containers-registries.d man page

Miloslav Trmač August 2016

containers-registries.d — Directory for various registries configurations

Description

The registries configuration directory contains configuration for various registries (servers storing remote container images), and for content stored in them, so that the configuration does not have to be provided in command-line options over and over for every command, and so that it can be shared by all users of containers/image.

By default (unless overridden at compile-time), the registries configuration directory is /etc/containers/registries.d; applications may allow using a different directory instead.

Directory Structure

The directory may contain any number of files with the extension .yaml, each using the YAML format.  Other than the mandatory extension, names of the files don’t matter.

The contents of these files are merged together; to have a well-defined and easy to understand behavior, there can be only one configuration section describing a single namespace within a registry (in particular there can be at most one one default-docker section across all files, and there can be at most one instance of any key under the the docker section; these sections are documented later).

Thus, it is forbidden to have two conflicting configurations for a single registry or scope, and it is also forbidden to split a configuration for a single registry or scope across more than one file (even if they are not semantically in conflict).

Registries, Scopes and Search Order

Each YAML file must contain a “YAML mapping” (key-value pairs).  Two top-level keys are defined:

This key is optional.

This key is optional.

Scopes matching individual images are named Docker references in the fully expanded form, either
  using a tag or digest. For example, docker.io/library/busybox:latest (not busybox:latest).

More general scopes are prefixes of individual-image scopes, and specify a repository (by omitting the tag or digest),
  a repository namespace, or a registry host (and a port if it differs from the default).

Note that if a registry is accessed using a hostname+port configuration, the port-less hostname
  is not used as parent scope.

When searching for a configuration to apply for an individual container image, only the configuration for the most-precisely matching scope is used; configuration using more general scopes is ignored.  For example, if any configuration exists for docker.io/library/busybox, the configuration for docker.io is ignored (even if some element of the configuration is defined for docker.io and not for docker.io/library/busybox).

Individual Configuration Sections

A single configuration section is selected for a container image using the process described above.  The configuration section is a YAML mapping, with the following keys:

This key is optional; if it is missing, sigstore below is used.

This key is optional; if it is missing, no signature storage is defined (no signatures
  are download along with images, adding new signatures is possible only if sigstore-staging is defined).

Examples

Using Containers from Various Origins

The following demonstrates how to to consume and run images from various registries and namespaces:

docker:
    registry.database-supplier.com:
        sigstore: https://sigstore.database-supplier.com
    distribution.great-middleware.org:
        sigstore: https://security-team.great-middleware.org/sigstore
    docker.io/web-framework:
        sigstore: https://sigstore.web-framework.io:8080

Developing and Signing Containers, Staging Signatures

For developers in example.com:

  • Consume most container images using the public servers also used by clients.
  • Use a separate sigure storage for an container images in a namespace corresponding to the developers' department, with a staging storage used before publishing signatures.
  • Craft an individual exception for a single branch a specific developer is working on locally.
docker:
    registry.example.com:
        sigstore: https://registry-sigstore.example.com
    registry.example.com/mydepartment:
        sigstore: https://sigstore.mydepartment.example.com
        sigstore-staging: file:///mnt/mydepartment/sigstore-staging
    registry.example.com/mydepartment/myproject:mybranch:
        sigstore: http://localhost:4242/sigstore
        sigstore-staging: file:///home/useraccount/webroot/sigstore

A Global Default

If a company publishes its products using a different domain, and different registry hostname for each of them, it is still possible to use a single signature storage server without listing each domain individually. This is expected to rarely happen, usually only for staging new signatures.

default-docker:
    sigstore-staging: file:///mnt/company/common-sigstore-staging

Authors

Miloslav Trmač mitr@redhat.com ⟨mailto:mitr@redhat.com⟩

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