Support ImageContentSourcePolicy for image registry pull-through

User Story

As a user of a disconnected OpenShift cluster
I want the image registry to pull images from mirrors
So that I can use the internal registry as an additional pull-through cache in disconnected clusters

Acceptance Criteria

• In a disconnected cluster, pods which use ImageStreams with ReferencePolicy: Local pull images from the internal registry instead of referenced upstream repository.

Launch Checklist

Dependencies identified
Blockers noted and expected delivery timelines set
Design is implementable
Acceptance criteria agreed upon
Story estimated

Notes

The samples operator images all use pull-through (--refeference-policy=local for performance. Also has added benefit of not requiring users to add pull secrets to registry.redhat.io. Adding this facilitates the usage of sample imagestreams in disconnected environments, as well as allowing customers who create their own imagestreams in disconnected environments.

Azure Red Hat OpenShift (ARO) mirrors everything in the image payload, rather than pulling from quay.io. The Jenkins imagestream breaks because import doesn't use the mirror.

The main ask is to copy logic in openshift-apiserver to the image registry. If possible, the logic should be shared in a common repo (library-go? runtime-utils?). Blob lookup logic is likely impacted (need to check registries as well as mirrors).

Alternatives:

• Switch to using source policies in openshift/library. This would require numerous upstream PRs to be merged into openshift/library, and could lead to us breaking customers who assume they don't need pull secrets to registry.redhat.io
• Update the samples operator to let us be more granular in adjusting the image references.

Add pertinent notes here:

• Enhancement proposal link
• Previous product docs
• Best practices
• Known issues

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Guiding Questions

User Story

• Is this intended for an administrator, application developer, or other type of OpenShift user?
• What experience level is this intended for? New, experienced, etc.?
• Why is this story important? What problems does this solve? What benefit(s) will the customer experience?
• Is this part of a larger epic or initiative? If so, ensure that the story is linked to the appropriate epic and/or initiative.

Acceptance Criteria

• How should a customer use and/or configure the feature?
• Are there any prerequisites for using/enabling the feature?

Notes

• Is this a new feature, or an enhancement of an existing feature? If the latter, list the feature and docs reference.
• Are there any new terms, abbreviations, or commands introduced with this story? Ex: a new command line argument, a new custom resource.
• Are there any recommended best practices when using this feature?
• On feature completion, are there any known issues that customers should be aware of?