postgres:16
This succeeds without any prior docker login, since the official postgres image is publicly accessible.
Why Pushing Almost Always Requires Authentication
Regardless of whether the target repository will ultimately be public or private, pushing to it requires authentication, ensuring only authorized accounts can publish images under a given namespace.
docker push registry.example.com/myteam/myapi:2.3.0
unauthorized: authentication required
Without prior authentication, this push fails, since the registry has no basis for trusting this client to publish under this namespace.
Logging Out to End an Authenticated Session
Explicitly logging out removes stored credentials for a given registry, useful on a shared machine or when switching between different accounts.
docker logout registry.example.com
Why Registry Authentication Matters
Authentication is the fundamental mechanism that keeps a registry's access appropriately controlled — open enough for public content to be freely consumed, while still requiring proven authorization for any action, like pushing, that could affect what a registry actually serves to others.