ARO needs to copy RHCOS image blobs to their own Azure Marketplace offering since, as a first party Azure service, they must not request anything from outside of Azure and must consume RHCOS VM images from a trusted source (marketplace).
To meet the requirements ARO team currently does the following as part of the release process:

 1. Mirror container images from quay.io to Azure Container Registry to avoid leaving Azure boundaries.
 2. Copy VM image from the blob in someone else's Azure subscription
 into the blob on the subscription ARO team manages and then we publish a VM image on Azure Marketplace (publisher: azureopenshift, offer: aro4. See az vm image list --publisher azureopenshift --all). We do not bill for these images.

The usage of Marketplace images in the installer was already implemented as part of CORS-1823. This single line [1] needs to be refactored to enable ARO from the installer code perspective: on ARO we don't need to set type to AzureImageTypeMarketplaceWithPlan.

However, in OCPPLAN-7556 and related CORS-1823 it was mentioned that using Marketplace images is out of scope for nodes other than compute. For ARO we need to be able to use marketplace images for all nodes.

[1] https://github.com/openshift/installer/blob/f912534f12491721e3874e2bf64f7fa8d44aa7f5/pkg/asset/machines/azure/machines.go#L107

4.13

Always

1. Set RHCOS image from Azure Marketplace in the installconfig
2. Deploy a cluster
3.

Only compute nodes use the Marketplace image.

All nodes created by the Installer use RHCOS image coming from Azure Marketplace.