RHEL image mode (rhel bootc) provides an easy way to create derived image by using the container build workflow.

A pod VM image build will look something like this

FROM registry.redhat.io/rhel9/rhel-bootc:9.4

# Download the pod VM payload
# RUN wget ....

# Extract the payload image to appropriate location
# RUN tar xvf ...

# Perform any other customisations

Build the image using podman build or buildah command. 

It supports creating images in different formats using bootc-image-builder -  qcow2, raw, AMI etc.

Using RHEL image mode (rhel-bootc) will align the pod VM build to the simpler mechanism leveraging RHEL image-mode. Also this will make it easier to pre-build the pod VM images which is an important requirement for CoCo.

There are few additional CoCo requirements that needs to be explored with RHEL image mode

1. Creating dm-verity (or fs-verity) based image
2. Capturing measurements and storing it as part of the container image

More details on RHEL image model is available here 

https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/using_image_mode_for_rhel_to_build_deploy_and_manage_operating_systems/introducing-image-mode-for-rhel_using-image-mode-for-rhel-to-build-deploy-and-manage-operating-systems

https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/using_image_mode_for_rhel_to_build_deploy_and_manage_operating_systems/creating-bootc-compatible-base-disk-images-with-bootc-image-builder_using-image-mode-for-rhel-to-build-deploy-and-manage-operating-systems#creating-ami-images-by-using-bootc-image-builder-and-uploading-it-to-aws_creating-bootc-compatible-base-disk-images-with-bootc-image-builder