Currently we don't have a mechanism to override the coreos baseISO used by the assisted-installer. There is an environment variable - OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE but that is not being passed into the assisted-service.

This came up when debugging https://issues.redhat.com/browse/OCPBUGS-8081. A fix was proposed and a new coreos was built with the fix. Although we could replace the baseISO used by the agent installer the actual base ISO used by the bootstrap was taken from the release image.

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