2.9.3. Using signature transports

A signature transport is a way to store and retrieve the binary signature blob. There are two types of signature transports.

The OpenShift Container Platform API manages signatures that use the atomic transport type. You must store the images that use this signature type in your OpenShift Container Registry. Because the docker/distribution extensions API auto-discovers the image signature endpoint, no additional configuration is required.

Signatures that use the docker transport type are served by local file or web server. These signatures are more flexible; you can serve images from any container image registry and use an independent server to deliver binary signatures.

However, the docker transport type requires additional configuration. You must configure the nodes with the URI of the signature server by placing arbitrarily-named YAML files into a directory on the host system, /etc/containers/registries.d by default. The YAML configuration files contain a registry URI and a signature server URI, or sigstore:

docker:
    access.redhat.com:
        sigstore: https://access.redhat.com/webassets/docker/content/sigstore

In this example, the Red Hat Registry, access.redhat.com, is the signature server that provides signatures for the docker transport type. Its URI is defined in the sigstore parameter. You might name this file /etc/containers/registries.d/redhat.com.yaml and use the Machine Config Operator to automatically place the file on each node in your cluster. No service restart is required since policy and registries.d files are dynamically loaded by the container runtime.